Chemical element

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The chemical elements ordered in the periodic table Periodic table (32-col, enwiki), black and white.png
The chemical elements ordered in the periodic table

A chemical element is a chemical substance that cannot be broken down into other substances by chemical reactions. The basic particle that constitutes a chemical element is the atom. Chemical elements are identified by the number of protons in the nuclei of their atoms, [1] known as the element's atomic number. [2] For example, oxygen has an atomic number of 8, meaning that each oxygen atom has 8 protons in its nucleus. Two or more atoms of the same element can combine to form molecules, in contrast to chemical compounds or mixtures, which contain atoms of different elements. Atoms can be transformed into different elements in nuclear reactions, which change an atom's atomic number.


Almost all of the baryonic matter of the universe is composed of chemical elements (among rare exceptions are neutron stars). When different elements undergo chemical reactions, atoms are rearranged into new compounds held together by chemical bonds. Only a few elements, such as silver and gold, are found uncombined as relatively pure native element minerals. Nearly all other naturally occurring elements occur in the Earth as compounds or mixtures. Air is primarily a mixture of molecular nitrogen and oxygen, though it does contain compounds including carbon dioxide and water, as well as atomic argon, a noble gas which is chemically inert and therefore does not undergo chemical reactions.

The history of the discovery and use of the elements began with primitive human societies that discovered native minerals like carbon, sulfur, copper and gold (though the concept of a chemical element was not yet understood). Attempts to classify materials such as these resulted in the concepts of classical elements, alchemy, and various similar theories throughout human history. Much of the modern understanding of elements developed from the work of Dmitri Mendeleev, a Russian chemist who published the first recognizable periodic table in 1869. This table organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The periodic table summarizes various properties of the elements, allowing chemists to derive relationships between them and to make predictions about compounds and potential new ones.

By November 2016, the International Union of Pure and Applied Chemistry had recognized a total of 118 elements. The first 94 occur naturally on Earth, and the remaining 24 are synthetic elements produced in nuclear reactions. Save for unstable radioactive elements (radionuclides) which decay quickly, nearly all of the elements are available industrially in varying amounts. The discovery and synthesis of further new elements is an ongoing area of scientific study.


The lightest chemical elements are hydrogen and helium, both created by Big Bang nucleosynthesis during the first 20 minutes of the universe [3] in a ratio of around 3:1 by mass (or 12:1 by number of atoms), [4] [5] along with tiny traces of the next two elements, lithium and beryllium. Almost all other elements found in nature were made by various natural methods of nucleosynthesis. [6] On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation. New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay, beta decay, spontaneous fission, cluster decay, and other rarer modes of decay.

Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium, element 43 and promethium, element 61, which have no stable isotopes). Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System. At over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element, and is almost always considered on par with the 80 stable elements. [7] [8] The very heaviest elements (those beyond plutonium, element 94) undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized.

There are now 118 known elements. In this context, "known" means observed well enough, even from just a few decay products, to have been differentiated from other elements. [9] [10] Most recently, the synthesis of element 118 (since named oganesson) was reported in October 2006, and the synthesis of element 117 (tennessine) was reported in April 2010. [11] [12] Of these 118 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium, atomic number 43; promethium, number 61; astatine, number 85; francium, number 87; neptunium, number 93; and plutonium, number 94. These 94 elements have been detected in the universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made. The first 94 elements have been detected directly on Earth as primordial nuclides present from the formation of the Solar System, or as naturally occurring fission or transmutation products of uranium and thorium.

The remaining 24 heavier elements, not found today either on Earth or in astronomical spectra, have been produced artificially: these are all radioactive, with very short half-lives; if any atoms of these elements were present at the formation of Earth, they are extremely likely, to the point of certainty, to have already decayed, and if present in novae have been in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element synthesized, in 1937, although trace amounts of technetium have since been found in nature (and also the element may have been discovered naturally in 1925). [13] This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally occurring rare elements. [14]

List of the elements are available by name, atomic number, density, melting point, boiling point and by symbol, as well as ionization energies of the elements. The nuclides of stable and radioactive elements are also available as a list of nuclides, sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in the form of the periodic table, which groups together elements with similar chemical properties (and usually also similar electronic structures).

Atomic number

The atomic number of an element is equal to the number of protons in each atom, and defines the element. [15] For example, all carbon atoms contain 6 protons in their atomic nucleus; so the atomic number of carbon is 6. [16] Carbon atoms may have different numbers of neutrons; atoms of the same element having different numbers of neutrons are known as isotopes of the element. [17]

The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the number of electrons of the atom in its non-ionized state. The electrons are placed into atomic orbitals that determine the atom's various chemical properties. The number of neutrons in a nucleus usually has very little effect on an element's chemical properties (except in the case of hydrogen and deuterium). Thus, all carbon isotopes have nearly identical chemical properties because they all have six protons and six electrons, even though carbon atoms may, for example, have 6 or 8 neutrons. That is why the atomic number, rather than mass number or atomic weight, is considered the identifying characteristic of a chemical element.

The symbol for atomic number is Z.


Isotopes are atoms of the same element (that is, with the same number of protons in their atomic nucleus), but having different numbers of neutrons. Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons in the nucleus, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, the three isotopes of carbon are known as carbon-12, carbon-13, and carbon-14, often abbreviated to 12C, 13C, and 14C. Carbon in everyday life and in chemistry is a mixture of 12C (about 98.9%), 13C (about 1.1%) and about 1 atom per trillion of 14C.

Most (66 of 94) naturally occurring elements have more than one stable isotope. Except for the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of a given element are chemically nearly indistinguishable.

All of the elements have some isotopes that are radioactive (radioisotopes), although not all of these radioisotopes occur naturally. The radioisotopes typically decay into other elements upon radiating an alpha or beta particle. If an element has isotopes that are not radioactive, these are termed "stable" isotopes. All of the known stable isotopes occur naturally (see primordial isotope). The many radioisotopes that are not found in nature have been characterized after being artificially made. Certain elements have no stable isotopes and are composed only of radioactive isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82.

Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50).

Isotopic mass and atomic mass

The mass number of an element, A, is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a superscript on the left hand side of the atomic symbol (e.g. 238U). The mass number is always a whole number and has units of "nucleons". For example, magnesium-24 (24 is the mass number) is an atom with 24 nucleons (12 protons and 12 neutrons).

Whereas the mass number simply counts the total number of neutrons and protons and is thus a natural (or whole) number, the atomic mass of a particular isotope (or "nuclide") of the element is the mass of a single atom of that isotope, and is typically expressed in daltons (symbol: Da), or universal atomic mass units (symbol: u). Its relative atomic mass is a dimensionless number equal to the atomic mass divided by the atomic mass constant, which equals 1 Da. In general, the mass number of a given nuclide differs in value slightly from its relative atomic mass, since the mass of each proton and neutron is not exactly 1 Da; since the electrons contribute a lesser share to the atomic mass as neutron number exceeds proton number; and because of the nuclear binding energy and the electron binding energy. For example, the atomic mass of chlorine-35 to five significant digits is 34.969 Da and that of chlorine-37 is 36.966 Da. However, the relative atomic mass of each isotope is quite close to its mass number (always within 1%). The only isotope whose atomic mass is exactly a natural number is 12C, which has a mass of 12 Da because the dalton is defined as 1/12 of the mass of a free neutral carbon-12 atom in the ground state.

The standard atomic weight (commonly called "atomic weight") of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit. This number may be a fraction that is not close to a whole number. For example, the relative atomic mass of chlorine is 35.453 u, which differs greatly from a whole number as it is an average of about 76% chlorine-35 and 24% chlorine-37. Whenever a relative atomic mass value differs by more than 1% from a whole number, it is due to this averaging effect, as significant amounts of more than one isotope are naturally present in a sample of that element.

Chemically pure and isotopically pure

Chemists and nuclear scientists have different definitions of a pure element. In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the same atomic number, or number of protons. Nuclear scientists, however, define a pure element as one that consists of only one stable isotope. [18]

For example, a copper wire is 99.99% chemically pure if 99.99% of its atoms are copper, with 29 protons each. However it is not isotopically pure since ordinary copper consists of two stable isotopes, 69% 63Cu and 31% 65Cu, with different numbers of neutrons. However, a pure gold ingot would be both chemically and isotopically pure, since ordinary gold consists only of one isotope, 197Au.


