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A block of the periodic table is a set of elements unified by the atomic orbitals their valence electrons or vacancies lie in.The term appears to have been first used by Charles Janet. Each block is named after its characteristic orbital: s-block, p-block, d-block, f-block and g-block.
The block names (s, p, d, and f) are derived from the spectroscopic notation for the value of an electron's azimuthal quantum number: sharp (0), principal (1), diffuse (2), or fundamental (3). Succeeding notations proceed in alphabetical order, as g, h, etc., though elements that would belong in such blocks have not yet been found.
The division into blocks is justified by their distinctive nature: s is characterized, except in H and He, by highly electropositive metals; p by a range of very distinctive metals and non-metals, many of them essential to life; d by metals with multiple oxidation states; f by metals so similar that their separation is problematic. Useful statements about the elements can be made on the basis of the block they belong to and their position in it, for example highest oxidation state, density, melting point… Electronegativity is rather systematically distributed across and between blocks.
There is an approximate correspondence between this nomenclature of blocks, based on electronic configuration, and sets of elements based on chemical properties. The s-block and p-block together are usually considered main-group elements, the d-block corresponds to the transition metals, and the f-block corresponds to the inner transition metals and encompasses nearly all of the lanthanides (like lanthanum) and the actinides (like actinium).
The group 12 elements zinc, cadmium, and mercury are sometimes regarded as main group, rather than transition group, because they are chemically and physically more similar to the p-block elements than the other d-block elements. The group 3 elements are occasionally considered main group elements due to their similarities to the s-block elements. However, they remain d-block elements even when considered to be main group.
Groups (columns) in the f-block (between groups 2 and 3) are not numbered.
Helium is an s-block element, with its outer (and only) electrons in the 1s atomic orbital, although its chemical properties are more similar to the p-block noble gases in group 18 due to its full shell.
…Na, K, Mg and Ca are essential in biological systems. Some…other s-block elements are used in medicine (e.g. Li and Ba) and/or occur as minor but useful contaminants in Ca bio-minerals e.g. Sr…These metals display only one stable oxidation state [+1 or +2]. This enables [their]…ions to move around the cell without…danger of being oxidised or reduced.
Wilkins RG and Wilkins PC (2003)
The role of calcium and comparable cations in animal behaviour, RSC, Cambridge, p. 1
The s-block, with the s standing for "sharp" and azimuthal quantum number 0, is on the left side of the conventional periodic table and is composed of elements from the first two columns plus one element in the rightmost column, the nonmetals hydrogen and helium and the alkali metals (in group 1) and alkaline earth metals (group 2). Their general valence configuration is ns1–2. Helium is an s-element, but nearly always finds its place to the far right in group 18, above the p-element neon. Each row of the table has two s-elements.
The metals of the s-block (from the second period onwards) are mostly soft and have generally low melting and boiling points. Most impart colour to a flame.
Chemically, all s-elements except helium are highly reactive. Metals of the s-block are highly electropositive and often form essentially ionic compounds with nonmetals, especially with the highly electronegative halogen nonmetals.
The p-block, with the p standing for "principal" and azimuthal quantum number 1, is on the right side of the standard periodic table and encompasses elements in groups 13 to 18. Their general electronic configuration is ns2np1–6. Helium, though being the first element in group 18, is not included in the p-block. Each row of the table has a place for six p-elements except for the first row (which has none).
This block is the only one having all three types of elements: metals, nonmetals, and metalloids. The p-block elements can be described on a group-by-group basis as: group 13, the icosagens ; 14, the crystallogens ; 15, the pnictogens ; 16, the chalcogens ; 17, the halogens ; and 18, the helium group , composed of the noble gases (excluding helium) and oganesson. Alternatively, the p-block can be described as containing post-transition metals ; metalloids; reactive nonmetals including the halogens; and noble gases (excluding helium).
