The atomic radius of a chemical element is the distance from the center of the nucleus to the outermost shell of an electron. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Depending on the definition, the term may apply only to isolated atoms, or also to atoms in condensed matter, covalently bound in molecules, or in ionized and excited states; and its value may be obtained through experimental measurements, or computed from theoretical models. Under some definitions, the value of the radius may depend on the atom's state and context. [1]
Atomic radii vary in a predictable and explicable manner across the periodic table. For instance, the radii generally decrease rightward along each period (row) of the table, from the alkali metals to the noble gases; and increase down each group (column). The radius increases sharply between the noble gas at the end of each period and the alkali metal at the beginning of the next period. These trends of the atomic radii (and of various other chemical and physical properties of the elements) can be explained by the electron shell theory of the atom; they provided important evidence for the development and confirmation of quantum theory.
Note: All measurements given are in picometers (pm). For more recent data on covalent radii see Covalent radius. Just as atomic units are given in terms of the atomic mass unit (approximately the proton mass), the physically appropriate unit of length here is the Bohr radius, which is the radius of a hydrogen atom. The Bohr radius is consequently known as the "atomic unit of length". It is often denoted by a0 and is approximately 53 pm. Hence, the values of atomic radii given here in picometers can be converted to atomic units by dividing by 53, to the level of accuracy of the data given in this table.
atomic number | symbol | name | empirical † | Calculated | van der Waals | Covalent (single bond) | Covalent (triple bond) | Metallic |
---|---|---|---|---|---|---|---|---|
1 | H | hydrogen | 25 [2] | 53[ citation needed ] | 120 [3] or 110 [4] | 32 | ||
2 | He | helium | 120[ citation needed ] | 31 [5] | 140 [3] [4] | 46 | ||
3 | Li | lithium | 145 [2] | 167 [5] | 182 [3] or 181 [4] | 133 | 152 | |
4 | Be | beryllium | 105 [2] | 112 [5] | 153 [4] | 102 | 85 [6] | 112 |
5 | B | boron | 85 [2] | 87 [5] | 192 [4] | 85 | 73 [6] | |
6 | C | carbon | 70 [2] | 67 [5] | 170 [3] [4] | 75 | 60 [6] | |
7 | N | nitrogen | 65 [2] | 56 [5] | 155 [3] [4] | 71 | 54 [6] | |
8 | O | oxygen | 60 [2] | 48 [5] | 152 [3] [4] | 63 | 53 [6] | |
9 | F | fluorine | 50 [2] | 42 [5] | 147 [3] [4] | 64 | 53 [6] | |
10 | Ne | neon | 160[ citation needed ] [7] | 38 [5] | 154 [3] [4] | 67 | ||
11 | Na | sodium | 180 [2] | 190 [5] | 227 [3] [4] | 155 | 186 | |
12 | Mg | magnesium | 150 [2] | 145 [5] | 173 [3] [4] | 139 | 127 [6] | 160 |
13 | Al | aluminium | 125 [2] | 118 [5] | 184 [4] | 126 | 111 [6] | 143 |
14 | Si | silicon | 110 [2] | 111 [5] | 210 [3] [4] | 116 | 102 [6] | |
15 | P | phosphorus | 100 [2] | 98 [5] | 180 [3] [4] | 111 | 94 [6] | |
16 | S | sulfur | 100 [2] | 88 [5] | 180 [3] [4] | 103 | 95 [6] | |
17 | Cl | chlorine | 100 [2] | 79 [5] | 175 [3] [4] | 99 | 93 [6] | |
18 | Ar | argon | 71[ citation needed ] | 71 [5] | 188 [3] [4] | 96 | 96 [6] | |
19 | K | potassium | 220 [2] | 243 [5] | 275 [3] [4] | 196 | 227 | |
20 | Ca | calcium | 180 [2] | 194 [5] | 231 [4] | 171 | 133 [6] | 197 |