Atoms of chemically pure elements may bond to each other chemically in more than one way, allowing the pure element to exist in multiple chemical structures (spatial arrangements of atoms), known as allotropes, which differ in their properties. For example, carbon can be found as diamond, which has a tetrahedral structure around each carbon atom; graphite, which has layers of carbon atoms with a hexagonal structure stacked on top of each other; graphene, which is a single layer of graphite that is very strong; fullerenes, which have nearly spherical shapes; and carbon nanotubes, which are tubes with a hexagonal structure (even these may differ from each other in electrical properties). The ability of an element to exist in one of many structural forms is known as 'allotropy'.

The reference state of an element is defined by convention, usually as the thermodynamically most stable allotrope and physical state at a pressure of 1 bar and a given temperature (typically at 298.15K). However, for phosphorus, the reference state is white phosphorus even though it is not the most stable allotrope. In thermochemistry, an element is defined to have an enthalpy of formation of zero in its reference state. For example, the reference state for carbon is graphite, because the structure of graphite is more stable than that of the other allotropes.


Several kinds of descriptive categorizations can be applied broadly to the elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins.

General properties

Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between metals, which readily conduct electricity, nonmetals, which do not, and a small group, (the metalloids ), having intermediate properties and often behaving as semiconductors.

A more refined classification is often shown in colored presentations of the periodic table. This system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals. The version of this classification used in the periodic tables presented here includes: actinides, alkali metals, alkaline earth metals, halogens, lanthanides, transition metals, post-transition metals, metalloids, reactive nonmetals, and noble gases. In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense. Similarly, the reactive nonmetals and the noble gases are nonmetals viewed in the broader sense. In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals.

States of matter

Another commonly used basic distinction among the elements is their state of matter (phase), whether solid, liquid, or gas, at a selected standard temperature and pressure (STP). Most of the elements are solids at conventional temperatures and atmospheric pressure, while several are gases. Only bromine and mercury are liquids at 0 degrees Celsius (32 degrees Fahrenheit) and normal atmospheric pressure; caesium and gallium are solids at that temperature, but melt at 28.4 °C (83.2 °F) and 29.8 °C (85.6 °F), respectively.

Melting and boiling points

Melting and boiling points, typically expressed in degrees Celsius at a pressure of one atmosphere, are commonly used in characterizing the various elements. While known for most elements, either or both of these measurements is still undetermined for some of the radioactive elements available in only tiny quantities. Since helium remains a liquid even at absolute zero at atmospheric pressure, it has only a boiling point, and not a melting point, in conventional presentations.


The density at selected standard temperature and pressure (STP) is frequently used in characterizing the elements. Density is often expressed in grams per cubic centimetre (g/cm3). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements.

When an element has allotropes with different densities, one representative allotrope is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon (amorphous carbon, graphite, and diamond) have densities of 1.8–2.1, 2.267, and 3.515 g/cm3, respectively.

Crystal structures

The elements studied to date as solid samples have eight kinds of crystal structures: cubic, body-centered cubic, face-centered cubic, hexagonal, monoclinic, orthorhombic, rhombohedral, and tetragonal. For some of the synthetically produced transuranic elements, available samples have been too small to determine crystal structures.

Occurrence and origin on Earth

Chemical elements may also be categorized by their origin on Earth, with the first 94 considered naturally occurring, while those with atomic numbers beyond 94 have only been produced artificially as the synthetic products of human-made nuclear reactions.

Of the 94 naturally occurring elements, 83 are considered primordial and either stable or weakly radioactive. The remaining 11 naturally occurring elements possess half lives too short for them to have been present at the beginning of the Solar System, and are therefore considered transient elements. Of these 11 transient elements, 5 (polonium, radon, radium, actinium, and protactinium) are relatively common decay products of thorium and uranium. The remaining 6 transient elements (technetium, promethium, astatine, francium, neptunium, and plutonium) occur only rarely, as products of rare decay modes or nuclear reaction processes involving uranium or other heavy elements.

No radioactive decay has been observed for elements with atomic numbers 1 through 82, except 43 (technetium) and 61 (promethium). Observationally stable isotopes of some elements (such as tungsten and lead), however, are predicted to be slightly radioactive with very long half-lives: [19] for example, the half-lives predicted for the observationally stable lead isotopes range from 1035 to 10189 years. Elements with atomic numbers 43, 61, and 83 through 94 are unstable enough that their radioactive decay can readily be detected. Three of these elements, bismuth (element 83), thorium (element 90), and uranium (element 92) have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of the Solar System. For example, at over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 has the longest known alpha decay half-life of any naturally occurring element. [7] [8] The very heaviest 24 elements (those beyond plutonium, element 94) undergo radioactive decay with short half-lives and cannot be produced as daughters of longer-lived elements, and thus are not known to occur in nature at all.

Periodic table

Group 1 2   3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Hydrogen &
alkali metals
Alkaline earth metalsTrielsTetrelsPnicto­gensChal­co­gensHalo­gensNoble


Hydro­gen1H1.0080 He­lium2He4.0026
2 Lith­ium3Li6.94 Beryl­lium4Be9.0122 Boron5B10.81 Carbon6C12.011 Nitro­gen7N14.007 Oxy­gen8O15.999 Fluor­ine9F18.998 Neon10Ne20.180
3 So­dium11Na22.990 Magne­sium12Mg24.305 Alumin­ium13Al26.982 Sili­con14Si28.085 Phos­phorus15P30.974 Sulfur16S32.06 Chlor­ine17Cl35.45 Argon18Ar39.95
4 Potas­sium19K39.098 Cal­cium20Ca40.078 Scan­dium21Sc44.956 Tita­nium22Ti47.867 Vana­dium23V50.942 Chrom­ium24Cr51.996 Manga­nese25Mn54.938 Iron26Fe55.845 Cobalt27Co58.933 Nickel28Ni58.693 Copper29Cu63.546 Zinc30Zn65.38 Gallium31Ga69.723 Germa­nium32Ge72.630 Arsenic33As74.922 Sele­nium34Se78.971 Bromine35Br79.904 Kryp­ton36Kr83.798
5 Rubid­ium37Rb85.468 Stront­ium38Sr87.62 Yttrium39Y88.906 Zirco­nium40Zr91.224 Nio­bium41Nb92.906 Molyb­denum42Mo95.95 Tech­netium43Tc[97] Ruthe­nium44Ru101.07 Rho­dium45Rh102.91 Pallad­ium46Pd106.42 Silver47Ag107.87 Cad­mium48Cd112.41 Indium49In114.82 Tin50Sn118.71 Anti­mony51Sb121.76 Tellur­ium52Te127.60 Iodine53I126.90 Xenon54Xe131.29
6 Cae­sium55Cs132.91 Ba­rium56Ba137.33 Asterisks one.svg Lute­tium71Lu174.97 Haf­nium72Hf178.49 Tanta­lum73Ta180.95 Tung­sten74W183.84 Rhe­nium75Re186.21 Os­mium76Os190.23 Iridium77Ir192.22 Plat­inum78Pt195.08 Gold79Au196.97 Mer­cury80Hg200.59 Thallium81Tl204.38 Lead82Pb207.2 Bis­muth83Bi208.98 Polo­nium84Po[209] Asta­tine85At[210] Radon86Rn[222]
7 Fran­cium87Fr[223] Ra­dium88Ra[226] Asterisks 2 (vertical).svg Lawren­cium103Lr[266] Ruther­fordium104Rf[267] Dub­nium105Db[268] Sea­borgium106Sg[269] Bohr­ium107Bh[270] Has­sium108Hs[269] Meit­nerium109Mt[278] Darm­stadtium110Ds[281] Roent­genium111Rg[282] Coper­nicium112Cn[285] Nihon­ium113Nh[286] Flerov­ium114Fl[289] Moscov­ium115Mc[290] Liver­morium116Lv[293] Tenness­ine117Ts[294] Oga­nesson118Og[294]
Asterisks one.svg Lan­thanum57La138.91 Cerium58Ce140.12 Praseo­dymium59Pr140.91 Neo­dymium60Nd144.24 Prome­thium61Pm[145] Sama­rium62Sm150.36 Europ­ium63Eu151.96 Gadolin­ium64Gd157.25 Ter­bium65Tb158.93 Dyspro­sium66Dy162.50 Hol­mium67Ho164.93 Erbium68Er167.26 Thulium69Tm168.93 Ytter­bium70Yb173.05  
Asterisks 2 (vertical).svg Actin­ium89Ac[227] Thor­ium90Th232.04 Protac­tinium91Pa231.04 Ura­nium92U238.03 Neptu­nium93Np[237] Pluto­nium94Pu[244] Ameri­cium95Am[243] Curium96Cm[247] Berkel­ium97Bk[247] Califor­nium98Cf[251] Einstei­nium99Es[252] Fer­mium100Fm[257] Mende­levium101Md[258] Nobel­ium102No[259]

The properties of the chemical elements are often summarized using the periodic table, which powerfully and elegantly organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The current standard table contains 118 confirmed elements as of 2021.