The p-block elements are unified by the fact that their valence (outermost) electrons are in the p orbital. The p orbital consists of six lobed shapes coming from a central point at evenly spaced angles. The p orbital can hold a maximum of six electrons, hence there are six columns in the p-block. Elements in column 13, the first column of the p-block, have one p-orbital electron. Elements in column 14, the second column of the p-block, have two p-orbital electrons. The trend continues this way until column 18, which has six p-orbital electrons.
The block is a stronghold of the octet rule in its first row, but elements in subsequent rows often display hypervalence. The p-block elements show variable oxidation states usually differing by multiples of two. The reactivity of elements in a group generally decreases downwards. (Helium breaks this trend in group 18 by being more reactive than neon, but since helium is actually an s-block element, the p-block portion of the trend remains intact.)
The bonding in between metals and nonmetals depends on the electronegativity difference. Ionicity is possible when the electronegativity difference is high enough (e.g. Li3N). Metals in high oxidation states tend to form covalent structures (e.g. WF6), as do the more noble metals (e.g. HgCl2). There are also some metal oxides displaying electrical (metallic) conductivity, like RuO2, ReO3, and IrO2.The metalloids tend to form either covalent compounds or alloys with metals.
The ... elements show a horizontal similarity in their physical and chemical properties as well as the usual vertical relationship. This horizontal similarity is so marked that the chemistry of the first ... series ... is often discussed separately from that of the second and third series, which are more similar to one another than to the first series.
Kneen WR, Rogers MJW, and Simpson P 1972
Chemistry: Facts, patterns, and principles, Addison-Wesley, London, pp. 487−489
The d-block, with the d standing for "diffuse" and azimuthal quantum number 2, is in the middle of the periodic table and encompasses elements from groups 3 to 12; it starts in the 4th period. Periods from the fourth onwards have a space for ten d-block elements. Most or all of these elements are also known as transition metals because they occupy a transitional zone in properties, between the strongly electropositive metals of groups 1 and 2, and the weakly electropositive metals of groups 13 to 16. Group 3 or group 12, while still counted as d-block metals, are sometimes not counted as transition metals because they do not show the chemical properties characteristic of transition metals as much, for example, multiple oxidation states and coloured compounds.
The d-block elements are all metals and most have one or more chemically active d-orbital electrons. Because there is a relatively small difference in the energy of the different d-orbital electrons, the number of electrons participating in chemical bonding can vary. The d-block elements have a tendency to exhibit two or more oxidation states, differing by multiples of one. The most common oxidation states are +2 and +3. Chromium, iron, molybdenum, ruthenium, tungsten, and osmium can have formal oxidation numbers as low as −4; iridium holds the singular distinction of being capable of achieving an oxidation state of +9.
The d-orbitals (four shaped as four-leaf clovers, and the fifth as a dumbbell with a ring around it) can contain up to five pairs of electrons.
Because of their complex electronic structure, the significant electron correlation effects, and the large relativistic contributions, the f-block elements are probably the most challenging group of elements for electronic structure theory.
Dolg M 2015 (ed.)
Computational methods in lanthanide and actinide chemistry, John Wiley & Sons, Chichester, p. xvii
The f-block, with the f standing for "fundamental" and azimuthal quantum number 3, appears as a footnote in a standard 18-column table but is located at the center-left of a 32-column full width table. Periods from the sixth onwards have a place for fourteen f-block elements. These elements are generally not considered part of any group. They are sometimes called inner transition metals because they provide a transition between the s-block and d-block in the 6th and 7th row (period), in the same way that the d-block transition metals provide a transitional bridge between the s-block and p-block in the 4th and 5th rows.
The f-block elements come in two series, in periods 6 and 7. All are metals. The f-orbital electrons are less active in the chemistry of the period 6 f-block elements, although they do make some contribution:these are rather similar to each other. They are more active in the early period 7 f-block elements, where the energies of the 5f, 7s, and 6d shells are quite similar; consequently these elements tend to show as much chemical variability as their transition metals analogues. The later period 7 f-block elements from about curium onwards behave more like their period 6 counterparts.