21 | Sc | scandium | 160 [2] | 184 [5] | 211[ citation needed ] | 148 | 114 [6] | 162 b |
22 | Ti | titanium | 140 [2] | 176 [5] | 136 | 108 [6] | 147 | |
23 | V | vanadium | 135 [2] | 171 [5] | 134 | 106 [6] | 134 b | |
24 | Cr | chromium | 140 [2] | 166 [5] | 122 | 103 [6] | 128 b | |
25 | Mn | manganese | 140 [2] | 161 [5] | 119 | 103 [6] | 127 b | |
26 | Fe | iron | 140 [2] | 156 [5] | 116 | 102 [6] | 126 b | |
27 | Co | cobalt | 135 [2] | 152 [5] | 111 | 96 [6] | 125 b | |
28 | Ni | nickel | 135 [2] | 149 [5] | 163 [3] | 110 | 101 [6] | 124 b |
29 | Cu | copper | 135 [2] | 145 [5] | 140 [3] | 112 | 120 [6] | 128 b |
30 | Zn | zinc | 135 [2] | 142 [5] | 139 [3] | 118 | 134 b | |
31 | Ga | gallium | 130 [2] | 136 [5] | 187 [3] [4] | 124 | 121 [6] | 135 c |
32 | Ge | germanium | 125 [2] | 125 [5] | 211 [4] | 121 | 114 [6] | |
33 | As | arsenic | 115 [2] | 114 [5] | 185 [3] [4] | 121 | 106 [6] | |
34 | Se | selenium | 115 [2] | 103 [5] | 190 [3] [4] | 116 | 107 [6] | |
35 | Br | bromine | 115 [2] | 94 [5] | 185 [3] or 183 [4] | 114 | 110 [6] | |
36 | Kr | krypton | 88 [5] | 202 [3] [4] | 117 | 108 [6] | ||
37 | Rb | rubidium | 235 [2] | 265 [5] | 303 [4] | 210 | 248 | |
38 | Sr | strontium | 200 [2] | 219 [5] | 249 [4] | 185 | 139 [6] | 215 |
39 | Y | yttrium | 180 [2] | 212 [5] | 163 | 124 [6] | 180 b | |
40 | Zr | zirconium | 155 [2] | 206 [5] | 154 | 121 [6] | 160 | |
41 | Nb | niobium | 145 [2] | 198 [5] | 147 | 116 [6] | 146 b | |
42 | Mo | molybdenum | 145 [2] | 190 [5] | 138 | 113 [6] | 139 b | |
43 | Tc | technetium | 135 [2] | 183 [5] | 128 | 110 [6] | 136 b | |
44 | Ru | ruthenium | 130 [2] | 178 [5] | 125 | 103 [6] | 134 b | |
45 | Rh | rhodium | 135 [2] | 173 [5] | 125 | 106 [6] | 134 b | |
46 | Pd | palladium | 140 [2] | 169 [5] | 163 [3] | 120 | 112 [6] | 137 b |
47 | Ag | silver | 160 [2] | 165 [5] | 172 [3] | 128 | 137 [6] | 144 b |
48 | Cd | cadmium | 155 [2] | 161 [5] | 158 [3] | 136 | 151 b | |
49 | In | indium | 155 [2] | 156 [5] | 193 [3] [4] | 142 | 146 [6] | 167 |
50 | Sn | tin | 145 [2] | 145 [5] | 217 [3] [4] | 140 | 132 [6] | |
51 | Sb | antimony | 145 [2] | 133 [5] | 206 [4] | 140 | 127 [6] | |
52 | Te | tellurium | 140 [2] | 123 [5] | 206 [3] [4] | 136 | 121 [6] | |
53 | I | iodine | 140 [2] | 115 [5] | 198 [3] [4] | 133 | 125 [6] | |
54 | Xe | xenon | 108 [5] | 216 [3] [4] | 131 | 122 [6] | ||
55 | Cs | caesium | 260 [2] | 298 [5] | 343 [4] | 232 | 265 | |
56 | Ba | barium | 215 [2] | 253 [5] | 268 [4] | 196 | 149 [6] | 222 |
57 | La | lanthanum | 195 [2] | 226[ citation needed ] | 180 | 139 [6] | 187 b | |
58 | Ce | cerium | 185 [2] | 210[ citation needed ] | 163 | 131 [6] | 181.8 c | |
59 | Pr | praseodymium | 185 [2] | 247 [5] | 176 | 128 [6] | 182.4 c | |
60 | Nd | neodymium | 185 [2] | 206 [5] | 174 | 181.4 c | ||
61 | Pm | promethium | 185 [2] | 205 [5] | 173 | 183.4 c | ||
62 | Sm | samarium | 185 [2] | 238 [5] | 172 | 180.4 c | ||
63 | Eu | europium | 185 [2] | 231 [5] | 168 | 180.4 c | ||
64 | Gd | gadolinium | 180 [2] | 233 [5] | 169 | 132 [6] | 180.4 c | |
65 | Tb | terbium | 175 [2] | 225 [5] | 168 | 177.3 c | ||
66 | Dy | dysprosium | 175 [2] | 228 [5] | 167 | 178.1 c | ||
67 | Ho | holmium | 175 [2] | 226 [5] | 166 | 176.2 c | ||
68 | Er | erbium | 175 [2] | 226 [5] | 165 | 176.1 c | ||
69 | Tm | thulium | 175 [2] | 222 [5] | 164 | 175.9 c | ||