Although earlier precursors to this presentation exist, its invention is generally credited to the Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring trends in the properties of the elements. The layout of the table has been refined and extended over time as new elements have been discovered and new theoretical models have been developed to explain chemical behavior.

Use of the periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior. The table has also found wide application in physics, geology, biology, materials science, engineering, agriculture, medicine, nutrition, environmental health, and astronomy. Its principles are especially important in chemical engineering.

Nomenclature and symbols

The various chemical elements are formally identified by their unique atomic numbers, by their accepted names, and by their symbols.

Atomic numbers

The known elements have atomic numbers from 1 through 118, conventionally presented as Arabic numerals. Since the elements can be uniquely sequenced by atomic number, conventionally from lowest to highest (as in a periodic table), sets of elements are sometimes specified by such notation as "through", "beyond", or "from ... through", as in "through iron", "beyond uranium", or "from lanthanum through lutetium". The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities), as in "lighter than carbon" or "heavier than lead", although technically the weight or mass of atoms of an element (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers.

Element names

The naming of various substances now known as elements precedes the atomic theory of matter, as names were given locally by various cultures to various minerals, metals, compounds, alloys, mixtures, and other materials, although at the time it was not known which chemicals were elements and which compounds. As they were identified as elements, the existing names for anciently known elements (e.g., gold, mercury, iron) were kept in most countries. National differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For a few illustrative examples: German speakers use "Wasserstoff" (water substance) for "hydrogen", "Sauerstoff" (acid substance) for "oxygen" and "Stickstoff" (smothering substance) for "nitrogen", while English and some romance languages use "sodium" for "natrium" and "potassium" for "kalium", and the French, Italians, Greeks, Portuguese and Poles prefer "azote/azot/azoto" (from roots meaning "no life") for "nitrogen".

For purposes of international communication and trade, the official names of the chemical elements both ancient and more recently recognized are decided by the International Union of Pure and Applied Chemistry (IUPAC), which has decided on a sort of international English language, drawing on traditional English names even when an element's chemical symbol is based on a Latin or other traditional word, for example adopting "gold" rather than "aurum" as the name for the 79th element (Au). IUPAC prefers the British spellings "aluminium" and "caesium" over the U.S. spellings "aluminum" and "cesium", and the U.S. "sulfur" over the British "sulphur". However, elements that are practical to sell in bulk in many countries often still have locally used national names, and countries whose national language does not use the Latin alphabet are likely to use the IUPAC element names.

According to IUPAC, chemical elements are not proper nouns in English; consequently, the full name of an element is not routinely capitalized in English, even if derived from a proper noun, as in californium and einsteinium. Isotope names of chemical elements are also uncapitalized if written out, e.g., carbon-12 or uranium-235. Chemical element symbols (such as Cf for californium and Es for einsteinium), are always capitalized (see below).

In the second half of the twentieth century, physics laboratories became able to produce nuclei of chemical elements with half-lives too short for an appreciable amount of them to exist at any time. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This practice can lead to the controversial question of which research group actually discovered an element, a question that delayed the naming of elements with atomic number of 104 and higher for a considerable amount of time. (See element naming controversy).

Precursors of such controversies involved the nationalistic namings of elements in the late 19th century. For example, lutetium was named in reference to Paris, France. The Germans were reluctant to relinquish naming rights to the French, often calling it cassiopeium. Similarly, the British discoverer of niobium originally named it columbium, in reference to the New World. It was used extensively as such by American publications before the international standardization (in 1950).

Chemical symbols

Specific chemical elements

Before chemistry became a science, alchemists had designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of atoms combining to form molecules. With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, to depict molecules.

The current system of chemical notation was invented by Jöns Jakob Berzelius in 1814. In this typographical system, chemical symbols are not mere abbreviations—though each consists of letters of the Latin alphabet. They are intended as universal symbols for people of all languages and alphabets.

Since Latin was the common language of science at Berzelius's time, his symbols were abbreviations based on the Latin names of elements (they may be Classical Latin names of elementary substances known since antiquity or Neo-Latin coinages for later elements). The symbols are not followed by a period (full stop) as with abbreviations. In most cases, Latin names of elements as used by Berzelius have the same roots as modern English names. For example, hydrogen has the chemical symbol "H" after the Neo-Latin hydrogenium, which has the same Ancient Greek roots as English hydrogen. However, in eleven cases Latin (as used by Berzelius) and English names of elements have different roots. Eight of them are the seven metals of antiquity and a metalloid also known since antiquity: "Fe" (Latin ferrum) for iron, "Hg" (Latin hydrargyrum) for mercury, "Sn" (Latin stannum) for tin, "Au" (Latin aurum) for gold, "Ag" (Latin argentum) for silver, "Pb" (Latin plumbum) for lead, "Cu" (Latin cuprum) for copper, and "Sb" (Latin stibium) for antimony. The three other mismatches between Neo-Latin (as used by Berzelius) and English names are "Na" (Neo-Latin natrium) for sodium, "K" (Neo-Latin kalium) for potassium, and "W" (Neo-Latin wolframium) for tungsten. These mismatches came from different suggestings of naming the elements in the Modern era. Initially Berzelius suggested "So" and "Po" for sodium and potassium, but he changed the symbols to "Na" and "K" later in the same year.

Elements discovered after 1814 were also assigned unique chemical symbols, based on the name of the element. The use of Latin as the universal language of science was fading, but chemical names of newly discovered elements came to be borrowed from language to language without or with little modifications. Symbols of elements discovered after 1814 match their names in English, French (ignoring the acute accent on é), and German (although German in many cases allows alternative spellings with k or z instead of c: e. g., the name of caesium may be spelled Caesium, Cäsium, or Zäsium in German, but its symbol is always "Cs"). Other languages sometimes modify element name spellings: Spanish iterbio (ytterbium), Italian afnio (hafnium), Swedish moskovium (moscovium); but those modifications do not affect chemical symbols: "Yb", "Hf", "Mc".

Chemical symbols are understood internationally when element names might require translation. There have sometimes been differences in the past. For example, Germans in the past have used "J" (for the alternate name Jod) for iodine, but now use "I" and Iod.

The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always lower case (small letters). Thus, the symbols for californium and einsteinium are Cf and Es.

General chemical symbols

There are also symbols in chemical equations for groups of chemical elements, for example in comparative formulas. These are often a single capital letter, and the letters are reserved and not used for names of specific elements. For example, an "X" indicates a variable group (usually a halogen) in a class of compounds, while "R" is a radical, meaning a compound structure such as a hydrocarbon chain. The letter "Q" is reserved for "heat" in a chemical reaction. "Y" is also often used as a general chemical symbol, although it is also the symbol of yttrium. "Z" is also frequently used as a general variable group. "E" is used in organic chemistry to denote an electron-withdrawing group or an electrophile; similarly "Nu" denotes a nucleophile. "L" is used to represent a general ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal.

At least two additional, two-letter generic chemical symbols are also in informal usage, "Ln" for any lanthanide element and "An" for any actinide element. "Rg" was formerly used for any rare gas element, but the group of rare gases has now been renamed noble gases and the symbol "Rg" has now been assigned to the element roentgenium.

Isotope symbols

Isotopes are distinguished by the atomic mass number (total protons and neutrons) for a particular isotope of an element, with this number combined with the pertinent element's symbol. IUPAC prefers that isotope symbols be written in superscript notation when practical, for example 12C and 235U. However, other notations, such as carbon-12 and uranium-235, or C-12 and U-235, are also used.

As a special case, the three naturally occurring isotopes of the element hydrogen are often specified as H for 1H (protium), D for 2H (deuterium), and T for 3H (tritium). This convention is easier to use in chemical equations, replacing the need to write out the mass number for each atom. For example, the formula for heavy water may be written D2O instead of 2H2O.

Origin of the elements

Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled "atoms" is composed of chemical elements. Universe content pie chart.jpg
Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled "atoms" is composed of chemical elements.