The f-block elements are unified by mostly having one or more electrons in an inner f-orbital. Of the f-orbitals, six have six lobes each, and the seventh looks like a dumbbell with a donut with two rings. They can contain up to seven pairs of electrons hence the block occupies fourteen columns in the periodic table. They are not assigned group numbers, since vertical periodic trends cannot be discerned in a "group" of two elements.
The two 14-member rows of the f-block elements are sometimes confused with the lanthanides and the actinides , which are names for sets of elements based on chemical properties more so than electron configurations. The lanthanides are the 15 elements running from lanthanum (La) to lutetium (Lu); the actinides are the 15 elements running from actinium (Ac) to lawrencium (Lr).
In many periodic tables, the f-block is shifted one element to the right, so that lanthanum and actinium become d-block elements, and Ce–Lu and Th–Lr form the f-block tearing the d-block into two very uneven portions. This is a holdover from early erroneous measurements of electron configurations in which the 4f shell was thought to complete its filling only at lutetium.In fact ytterbium completes the 4f shell, and on this basis Lev Landau and Evgeny Lifshitz considered in 1948 that lutetium cannot correctly be considered an f-block element. Since then, physical, chemical, and electronic evidence has overwhelmingly supported that the f-block contains the elements La–Yb and Ac–No, as shown here and as supported by International Union of Pure and Applied Chemistry reports dating from 1988 and 2021.
A g-block, with azimuthal quantum number 4, is predicted to begin in the vicinity of element 121. Though g-orbitals are not expected to start filling in the ground state until around element 124–126 (see extended periodic table), they are likely already low enough in energy to start participating chemically in element 121,similar to the situation of the 4f and 5f orbitals.
If the trend of the previous rows continued, then the g-block would have eighteen elements. However, calculations predict a very strong blurring of periodicity in the eighth period, to the point that individual blocks become hard to delineate. It is likely that the eighth period will not quite follow the trend of previous rows.
Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the rare earth elements. Like most other rare earth elements, the usual oxidation state is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.
The lanthanide or lanthanoid series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare-earth elements or rare-earth metals.
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of chemistry. It is a graphic formulation of the periodic law, which states that the properties of the chemical elements exhibit an approximate periodic dependence on their atomic numbers. The table is divided into four roughly rectangular areas called blocks. The rows of the table are called periods, and the columns are called groups. Elements from the same group of the periodic table show similar chemical characteristics. Trends run through the periodic table, with nonmetallic character increasing from left to right across a period, and from down to up across a group, and metallic character increasing in the opposite direction. The underlying reason for these trends is electron configurations of atoms. The periodic table exclusively lists electrically neutral atoms that have an equal number of positively charged protons and negatively charged electrons and puts isotopes at the same place. Other atoms, like nuclides and isotopes, are graphically collected in other tables like the tables of nuclides.
In chemistry, a transition metal is a chemical element in the d-block of the periodic table, though the elements of group 12 are sometimes excluded. The lanthanide and actinide elements are called inner transition metals and are sometimes considered to be transition metals as well.
In physics and chemistry, ionization energy (IE) (American English spelling), ionisation energy (British English spelling) is the minimum energy required to remove the most loosely bound electron of an isolated gaseous atom, positive ion, or molecule. The first ionization energy is quantitatively expressed as
In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals. For example, the electron configuration of the neon atom is 1s2 2s2 2p6, meaning that the 1s, 2s and 2p subshells are occupied by 2, 2 and 6 electrons respectively.
In chemistry, a group is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table; the 14 f-block columns, between groups 2 and 3, are not numbered. The elements in a group have similar physical or chemical characteristics of the outermost electron shells of their atoms, because most chemical properties are dominated by the orbital location of the outermost electron.
A period in 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.