70 | Yb | ytterbium | 175 [2] | 222 [5] | 170 | 176 c | ||
71 | Lu | lutetium | 175 [2] | 217 [5] | 162 | 131 [6] | 173.8 c | |
72 | Hf | hafnium | 155 [2] | 208 [5] | 152 | 122 [6] | 159 | |
73 | Ta | tantalum | 145 [2] | 200 [5] | 146 | 119 [6] | 146 b | |
74 | W | tungsten | 135 [2] | 193 [5] | 137 | 115 [6] | 139 b | |
75 | Re | rhenium | 135 [2] | 188 [5] | 131 | 110 [6] | 137 b | |
76 | Os | osmium | 130 [2] | 185 [5] | 129 | 109 [6] | 135 b | |
77 | Ir | iridium | 135 [2] | 180 [5] | 122 | 107 [6] | 135.5 b | |
78 | Pt | platinum | 135 [2] | 177 [5] | 175 [3] | 123 | 110 [6] | 138.5 b |
79 | Au | gold | 135 [2] | 174 [5] | 166 [3] | 124 | 123 [6] | 144 b |
80 | Hg | mercury | 150 [2] | 171 [5] | 155 [3] | 133 | 151 b | |
81 | Tl | thallium | 190 [2] | 156 [5] | 196 [3] [4] | 144 | 150 [6] | 170 |
82 | Pb | lead | 180[ citation needed ] | 154 [5] | 202 [3] [4] | 144 | 137 [6] | |
83 | Bi | bismuth | 160 [2] | 143 [5] | 207 [4] | 151 | 135 [6] | |
84 | Po | polonium | 190 [2] | 135 [5] | 197 [4] | 145 | 129 [6] | |
85 | At | astatine | 127 [5] | 202 [4] | 147 | 138 [6] | ||
86 | Rn | radon | 120 [5] | 220 [4] | 142 | 133 [6] | ||
87 | Fr | francium | 348 [4] | |||||
88 | Ra | radium | 215 [2] | 283 [4] | 201 | 159 [6] | ||
89 | Ac | actinium | 195 [2] | 186 | 140 [6] | |||
90 | Th | thorium | 180 [2] | 175 | 136 [6] | 179 b | ||
91 | Pa | protactinium | 180 [2] | 169 | 129 [6] | 163 d | ||
92 | U | uranium | 175 [2] | 186 [3] | 170 | 118 [6] | 156 e | |
93 | Np | neptunium | 175 [2] | 171 | 116 [6] | 155 e | ||
94 | Pu | plutonium | 175 [2] | 172 | 159 e | |||
95 | Am | americium | 175 [2] | 166 | 173 b | |||
96 | Cm | curium | 176[ citation needed ] | 166 | 174 b | |||
97 | Bk | berkelium | 170 b | |||||
98 | Cf | californium | 186±2 b | |||||
99 | Es | einsteinium | 186±2 b | |||||
100 | Fm | fermium | ||||||
101 | Md | mendelevium | ||||||
102 | No | nobelium | ||||||
103 | Lr | lawrencium | ||||||
104 | Rf | rutherfordium | 131 [6] | |||||
105 | Db | dubnium | 126 [6] | |||||
106 | Sg | seaborgium | 121 [6] | |||||
107 | Bh | bohrium | 119 [6] | |||||
108 | Hs | hassium | 118 [6] | |||||
109 | Mt | meitnerium | 113 [6] | |||||
110 | Ds | darmstadtium | 112 [6] | |||||
111 | Rg | roentgenium | 118 [6] | |||||
112 | Cn | copernicium | 130 [6] | |||||
113 | Nh | nihonium | ||||||
114 | Fl | flerovium | ||||||
115 | Mc | moscovium | ||||||
116 | Lv | livermorium | ||||||
117 | Ts | tennessine | ||||||
118 | Og | oganesson |
In atomic physics, the Bohr model or Rutherford–Bohr model of the atom, presented by Niels Bohr and Ernest Rutherford in 1913, consists of a small, dense nucleus surrounded by orbiting electrons. It is analogous to the structure of the Solar System, but with attraction provided by electrostatic force rather than gravity. In the history of atomic physics, it followed, and ultimately replaced, several earlier models, including Joseph Larmor's Solar System model (1897), Jean Perrin's model (1901), the cubical model (1902), Hantaro Nagaoka's Saturnian model (1904), the plum pudding model (1904), Arthur Haas's quantum model (1910), the Rutherford model (1911), and John William Nicholson's nuclear quantum model (1912). The improvement over the 1911 Rutherford model mainly concerned the new quantum mechanical interpretation introduced by Haas and Nicholson, but forsaking any attempt to explain radiation according to classical physics.