Only about 4% of the total mass of the universe is made of atoms or ions, and thus represented by chemical elements. This fraction is about 15% of the total matter, with the remainder of the matter (85%) being dark matter. The nature of dark matter is unknown, but it is not composed of atoms of chemical elements because it contains no protons, neutrons, or electrons. (The remaining non-matter part of the mass of the universe is composed of the even less well understood dark energy).

The 94 naturally occurring chemical elements were produced by at least four classes of astrophysical process. Most of the hydrogen, helium and a very small quantity of lithium were produced in the first few minutes of the Big Bang. This Big Bang nucleosynthesis happened only once; the other processes are ongoing. Nuclear fusion inside stars produces elements through stellar nucleosynthesis, including all elements from carbon to iron in atomic number. Elements higher in atomic number than iron, including heavy elements like uranium and plutonium, are produced by various forms of explosive nucleosynthesis in supernovae and neutron star mergers. The light elements lithium, beryllium and boron are produced mostly through cosmic ray spallation (fragmentation induced by cosmic rays) of carbon, nitrogen, and oxygen.

During the early phases of the Big Bang, nucleosynthesis of hydrogen nuclei resulted in the production of hydrogen-1 (protium, 1H) and helium-4 (4He), as well as a smaller amount of deuterium (2H) and very minuscule amounts (on the order of 10−10) of lithium and beryllium. Even smaller amounts of boron may have been produced in the Big Bang, since it has been observed in some very old stars, while carbon has not. [22] No elements heavier than boron were produced in the Big Bang. As a result, the primordial abundance of atoms (or ions) consisted of roughly 75% 1H, 25% 4He, and 0.01% deuterium, with only tiny traces of lithium, beryllium, and perhaps boron. [23] Subsequent enrichment of galactic halos occurred due to stellar nucleosynthesis and supernova nucleosynthesis. [24] However, the element abundance in intergalactic space can still closely resemble primordial conditions, unless it has been enriched by some means.

Periodic table showing the cosmogenic origin of each element in the Big Bang, or in large or small stars. Small stars can produce certain elements up to sulfur, by the alpha process. Supernovae are needed to produce "heavy" elements (those beyond iron and nickel) rapidly by neutron buildup, in the r-process. Certain large stars slowly produce other elements heavier than iron, in the s-process; these may then be blown into space in the off-gassing of planetary nebulae Nucleosynthesis periodic table.svg
Periodic table showing the cosmogenic origin of each element in the Big Bang, or in large or small stars. Small stars can produce certain elements up to sulfur, by the alpha process. Supernovae are needed to produce "heavy" elements (those beyond iron and nickel) rapidly by neutron buildup, in the r-process. Certain large stars slowly produce other elements heavier than iron, in the s-process; these may then be blown into space in the off-gassing of planetary nebulae

On Earth (and elsewhere), trace amounts of various elements continue to be produced from other elements as products of nuclear transmutation processes. These include some produced by cosmic rays or other nuclear reactions (see cosmogenic and nucleogenic nuclides), and others produced as decay products of long-lived primordial nuclides. [25] For example, trace (but detectable) amounts of carbon-14 (14C) are continually produced in the atmosphere by cosmic rays impacting nitrogen atoms, and argon-40 (40Ar) is continually produced by the decay of primordially occurring but unstable potassium-40 (40K). Also, three primordially occurring but radioactive actinides, thorium, uranium, and plutonium, decay through a series of recurrently produced but unstable radioactive elements such as radium and radon, which are transiently present in any sample of these metals or their ores or compounds. Three other radioactive elements, technetium, promethium, and neptunium, occur only incidentally in natural materials, produced as individual atoms by nuclear fission of the nuclei of various heavy elements or in other rare nuclear processes.

In addition to the 94 naturally occurring elements, several artificial elements have been produced by human nuclear physics technology. As of 2021, these experiments have produced all elements up to atomic number 118.


The following graph (note log scale) shows the abundance of elements in our Solar System. The table shows the twelve most common elements in our galaxy (estimated spectroscopically), as measured in parts per million, by mass. [26] Nearby galaxies that have evolved along similar lines have a corresponding enrichment of elements heavier than hydrogen and helium. The more distant galaxies are being viewed as they appeared in the past, so their abundances of elements appear closer to the primordial mixture. As physical laws and processes appear common throughout the visible universe, however, scientist expect that these galaxies evolved elements in similar abundance.

The abundance of elements in the Solar System is in keeping with their origin from nucleosynthesis in the Big Bang and a number of progenitor supernova stars. Very abundant hydrogen and helium are products of the Big Bang, but the next three elements are rare since they had little time to form in the Big Bang and are not made in stars (they are, however, produced in small quantities by the breakup of heavier elements in interstellar dust, as a result of impact by cosmic rays). Beginning with carbon, elements are produced in stars by buildup from alpha particles (helium nuclei), resulting in an alternatingly larger abundance of elements with even atomic numbers (these are also more stable). In general, such elements up to iron are made in large stars in the process of becoming supernovas. Iron-56 is particularly common, since it is the most stable element that can easily be made from alpha particles (being a product of decay of radioactive nickel-56, ultimately made from 14 helium nuclei). Elements heavier than iron are made in energy-absorbing processes in large stars, and their abundance in the universe (and on Earth) generally decreases with their atomic number.

The abundance of the chemical elements on Earth varies from air to crust to ocean, and in various types of life. The abundance of elements in Earth's crust differs from that in the Solar System (as seen in the Sun and heavy planets like Jupiter) mainly in selective loss of the very lightest elements (hydrogen and helium) and also volatile neon, carbon (as hydrocarbons), nitrogen and sulfur, as a result of solar heating in the early formation of the solar system. Oxygen, the most abundant Earth element by mass, is retained on Earth by combination with silicon. Aluminium at 8% by mass is more common in the Earth's crust than in the universe and solar system, but the composition of the far more bulky mantle, which has magnesium and iron in place of aluminium (which occurs there only at 2% of mass) more closely mirrors the elemental composition of the solar system, save for the noted loss of volatile elements to space, and loss of iron which has migrated to the Earth's core.

The composition of the human body, by contrast, more closely follows the composition of seawater—save that the human body has additional stores of carbon and nitrogen necessary to form the proteins and nucleic acids, together with phosphorus in the nucleic acids and energy transfer molecule adenosine triphosphate (ATP) that occurs in the cells of all living organisms. Certain kinds of organisms require particular additional elements, for example the magnesium in chlorophyll in green plants, the calcium in mollusc shells, or the iron in the hemoglobin in vertebrate animals' red blood cells.

Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers (the Oddo-Harkins rule), and (2) a general decrease in abundance as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae. SolarSystemAbundances.png
Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers (the Oddo-Harkins rule), and (2) a general decrease in abundance as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae.
Elements in our galaxyParts per million
by mass
Hydrogen 739,000
Helium 240,000
Oxygen 10,400
Carbon 4,600
Neon 1,340
Iron 1,090
Nitrogen 960
Silicon 650
Magnesium 580
Sulfur 440
Potassium 210
Nickel 100
Essential elements [27] [28] [29] [30] [31]
H He
  Quantity elements
  Essential trace elements
  Essentiality or function in mammals debated
  No evidence for biological action in mammals, but essential in some lower organisms.
(In the case of the lanthanides, the definition of an essential nutrient as being indispensable and irreplaceable is not completely applicable due to their extreme similarity. The stable early lanthanides La–Nd are known to stimulate the growth of various lanthanide-using organisms, and Sm–Gd show lesser effects for some such organisms. The later elements in the lanthanide series do not appear to have such effects.) [32]


Evolving definitions

The concept of an "element" as an indivisible substance has developed through three major historical phases: Classical definitions (such as those of the ancient Greeks), chemical definitions, and atomic definitions.

Classical definitions

Ancient philosophy posited a set of classical elements to explain observed patterns in nature. These elements originally referred to earth , water , air and fire rather than the chemical elements of modern science.