In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases to shiny solids. The electrons in nonmetals behave differently from those in metals. With some exceptions, those in nonmetals are fixed in place, resulting in nonmetals usually being poor conductors of heat and electricity and brittle or crumbly when solid. The electrons in metals are generally free moving and this is why metals are good conductors and most are easily flattened into sheets and drawn into wires. Nonmetal atoms tend to attract electrons in chemical reactions and to form acidic compounds.
A period 6 element is one of the chemical elements in the sixth row (or period) of the periodic table of the elements, including the lanthanides. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The sixth period contains 32 elements, tied for the most with period 7, beginning with caesium and ending with radon. Lead is currently the last stable element; all subsequent elements are radioactive. For bismuth, however, its only primordial isotope, 209Bi, has a half-life of more than 1019 years, over a billion times longer than the current age of the universe. As a rule, period 6 elements fill their 6s shells first, then their 4f, 5d, and 6p shells, in that order; however, there are exceptions, such as gold.
A period 1 element is one of the chemical elements in the first row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate periodic (recurring) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that analog elements fall into the same vertical columns. The first period contains fewer elements than any other row in the table, with only two: hydrogen and helium. This situation can be explained by modern theories of atomic structure. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the 1s orbital. Period 1 elements obey the duet rule in that they need two electrons to complete their valence shell.
A period 7 element is one of the chemical elements in the seventh 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 begun when chemical behavior begins to repeat, meaning that elements with similar behavior fall into the same vertical columns. The seventh period contains 32 elements, tied for the most with period 6, beginning with francium and ending with oganesson, the heaviest element currently discovered. As a rule, period 7 elements fill their 7s shells first, then their 5f, 6d, and 7p shells in that order, but there are exceptions, such as uranium.
Chemistry is the physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.
The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The rule is especially applicable to carbon, nitrogen, oxygen, and the halogens; although more generally the rule is applicable for the s-block and p-block of the periodic table. Other rules exist for other elements, such as the duplet rule for hydrogen and helium, or the 18-electron rule for transition metals.
Group 3 is the first group of transition metals in the periodic table. This group is closely related to the rare-earth elements. It contains the four elements scandium (Sc), yttrium (Y), lutetium (Lu), and lawrencium (Lr). The group is also called the scandium group or scandium family after its lightest member.
In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair forms with both atoms in the bond each contributing one valence electron.
The periodic table is an arrangement of the chemical elements, structured by their atomic number, electron configuration and recurring chemical properties. In the basic form, elements are presented in order of increasing atomic number, in the reading sequence. Then, rows and columns are created by starting new rows and inserting blank cells, so that rows (periods) and columns (groups) show elements with recurring properties. For example, all elements in group (column) 18 are noble gases that are largely—though not completely—unreactive.
Alternative periodic tables are tabulations of chemical elements differing in their organization from the traditional depiction of the periodic system.
In nuclear chemistry, the actinide concept proposed that the actinides form a second inner transition series homologous to the lanthanides. Its origins stem from observation of lanthanide-like properties in transuranic elements in contrast to the distinct complex chemistry of previously known actinides. Glenn T. Seaborg, one of the researchers who synthesized transuranic elements, proposed the actinide concept in 1944 as an explanation for observed deviations and a hypothesis to guide future experiments. It was accepted shortly thereafter, resulting in the placement of a new actinide series comprising elements 89 (actinium) to 103 (lawrencium) below the lanthanides in Dmitri Mendeleev's periodic table of the elements.
Kainosymmetry describes the first atomic orbital of each azimuthal quantum number (ℓ). Such orbitals include 1s, 2p, 3d, 4f, 5g, and so on. The term kainosymmetric was coined by Sergey Shchukarev. Pekka Pyykkö referred to such orbitals as primogenic instead. Such orbitals are much smaller than all other orbitals with the same ℓ and have no radial nodes, giving the elements that fill them special properties. They are usually less metallic than their heavier homologues, prefer lower oxidation states, and have smaller atomic and ionic radii.
The tetrahedral periodic table of elements. Animation showing a transition from the conventional table into a tetrahedron.