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science under natural sciences that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances. Chemistry also addresses the nature of chemical bonds in chemical compounds.
A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules, crystals, and other structures. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds, or through the sharing of electrons as in covalent bonds. The strength of chemical bonds varies considerably; there are "strong bonds" or "primary bonds" such as covalent, ionic and metallic bonds, and "weak bonds" or "secondary bonds" such as dipole–dipole interactions, the London dispersion force, and hydrogen bonding.
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full valence shell, corresponding to a stable electronic configuration. In organic chemistry, covalent bonding is much more common than ionic bonding.
The following outline is provided as an overview of and topical guide to chemistry:
Electronegativity, symbolized as χ, is the tendency for an atom of a given chemical element to attract shared electrons when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons. Electronegativity serves as a simple way to quantitatively estimate the bond energy, and the sign and magnitude of a bond's chemical polarity, which characterizes a bond along the continuous scale from covalent to ionic bonding. The loosely defined term electropositivity is the opposite of electronegativity: it characterizes an element's tendency to donate valence electrons.
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and molecule is often used when referring to polyatomic ions.
The covalent radius, rcov, is a measure of the size of an atom that forms part of one covalent bond. It is usually measured either in picometres (pm) or angstroms (Å), with 1 Å = 100 pm.
The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Four widely used definitions of atomic radius are: Van der Waals radius, ionic radius, metallic radius and covalent radius. Typically, because of the difficulty to isolate atoms in order to measure their radii separately, atomic radius is measured in a chemically bonded state; however theoretical calculations are simpler when considering atoms in isolation. The dependencies on environment, probe, and state lead to a multiplicity of definitions.
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
The van der Waals radius, rw, of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms were not simply points and to demonstrate the physical consequences of their size through the van der Waals equation of state.
Dilithium, Li2, is a strongly electrophilic, diatomic molecule comprising two lithium atoms covalently bonded together. Li2 is known in the gas phase. It has a bond order of 1, an internuclear separation of 267.3 pm and a bond energy of 102 kJ/mol or 1.06 eV in each bond. The electron configuration of Li2 may be written as σ2.
In atomic physics, a partial charge is a non-integer charge value when measured in elementary charge units. It is represented by the Greek lowercase delta (𝛿), namely 𝛿− or 𝛿+.
Relativistic quantum chemistry combines relativistic mechanics with quantum chemistry to calculate elemental properties and structure, especially for the heavier elements of the periodic table. A prominent example is an explanation for the color of gold: due to relativistic effects, it is not silvery like most other metals.
In chemistry, bond order is a formal measure of the multiplicity of a covalent bond between two atoms. As introduced by Linus Pauling, bond order is defined as the difference between the numbers of electron pairs in bonding and antibonding molecular orbitals.
Ionic radius, rion, is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice. Ionic radii are typically given in units of either picometers (pm) or angstroms (Å), with 1 Å = 100 pm. Typical values range from 31 pm (0.3 Å) to over 200 pm (2 Å).
The lanthanide contraction is the greater-than-expected decrease in atomic radii/ionic radii of the elements in the lanthanide series from atomic number 57, lanthanum, to 71, lutetium, which results in smaller than otherwise expected atomic radii/ionic radii for the subsequent elements starting with 72, hafnium. The term was coined by the Norwegian geochemist Victor Goldschmidt in his series "Geochemische Verteilungsgesetze der Elemente".
In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of the molecule.
The covalent radius of fluorine is a measure of the size of a fluorine atom; it is approximated at about 60 picometres.
Data is as quoted at http://www.webelements.com/ from these sources:
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.