The term 'elements' (stoicheia) was first used by the Greek philosopher Plato in about 360 BCE in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a speculative treatise on chemistry. Plato believed the elements introduced a century earlier by Empedocles were composed of small polyhedral forms: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth). [33] [34]

Aristotle, c.350 BCE, also used the term stoicheia and added a fifth element called aether, which formed the heavens. Aristotle defined an element as:

Element – one of those bodies into which other bodies can decompose, and that itself is not capable of being divided into other. [35]

Chemical definitions

Robert Boyle

Portrait of Robert Boyle, c. 1740 Portret van Robert Boyle, RP-P-OB-4578 (cropped).jpg
Portrait of Robert Boyle, c.1740
Title page of The Sceptical Chymist, published in 1661 Sceptical chymist 1661 Boyle Title page AQ18 (3).jpg
Title page of The Sceptical Chymist, published in 1661

In 1661, in The Sceptical Chymist , Robert Boyle proposed his theory of corpuscularism which favoured the analysis of matter as constituted by irreducible units of matter (atoms) and, choosing to side with neither Aristotle's view of the four elements nor Paracelsus' view of three fundamental elements, left open the question of the number of elements. Boyle argued against a pre-determined number of elements—directly against Paracelsus' three principles (sulfur, mercury, and salt), indirectly against the "Aristotelian" elements (earth, water, air, and fire), for Boyle felt that the arguments against the former were at least as valid against the latter.

Much of what I am to deliver ... may be indifferently apply'd to the four Peripatetick Elements, and the three Chymical Principles ... the Chymical Hypothesis seeming to be much more countenanc'd by Experience then the other, it will be expedient to insist chiefly upon the disproving of that; especially since most of the Arguments that are imploy'd against it, may, by a little variation, be made ... at least as strongly against the less plausible, Aristotelian Doctrine. [36]

Then Boyle stated his own view in four propositions. In the first and second, he suggests that matter consists of particles, but that these particles may be difficult to separate. Boyle used the concept of "corpuscles"—or "atomes", [37] as he also called them—to explain how a limited number of elements could combine into a vast number of compounds.

Propos. I.... At the first Production of mixt Bodies, the Universal Matter whereof they ... consisted, was actually divided into little Particles. [38] ... The Generation ... and wasting of Bodies ... and ... the Chymical Resolutions of mixt Bodies, and ... Operations of ... Fires upon them ... manifest their consisting of parts very minute... Epicurus ... as you well know, supposes ... all ... Bodies ... to be produc'd by ... Atomes, moving themselves to and fro ... in the ... Infinite Vacuum. [39] ... Propos. II.... These minute Particles ... were ... associated into minute ... Clusters ... not easily dissipable into such Particles as compos'd them. [40] ... If we assigne to the Corpuscles, whereof each Element consists, a peculiar size and shape ... such ... Corpuscles may be mingled in such various Proportions, and ... connected so many ... wayes, that an almost incredible number of ... Concretes may be compos'd of them. [41]

Boyle explained that gold reacts with aqua regia, and mercury with nitric acid, sulfuric acid, and sulfur to produce various "compounds", and that they could be recovered from those compounds, just as would be expected of elements. Yet, Boyle did not consider gold, [42] mercury, [43] or lead [42] elements, but rather—together with wine [44] —"perfectly mixt bodies".

Quicksilver ... with Aqua fortis will be brought into a ... white Powder ... with Sulphur it will compose a blood-red ... Cinaber. And yet out of all these exotick Compounds, we may recover the very same running Mercury. [45] ... Propos. III.... From most of such mixt Bodies ... there may by the Help of the Fire, be actually obtain'd a determinate number (whether Three, Four or Five, or fewer or more) of Substances ... The Chymists are wont to call the Ingredients of mixt Bodies, Principles, as the Aristotelians name them Elements. ... Principles ... as not being compounded of any more primary Bodies: and Elements, in regard that all mix'd Bodies are compounded of them. [46]

Even though Boyle is largely regarded as the first modern chemist, The Sceptical Chymist still contains old ideas about the elements, alien to a modern viewpoint. Sulphur, for example, is not only the familiar yellow non-metal, but also an inflammable "spirit". [44]

Isaac Watts

Portrait of Isaac Watts by John Shury, c. 1830 Portrait of Isaac Watts, D.D..jpg
Portrait of Isaac Watts by John Shury, c.1830

In 1724, in his book Logick , the English minister and logician Isaac Watts enumerated the elements then recognized by chemists. Watts' list of elements included two of Paracelsus' principles (sulfur and salt) and two classical elements (earth and water) as well as "spirit". Watts did, however, note a lack of consensus among chemists. [47]

Elements are such Substances as cannot be resolved, or reduced, into two or more Substances of different Kinds. ... Followers of Aristotle made Fire, Air, Earth and Water to be the four Elements, of which all earthly Things were compounded; and they suppos'd the Heavens to be a Quintessence, or fifth sort of Body, distinct from all these : But, since experimental Philosophy ... have been better understood, this Doctrine has been abundantly refuted. The Chymists make Spirit, Salt, Sulphur, Water and Earth to be their five Elements, because they can reduce all terrestrial Things to these five :.. tho' they are not all agreed.

Antoine Lavoisier, Jöns Jakob Berzelius, and Dmitri Mendeleev

Mendeleev's 1869 periodic table: An experiment on a system of elements. Based on their atomic weights and chemical similarities. Mendeleev's 1869 periodic table.svg
Mendeleev's 1869 periodic table: An experiment on a system of elements. Based on their atomic weights and chemical similarities.

The first modern list of chemical elements was given in Antoine Lavoisier's 1789 Elements of Chemistry , which contained thirty-three elements, including light and caloric. [48] By 1818, Jöns Jakob Berzelius had determined atomic weights for forty-five of the forty-nine then-accepted elements. Dmitri Mendeleev had sixty-three elements in his periodic table of 1869.

Dmitri Mendeleev in 1897 DIMendeleevCab.jpg
Dmitri Mendeleev in 1897

From Boyle until the early 20th century, an element was defined as a pure substance that could not be decomposed into any simpler substance. Put another way, a chemical element cannot be transformed into other chemical elements by chemical processes. Elements during this time were generally distinguished by their atomic weights, a property measurable with fair accuracy by available analytical techniques.

Atomic definitions

Henry Moseley Henry Moseley.jpg
Henry Moseley

The 1913 discovery by English physicist Henry Moseley that the nuclear charge is the physical basis for an atom's atomic number, further refined when the nature of protons and neutrons became appreciated, eventually led to the current definition of an element based on atomic number (number of protons per atomic nucleus). The use of atomic numbers, rather than atomic weights, to distinguish elements has greater predictive value (since these numbers are integers), and also resolves some ambiguities in the chemistry-based view due to varying properties of isotopes and allotropes within the same element. Currently, IUPAC defines an element to exist if it has isotopes with a lifetime longer than the 10−14 seconds it takes the nucleus to form an electronic cloud. [49]

By 1914, eighty-seven elements were known, all naturally occurring (see Timeline of chemical element discoveries). The remaining naturally occurring elements were discovered or isolated in subsequent decades, and various additional elements have also been produced synthetically, with much of that work pioneered by Glenn T. Seaborg. In 1955, element 101 was discovered and named mendelevium in honor of D.I. Mendeleev, the first to arrange the elements in a periodic manner.

Discovery and recognition of various elements

Ten materials familiar to various prehistoric cultures are now known to be chemical elements: Carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and zinc. Three additional materials now accepted as elements, arsenic, antimony, and bismuth, were recognized as distinct substances prior to 1500 AD. Phosphorus, cobalt, and platinum were isolated before 1750.

Most of the remaining naturally occurring chemical elements were identified and characterized by 1900, including:

Elements isolated or produced since 1900 include:

Recently discovered elements

The first transuranium element (element with atomic number greater than 92) discovered was neptunium in 1940. Since 1999, claims for the discovery of new elements have been considered by the IUPAC/IUPAP Joint Working Party. As of January 2016, all 118 elements have been confirmed by IUPAC as being discovered. The discovery of element 112 was acknowledged in 2009, and the name copernicium and the atomic symbol Cn were suggested for it. [50] The name and symbol were officially endorsed by IUPAC on 19 February 2010. [51] The heaviest element that is believed to have been synthesized to date is element 118, oganesson, on 9 October 2006, by the Flerov Laboratory of Nuclear Reactions in Dubna, Russia. [10] [52] Tennessine, element 117 was the latest element claimed to be discovered, in 2009. [53] On 28 November 2016, scientists at the IUPAC officially recognized the names for the four newest chemical elements, with atomic numbers 113, 115, 117, and 118. [54] [55]

List of the 118 known chemical elements

The following sortable table shows the 118 known chemical elements.

