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.
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.
Atomic radius
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 53 120 or 110 32 2 He helium 120 31 140 46 3 Li lithium 145 167 182 or 181 133 152 4 Be beryllium 105 112 153 102 85 112 5 B boron 85 87 192 85 73 6 C carbon 70 67 170 75 60 7 N nitrogen 65 56 155 71 54 8 O oxygen 60 48 152 63 53 9 F fluorine 50 42 147 64 53 10 Ne neon 160 38 154 67 11 Na sodium 180 190 227 155 186 12 Mg magnesium 150 145 173 139 127 160 13 Al aluminium 125 118 184 126 111 143 14 Si silicon 110 111 210 116 102 15 P phosphorus 100 98 180 111 94 16 S sulfur 100 88 180 103 95 17 Cl chlorine 100 79 175 99 93 18 Ar argon 71 71 188 96 96 19 K potassium 220 243 275 196 227 20 Ca calcium 180 194 231 171 133 197 21 Sc scandium 160 184 211 148 114 162 b 22 Ti titanium 140 176 136 108 147 23 V vanadium 135 171 134 106 134 b 24 Cr chromium 140 166 122 103 128 b 25 Mn manganese 140 161 119 103 127 b 26 Fe iron 140 156 116 102 126 b 27 Co cobalt 135 152 111 96 125 b 28 Ni nickel 135 149 163 110 101 124 b 29 Cu copper 135 145 140 112 120 128 b 30 Zn zinc 135 142 139 118 134 b 31 Ga gallium 130 136 187 124 121 135 c 32 Ge germanium 125 125 211 121 114 33 As arsenic 115 114 185 121 106 34 Se selenium 115 103 190 116 107 35 Br bromine 115 94 185 or 183 114 110 36 Kr krypton 88 202 117 108 37 Rb rubidium 235 265 303 210 248 38 Sr strontium 200 219 249 185 139 215 39 Y yttrium 180 212 163 124 180 b 40 Zr zirconium 155 206 154 121 160 41 Nb niobium 145 198 147 116 146 b 42 Mo molybdenum 145 190 138 113 139 b 43 Tc technetium 135 183 128 110 136 b 44 Ru ruthenium 130 178 125 103 134 b 45 Rh rhodium 135 173 125 106 134 b 46 Pd palladium 140 169 163 120 112 137 b 47 Ag silver 160 165 172 128 137 144 b 48 Cd cadmium 155 161 158 136 151 b 49 In indium 155 156 193 142 146 167 50 Sn tin 145 145 217 140 132 51 Sb antimony 145 133 206 140 127 52 Te tellurium 140 123 206 136 121 53 I iodine 140 115 198 133 125 54 Xe xenon 108 216 131 122 55 Cs caesium 260 298 343 232 265 56 Ba barium 215 253 268 196 149 222 57 La lanthanum 195 226 180 139 187 b 58 Ce cerium 185 210 163 131 181.8 c 59 Pr praseodymium 185 247 176 128 182.4 c 60 Nd neodymium 185 206 174 181.4 c 61 Pm promethium 185 205 173 183.4 c 62 Sm samarium 185 238 172 180.4 c 63 Eu europium 185 231 168 180.4 c 64 Gd gadolinium 180 233 169 132 180.4 c 65 Tb terbium 175 225 168 177.3 c 66 Dy dysprosium 175 228 167 178.1 c 67 Ho holmium 175 226 166 176.2 c 68 Er erbium 175 226 165 176.1 c 69 Tm thulium 175 222 164 175.9 c 70 Yb ytterbium 175 222 170 176 c 71 Lu lutetium 175 217 162 131 173.8 c 72 Hf hafnium 155 208 152 122 159 73 Ta tantalum 145 200 146 119 146 b 74 W tungsten 135 193 137 115 139 b 75 Re rhenium 135 188 131 110 137 b 76 Os osmium 130 185 129 109 135 b 77 Ir iridium 135 180 122 107 135.5 b 78 Pt platinum 135 177 175 123 110 138.5 b 79 Au gold 135 174 166 124 123 144 b 80 Hg mercury 150 171 155 133 151 b 81 Tl thallium 190 156 196 144 150 170 82 Pb lead 180 154 202 144 137 83 Bi bismuth 160 143 207 151 135 84 Po polonium 190 135 197 145 129 85 At astatine 127 202 147 138 86 Rn radon 120 220 142 133 87 Fr francium 348 88 Ra radium 215 283 201 159 89 Ac actinium 195 186 140 90 Th thorium 180 175 136 179 b 91 Pa protactinium 180 169 129 163 d 92 U uranium 175 186 170 118 156 e 93 Np neptunium 175 171 116 155 e 94 Pu plutonium 175 172 159 e 95 Am americium 175 166 173 b 96 Cm curium 176 166 174 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 131 105 Db dubnium 126 106 Sg seaborgium 121 107 Bh bohrium 119 108 Hs hassium 118 109 Mt meitnerium 113 110 Ds darmstadtium 112 111 Rg roentgenium 118 112 Cn copernicium 130 113 Nh nihonium 114 Fl flerovium 115 Mc moscovium 116 Lv livermorium 117 Ts tennessine 118 Og oganesson
See also Atomic radius Covalent radius (Single-, double- and triple-bond radii, up to the superheavy elements.) Ionic radius
Notes Difference between empirical and calculated data: Empirical data basically means, "originating in or based on observation or experience" or "relying on experience or observation alone often without due regard for system and theory data". It basically means that you measured it through physical observation, and a lot of experiments generating the same results. Although, note that the values are not calculated by a formula. However, often the empirical results then become an equation of estimation. Calculated data on the other hand are only based on theories. Such theoretical predictions are useful when there are no ways of measuring radii experimentally, if you want to predict the radius of an element that hasn't been discovered yet, or it has too short of a half-life. The radius of an atom is not a uniquely defined property and depends on the definition. Data derived from other sources with different assumptions cannot be compared. † to an accuracy of about 5 pm (b) 12 coordinate (c) gallium has an anomalous crystal structure (d) 10 coordinate (e) uranium, neptunium and plutonium have irregular structures Triple bond mean-square deviation 3pm.
References
Data is as quoted at http://www.webelements.com/ from these sources:
Covalent radii (single bond)
Metallic radius