Element Origin of name [56] [57] Group Period Block Standard
Ar°(E) [lower-alpha 1]
Density [lower-alpha 2] [lower-alpha 3] Melting point [lower-alpha 4] Boiling point [lower-alpha 5] Specific
[lower-alpha 6]
Electro­negativity [lower-alpha 7] Abundance
in Earth's
[lower-alpha 8]
Origin [lower-alpha 9] Phase at r.t. [lower-alpha 10]
Atomic number
Symbol Name(Da)(g/cm3)(K)(K)(J/g ·K)(mg/kg)
1H Hydrogen Greek elements hydro- and -gen, 'water-forming'11 s-block 1.00800.0000898814.0120.2814.3042.201400 primordial gas
2He Helium Greek hḗlios, 'sun'181s-block4.00260.0001785 [lower-alpha 11] 4.225.1930.008primordialgas
3Li Lithium Greek líthos, 'stone'12s-block6.940.534453.6915603.5820.9820primordial solid
4Be Beryllium Beryl, a mineral (ultimately from the name of Belur in southern India) [58] 22s-block9.01221.85156027421.8251.572.8primordialsolid
5B Boron Borax, a mineral (from Arabic bawraq , Middle Persian *bōrag)132 p-block 10.812.34234942001.0262.0410primordialsolid
6C Carbon Latin carbo, 'coal'142p-block12.0112.267>400043000.7092.55200primordialsolid
7N Nitrogen Greek nítron and -gen, 'niter-forming'152p-block14.0070.001250663.1577.361.043.0419primordialgas
8O Oxygen Greek oxy- and -gen, 'acid-forming'162p-block15.9990.00142954.3690.200.9183.44461000primordialgas
9F Fluorine Latin fluere, 'to flow'172p-block18.9980.00169653.5385.030.8243.98585primordialgas
10Ne Neon Greek néon, 'new'182p-block20.1800.000900224.5627.071.030.005primordialgas
11Na Sodium Coined by Humphry Davy who first isolated it, from English soda (specifically caustic soda), via Italian from Arabic ṣudāʕ 'headache'
 · Symbol Na is derived from Neo-Latin natrium , coined from German Natron , 'natron'
12Mg Magnesium Magnesia, a district of Eastern Thessaly in Greece 23s-block24.3051.73892313631.0231.3123300primordialsolid
13Al Aluminium Alumina, from Latin alumen (gen. aluminis), 'bitter salt, alum'133p-block26.9822.70933.4727920.8971.6182300primordialsolid
14Si Silicon Latin silex, 'flint' (originally silicium)143p-block28.0852.3290168735380.7051.9282000primordialsolid
15P Phosphorus Greek phōsphóros, 'light-bearing'153p-block30.9741.823317.305500.7692.191050primordialsolid
16S Sulfur Latin163p-block32.062.07388.36717.870.712.58350primordialsolid
17Cl Chlorine Greek chlōrós, 'greenish yellow'173p-block35.450.0032171.6239.110.4793.16145primordialgas
18Ar Argon Greek argós, 'idle' (because of its inertness)183p-block39.950.00178483.8087.300.523.5primordialgas
19K Potassium Neo-Latin potassa, 'potash', itself from pot and ash
 · Symbol K is derived from Neo-Latin kalium , from German
20Ca Calcium Latin calx, 'lime'24s-block40.0781.55111517570.6471.0041500primordialsolid
21Sc Scandium Latin Scandia, 'Scandinavia'34 d-block 44.9562.985181431090.5681.3622primordialsolid
22Ti Titanium Titans, the sons of the earth goddess of Greek mythology44d-block47.8674.506194135600.5231.545650primordialsolid
23V Vanadium Vanadis, an Old Norse name for the Scandinavian goddess Freyja 54d-block50.9426.11218336800.4891.63120primordialsolid
24Cr Chromium Greek chróma, 'colour'64d-block51.9967.15218029440.4491.66102primordialsolid
25Mn Manganese Corrupted from magnesia negra ; see § magnesium 74d-block54.9387.21151923340.4791.55950primordialsolid
26Fe Iron English, from Proto-Celtic *īsarnom ('iron'), from a root meaning 'blood'
 · Symbol Fe is derived from Latin ferrum
27Co Cobalt German Kobold , 'goblin'94d-block58.9338.90176832000.4211.8825primordialsolid
28Ni Nickel Nickel, a mischievous sprite of German miner mythology104d-block58.6938.908172831860.4441.9184primordialsolid
29Cu Copper English, from Latin cuprum , from Ancient Greek Kýpros 'Cyprus'114d-block63.5468.961357.7728350.3851.9060primordialsolid
30Zn Zinc Most likely from German Zinke , 'prong' or 'tooth', though some suggest Persian sang , 'stone'124d-block65.387.14692.8811800.3881.6570primordialsolid
31Ga Gallium Latin Gallia , 'France'134p-block69.7235.91302.914626730.3711.8119primordialsolid
32Ge Germanium Latin Germania , 'Germany'144p-block72.6305.3231211.4031060.322.011.5primordialsolid
33As Arsenic Middle English, from Middle French arsenic , from Greek arsenikón 'yellow arsenic' (influenced by arsenikós , 'masculine' or 'virile'), from a West Asian wanderword ultimately from Old Iranian *zarniya-ka, 'golden'154p-block74.9225.7271090 [lower-alpha 12] 8870.3292.181.8primordialsolid
34Se Selenium Greek selḗnē , 'moon'164p-block78.9714.814539580.3212.550.05primordialsolid
35Br Bromine Greek brômos , 'stench'174p-block79.9043.1028265.8332.00.4742.962.4primordial liquid
36Kr Krypton Greek kryptós , 'hidden'184p-block83.7980.003749115.79119.930.2483.001×10−4primordialgas
37Rb Rubidium Latin rubidus , 'deep red'15s-block85.4681.532312.469610.3630.8290primordialsolid
38Sr Strontium Strontian, a village in Scotland, where it was found25s-block87.622.64105016550.3010.95370primordialsolid
39Y Yttrium Ytterby, Sweden, where it was found; see also terbium, erbium, ytterbium 35d-block88.9064.472179936090.2981.2233primordialsolid
40Zr Zirconium Zircon, a mineral, from Persian zargun, 'gold-hued'45d-block91.2246.52212846820.2781.33165primordialsolid
41Nb Niobium Niobe, daughter of king Tantalus from Greek mythology; see also tantalum 55d-block92.9068.57275050170.2651.620primordialsolid
42Mo Molybdenum Greek molýbdaina , 'piece of lead', from mólybdos , 'lead', due to confusion with lead ore galena (PbS)65d-block95.9510.28289649120.2512.161.2primordialsolid
43Tc Technetium Greek tekhnētós , 'artificial'75d-block[97] [lower-alpha 1] 11243045381.9~ 3×10−9 from decay solid
44Ru Ruthenium Neo-Latin Ruthenia , 'Russia'85d-block101.0712.45260744230.2382.20.001primordialsolid
45Rh Rhodium Greek rhodóeis , 'rose-coloured', from rhódon , 'rose'95d-block102.9112.41223739680.2432.280.001primordialsolid
46Pd Palladium Pallas, an asteroid, considered a planet at the time105d-block106.4212.0231828.0532360.2442.200.015primordialsolid
47Ag Silver English, from a common Germanic root
 · Symbol Ag is derived from Latin argentum
48Cd Cadmium Neo-Latin cadmia , 'calamine', from King Kadmos, legendary founder of Thebes125d-block112.418.65594.2210400.2321.690.159primordialsolid
49In Indium Latin indicum , 'indigo', the blue colour found in its spectrum135p-block114.827.31429.7523450.2331.780.25primordialsolid
50Sn Tin English, from a common Germanic root
 · Symbol Sn is derived from Latin stannum
51Sb Antimony Latin antimonium , the origin of which is uncertain: folk etymologies suggest it is derived from Greek antí ('against') + mónos ('alone'), or Old French anti-moine , 'Monk's bane', but it could plausibly be from or related to Arabic ʾiṯmid , 'antimony', reformatted as a Latin word
 · Symbol Sb is derived from Latin stibium 'stibnite'
52Te Tellurium Latin tellus , 'the ground, earth'165p-block127.606.24722.6612610.2022.10.001primordialsolid
53I Iodine French iode , from Greek ioeidḗs , 'violet'175p-block126.904.933386.85457.40.2142.660.45primordialsolid
54Xe Xenon Greek xénon , neuter form of xénos 'strange, foreign'185p-block131.290.005894161.4165.030.1582.603×10−5primordialgas
55Cs Caesium Latin caesius , 'sky-blue'16s-block132.911.93301.599440.2420.793primordialsolid
56Ba Barium Greek barýs , 'heavy'26s-block137.333.51100021700.2040.89425primordialsolid
57La Lanthanum Greek lanthánein , 'to lie hidden'f-block groups6 f-block 138.916.162119337370.1951.139primordialsolid
58Ce Cerium Ceres, a dwarf planet, considered a planet at the timef-block groups6f-block140.126.770106837160.1921.1266.5primordialsolid
59Pr Praseodymium Greek prásios dídymos , 'green twin'f-block groups6f-block140.916.77120837930.1931.139.2primordialsolid
60Nd Neodymium Greek néos dídymos , 'new twin'f-block groups6f-block144.247.01129733470.191.1441.5primordialsolid
61Pm Promethium Prometheus, a figure in Greek mythologyf-block groups6f-block[145]7.26131532731.132×10−19from decaysolid
62Sm Samarium Samarskite, a mineral named after V. Samarsky-Bykhovets, Russian mine officialf-block groups6f-block150.367.52134520670.1971.177.05primordialsolid
63Eu Europium Europe f-block groups6f-block151.965.244109918020.1821.22primordialsolid
64Gd Gadolinium Gadolinite, a mineral named after Johan Gadolin, Finnish chemist, physicist and mineralogistf-block groups6f-block157.257.90158535460.2361.26.2primordialsolid
65Tb Terbium Ytterby, Sweden, where it was found; see also yttrium, erbium, ytterbium f-block groups6f-block158.938.23162935030.1821.21.2primordialsolid
66Dy Dysprosium Greek dysprósitos , 'hard to get'f-block groups6f-block162.508.540168028400.171.225.2primordialsolid
67Ho Holmium Neo-Latin Holmia, 'Stockholm'f-block groups6f-block164.938.79173429930.1651.231.3primordialsolid
68Er Erbium Ytterby, Sweden, where it was found; see also yttrium, terbium, ytterbium f-block groups6f-block167.269.066180231410.1681.243.5primordialsolid
69Tm Thulium Thule, the ancient name for an unclear northern locationf-block groups6f-block168.939.32181822230.161.250.52primordialsolid
70Yb Ytterbium Ytterby, Sweden, where it was found; see also yttrium, terbium, erbium f-block groups6f-block173.056.90109714690.1551.13.2primordialsolid
71Lu Lutetium Latin Lutetia', 'Paris'36d-block174.979.841192536750.1541.270.8primordialsolid
72Hf Hafnium Neo-Latin Hafnia, 'Copenhagen' (from Danish havn , harbour)46d-block178.4913.31250648760.1441.33primordialsolid
73Ta Tantalum King Tantalus, father of Niobe from Greek mythology; see also niobium 56d-block180.9516.69329057310.141.52primordialsolid
74W Tungsten Swedish tung sten , 'heavy stone'
 · Symbol W is from Wolfram, originally from Middle High German wolf-rahm 'wolf's foam' describing the mineral wolframite [59]
75Re Rhenium Latin Rhenus , 'Rhine'76d-block186.2121.02345958690.1371.97×10−4primordialsolid
76Os Osmium Greek osmḗ , 'smell'86d-block190.2322.59330652850.132.20.002primordialsolid
77Ir Iridium Iris, the Greek goddess of the rainbow96d-block192.2222.56271947010.1312.200.001primordialsolid
78Pt Platinum Spanish platina , 'little silver', from plata 'silver'106d-block195.0821.452041.440980.1332.280.005primordialsolid
79Au Gold English, from the same Proto-Indo-European root as 'yellow'
 · Symbol Au is derived from Latin aurum
80Hg Mercury Mercury, Roman god of commerce, communication, and luck, known for his speed and mobility
 · Symbol Hg is derived from its Latin name hydrargyrum , from Greek hydrárgyros , 'water-silver'
81Tl Thallium Greek thallós , 'green shoot or twig'136p-block204.3811.8557717460.1291.620.85primordialsolid
82Pb Lead English, from Proto-Celtic *ɸloudom, from a root meaning 'flow'
 · Symbol Pb is derived from Latin plumbum
2.33 (4+)
83Bi Bismuth German Wismut , via Latin and Arabic from Greek psimúthion , 'white lead'156p-block208.989.78544.718370.1222.020.009primordialsolid
84Po Polonium Latin Polonia , 'Poland', home country of Marie Curie, who discovered it166p-block[209] [lower-alpha 1] 9.19652712352.02×10−10from decaysolid
85At Astatine Greek ástatos , 'unstable', alluding to its lack of stable isotopes176p-block[210](8.91–8.95)5756102.23×10−20from decay unknown phase
86Rn Radon Radium emanation, originally the name of the isotope radon-222 186p-block[222]0.00973202211.30.0942.24×10−13from decaygas
87Fr Francium France, home country of discoverer Marguerite Perey 17s-block[223](2.48)281890>0.79 [60] ~ 1×10−18from decayunknown phase
88Ra Radium Coined in French by discoverer Marie Curie, from Latin radius , 'ray'27s-block[226]5.597320100.0940.99×10−7from decaysolid
89Ac Actinium Greek aktís , 'ray'f-block groups7f-block[227]10132334710.121.15.5×10−10from decaysolid
90Th Thorium Thor, the Scandinavian god of thunderf-block groups7f-block232.0411.7211550610.1131.39.6primordialsolid
91Pa Protactinium English prefix proto- (from Greek prôtos , 'first, before') + actinium, since actinium is produced through the radioactive decay of protactiniumf-block groups7f-block231.0415.37184143001.51.4×10−6from decaysolid
92U Uranium Uranus, the seventh planet in the Solar Systemf-block groups7f-block238.0319.11405.344040.1161.382.7primordialsolid
93Np Neptunium Neptune, the eighth planet in the Solar Systemf-block groups7f-block[237]20.4591742731.36 3×10−12from decaysolid
94Pu Plutonium Pluto, a dwarf planet in the Solar System, considered a planet at the timef-block groups7f-block[244]19.85912.535011.28 3×10−11from decaysolid
95Am Americium The Americas, where the element was first synthesised, by analogy with its homologue § europium f-block groups7f-block[243]12144928801.13 synthetic solid
96Cm Curium Pierre Curie and Marie Curie, French physicists and chemistsf-block groups7f-block[247]13.51161333831.28syntheticsolid
97Bk Berkelium Berkeley, California, where the element was first synthesisedf-block groups7f-block[247]14.78125929001.3syntheticsolid
98Cf Californium California, where the element was first synthesised in the LBNL laboratoryf-block groups7f-block[251]15.11173(1743) [lower-alpha 2] 1.3syntheticsolid
99Es Einsteinium Albert Einstein, German physicistf-block groups7f-block[252]8.841133(1269)1.3syntheticsolid
100Fm Fermium Enrico Fermi, Italian physicistf-block groups7f-block[257](9.7) [lower-alpha 2] (1125) [61]
(1800) [62]
1.3syntheticunknown phase
101Md Mendelevium Dmitri Mendeleev, Russian chemist who proposed the periodic table f-block groups7f-block[258](10.3)(1100)1.3syntheticunknown phase
102No Nobelium Alfred Nobel, Swedish chemist and engineerf-block groups7f-block[259](9.9)(1100)1.3syntheticunknown phase
103Lr Lawrencium Ernest Lawrence, American physicist37d-block[266](14.4)(1900)1.3syntheticunknown phase
104Rf Rutherfordium Ernest Rutherford, chemist and physicist from New Zealand47d-block[267](17)(2400)(5800)syntheticunknown phase
105Db Dubnium Dubna, Russia, where the element was discovered in the JINR laboratory57d-block[268](21.6)syntheticunknown phase
106Sg Seaborgium Glenn T. Seaborg, American chemist67d-block[269](23–24)syntheticunknown phase
107Bh Bohrium Niels Bohr, Danish physicist77d-block[270](26–27)syntheticunknown phase
108Hs Hassium Neo-Latin Hassia, 'Hesse', a state in Germany87d-block[269](27–29)syntheticunknown phase
109Mt Meitnerium Lise Meitner, Austrian physicist97d-block[278](27–28)syntheticunknown phase
110Ds Darmstadtium Darmstadt, Germany, where the element was first synthesised in the GSI laboratories107d-block[281](26–27)syntheticunknown phase
111Rg Roentgenium Wilhelm Conrad Röntgen, German physicist117d-block[282](22–24)syntheticunknown phase
112Cn Copernicium Nicolaus Copernicus, Polish astronomer127d-block[285](14.0)(283±11)(340±10) [lower-alpha 2] syntheticunknown phase
113Nh Nihonium Japanese Nihon , 'Japan', where the element was first synthesised in the Riken laboratories137p-block[286](16)(700)(1400)syntheticunknown phase
114Fl Flerovium Flerov Laboratory of Nuclear Reactions, part of JINR, where the element was synthesised; itself named after Georgy Flyorov, Russian physicist147p-block[289](11.4±0.3)(284±50) [lower-alpha 2] syntheticunknown phase
115Mc Moscovium Moscow, Russia, where the element was first synthesised in the JINR laboratories157p-block[290](13.5)(700)(1400)syntheticunknown phase
116Lv Livermorium Lawrence Livermore National Laboratory in Livermore, California 167p-block[293](12.9)(700)(1100)syntheticunknown phase
117Ts Tennessine Tennessee, United States, where Oak Ridge National Laboratory is located177p-block[294](7.1–7.3)(700)(883)syntheticunknown phase
118Og Oganesson Yuri Oganessian, Russian physicist187p-block[294](7)(325±15)(450±10)syntheticunknown phase
  1. 1 2 3 Standard atomic weight
    • '1.0080': abridged value, uncertainty ignored here
    • '[97]', [ ] notation: massnumber of most stable isotope
  2. 1 2 3 4 5 Values in ( ) brackets are predictions
  3. Density ( sources )
  4. Melting point in kelvin  (K) ( sources )
  5. Boiling point in kelvin  (K) ( sources )
  6. Heat capacity ( sources )
  7. Electronegativity by Pauling ( source )
  8. Abundance of elements in Earth's crust
  9. Primordial (=Earth's origin), from decay, or synthetic
  10. Phase at Standard state (25 °C [77 °F], 100 kPa)
  11. Helium melting point: helium does not solidify at a pressure of 1 bar (0.99 atm). Helium can only solidify at pressures above 25 atmosphere.
  12. Arsenic: element sublimes at one atmosphere of pressure.

See also

Related Research Articles

<span class="mw-page-title-main">Atomic number</span> Number of protons found in the nucleus of an atom

The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (np) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic number is also equal to the number of electrons.

<span class="mw-page-title-main">Atom</span> Smallest unit of a chemical element

Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper. Atoms with the same number of protons but a different number of neutrons are called isotopes of the same element.

<span class="mw-page-title-main">Synthetic element</span> Chemical elements that do not occur naturally

A synthetic element is one of 24 known chemical elements that do not occur naturally on Earth: they have been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; thus, they are called "synthetic", "artificial", or "man-made". The synthetic elements are those with atomic numbers 95–118, as shown in purple on the accompanying periodic table: these 24 elements were first created between 1944 and 2010. The mechanism for the creation of a synthetic element is to force additional protons into the nucleus of an element with an atomic number lower than 95. All known synthetic elements are unstable, but they decay at widely varying rates: the half-lives of their longest-lived isotopes range from microseconds to millions of years.

Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium remains small, so that the universe still has approximately the same composition.

<span class="mw-page-title-main">Period (periodic table)</span> Method of visualizing the relationship between elements

A period on the periodic table is a row of chemical elements. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, elements in the same group (column) have similar chemical and physical properties, reflecting the periodic law. For example, the halogens lie in the second-to-last group and share similar properties, such as high reactivity and the tendency to gain one electron to arrive at a noble-gas electronic configuration. As of 2022, a total of 118 elements have been discovered and confirmed.

<span class="mw-page-title-main">Nuclide</span> Atomic species

A nuclide is a class of atoms characterized by their number of protons, Z, their number of neutrons, N, and their nuclear energy state.

A period 2 element is one of the chemical elements in the second row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties.

The abundance of the chemical elements is a measure of the occurrence of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by mass fraction, by mole fraction, or by volume fraction. Volume fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is similar in value to molecular mole fraction for gas mixtures at relatively low densities and pressures, and ideal gas mixtures. Most abundance values in this article are given as mass fractions.

<span class="mw-page-title-main">Mass number</span> Number of heavy particles in the atomic nucleus

The mass number (symbol A, from the German word: Atomgewicht, "atomic weight"), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approximately equal to the atomic (also known as isotopic) mass of the atom expressed in atomic mass units. Since protons and neutrons are both baryons, the mass number A is identical with the baryon number B of the nucleus (and also of the whole atom or ion). The mass number is different for each isotope of a given chemical element, and the difference between the mass number and the atomic number Z gives the number of neutrons (N) in the nucleus: N = AZ.

<span class="mw-page-title-main">Carbon-12</span> Isotope of Carbon

Carbon-12 (12C) is the most abundant of the two stable isotopes of carbon, amounting to 98.93% of element carbon on Earth; its abundance is due to the triple-alpha process by which it is created in stars. Carbon-12 is of particular importance in its use as the standard from which atomic masses of all nuclides are measured, thus, its atomic mass is exactly 12 daltons by definition. Carbon-12 is composed of 6 protons, 6 neutrons, and 6 electrons.

<span class="mw-page-title-main">Helium-4</span> Isotope of helium

Helium-4 is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists of two protons and two neutrons.

<span class="mw-page-title-main">Isotopes of hydrogen</span> Hydrogen with different numbers of neutrons

Hydrogen (1H) has three naturally occurring isotopes, sometimes denoted 1
, 2
, and 3
. 1
and 2
are stable, while 3
has a half-life of 12.32(2) years. Heavier isotopes also exist, all of which are synthetic and have a half-life of less than one zeptosecond (10−21 s). Of these, 5
is the least stable, while 7
is the most.

Natural nitrogen (7N) consists of two stable isotopes: the vast majority (99.6%) of naturally occurring nitrogen is nitrogen-14, with the remainder being nitrogen-15. Thirteen radioisotopes are also known, with atomic masses ranging from 9 to 23, along with three nuclear isomers. All of these radioisotopes are short-lived, the longest-lived being nitrogen-13 with a half-life of 9.965(4) min. All of the others have half-lives below 7.15 seconds, with most of these being below 620 milliseconds. Most of the isotopes with atomic mass numbers below 14 decay to isotopes of carbon, while most of the isotopes with masses above 15 decay to isotopes of oxygen. The shortest-lived known isotope is nitrogen-10, with a half-life of 143(36) yoctoseconds, though the half-life of nitrogen-9 has not been measured exactly.

Although there are nine known isotopes of helium (2He), only helium-3 and helium-4 are stable. All radioisotopes are short-lived, the longest-lived being 6
with a half-life of 806.92(24) milliseconds. The least stable is 10
, with a half-life of 260(40) yoctoseconds, although it is possible that 2
may have an even shorter half-life.

<span class="mw-page-title-main">Nuclear binding energy</span> Minimum energy required to separate particles within a nucleus

Nuclear binding energy in experimental physics is the minimum energy that is required to disassemble the nucleus of an atom into its constituent protons and neutrons, known collectively as nucleons. The binding energy for stable nuclei is always a positive number, as the nucleus must gain energy for the nucleons to move apart from each other. Nucleons are attracted to each other by the strong nuclear force. In theoretical nuclear physics, the nuclear binding energy is considered a negative number. In this context it represents the energy of the nucleus relative to the energy of the constituent nucleons when they are infinitely far apart. Both the experimental and theoretical views are equivalent, with slightly different emphasis on what the binding energy means.

A table or chart of nuclides is a two-dimensional graph of isotopes of the elements, in which one axis represents the number of neutrons and the other represents the number of protons in the atomic nucleus. Each point plotted on the graph thus represents a nuclide of a known or hypothetical chemical element. This system of ordering nuclides can offer a greater insight into the characteristics of isotopes than the better-known periodic table, which shows only elements and not their isotopes. The chart of the nuclides is also known as the Segrè chart, after the Italian physicist Emilio Segrè.

<span class="mw-page-title-main">Isotope</span> Different atoms of the same element

Isotopes are distinct nuclear species of the same chemical element. They have the same atomic number and position in the periodic table, but differ in nucleon numbers due to different numbers of neutrons in their nuclei. While all isotopes of a given element have almost the same chemical properties, they have different atomic masses and physical properties.

<span class="mw-page-title-main">Nuclear transmutation</span> Conversion of an atom from one element to another

Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.


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Further reading