Covalent radius 37706 212787340 2008-05-16T07:11:37Z Rjwilmsi 203434 Typo/date fixing using [[Project:AutoWikiBrowser|AWB]] {{Atomic radius}} The '''covalent radius''', ''r''<sub>cov</sub>, is a measure of the size of [[atom]] which forms part of a [[covalent bond]]. It is measured either in [[picometre]]s (pm) or [[ångström]]s (Å), with 1&nbsp;Å&nbsp;= 100&nbsp;pm. In principle, the sum of the two covalent radii should equal the covalent [[bond length]] between two atoms. This relationship does not hold exactly because the size of an atom is not constant but depends on its chemical environment. In particular, [[polar covalent bond]]s tend to be shorter than would be expected on the basis of the sum of covalent radii. Tabulated values of covalent radii are either average or idealized values, which nevertheless show a certain [[transferability]] between different situations. Covalent radii are measured by [[X-ray diffraction]] (more rarely, [[neutron diffraction]] on [[molecular crystal]]s). [[Rotational spectroscopy]] can also give extremely accurate values of bond lengths. One method takes the covalent radius to be half the single bond length in the element, e.g. ''d''(H&ndash;H, in H<sub>2</sub>)&nbsp;= 74.14&nbsp;pm so ''r''<sub>cov</sub>(H)&nbsp;= 37.07&nbsp;pm: in practice, it is usual to obtain an average value from a variety of covalent compounds, although the difference is usually small. Sanderson has published a recent set of non-polar covalent radii for the main-group elements,<ref>Sanderson, R. T. (1983). "Electronegativity and Bond Energy." [[Journal of the American Chemical Society|''J. Am. Chem. Soc.'']] '''105''':2259&ndash;61.</ref> but the availability of large collections of bond lengths, which are more [[Transferability|transferable]], from the [[Cambridge Crystallographic Database]]<ref>Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. (1987). "Table of Bond Lengths Determined by X-Ray and Neutron Diffraction." ''[[J. Chem. Soc., Perkin Trans. 2]]'' S1&ndash;S19.</ref> has rendered covalent radii obsolete in many situations. ==Table of covalent radii== The values in this table are based on a statistical analysis of more than 228,000 experimental bond lengths from the Cambridge Structural Database.<ref>Beatriz Cordero, Verónica Gómez, Ana E. Platero-Prats, Marc Revés, Jorge Echeverría, Eduard Cremades, Flavia Barragán and Santiago Alvarez. Covalent radii revisited. ''Dalton Trans.'', '''2008''', 2832-2838, {{doi|10.1039/b801115j}}</ref> The numbers in parentheses are the estimated standard deviations for the last digit. {| class="wikitable" ! Z !! Symbol !! r (Å) |- | 1 || H || 0.31(5) |- | 2 || He || 0.28 |- | 3 || Li || 1.28(7) |- | 4 || Be || 0.96(3) |- | 5 || B || 0.84(3) |- | 6 || C (sp<sup>3</sup>) || 0.76(1) |- | || C (sp<sup>2</sup>) || 0.73(2) |- | || C (sp) || 0.69(1) |- | 7 || N || 0.71(1) |- | 8 || O || 0.66(2) |- | 9 || F || 0.57(3) |- | 10 || Ne || 0.58 |- | 11 || Na || 1.66(9) |- | 12 || Mg || 1.41(7) |- | 13 || Al || 1.21(4) |- | 14 || Si || 1.11(2) |- | 15 || P || 1.07(3) |- | 16 || S || 1.05(3) |- | 17 || Cl || 1.02(4) |- | 18 || Ar || 1.06(10) |- | 19 || K || 2.03(12) |- | 20 || Ca || 1.76(10) |- | 21 || Sc || 1.70(7) |- | 22 || Ti || 1.60(8) |- | 23 || V || 1.53(8) |- | 24 || Cr || 1.39(5) |- | 25 || Mn (low spin) || 1.39(5) |- | || Mn (high spin) || 1.61(8) |- | 26 || Fe (low spin) || 1.32(3) |- | || Fe (high spin) || 1.52(6) |- | 27 || Co (low spin) || 1.26(3) |- | || Co (high spin) || 1.50(7) |- | 28 || Ni || 1.24(4) |- | 29 || Cu || 1.32(4) |- | 30 || Zn || 1.22(4) |- | 31 || Ga || 1.22(3) |- | 32 || Ge || 1.20(4) |- | 33 || As || 1.19(4) |- | 34 || Se || 1.20(4) |- | 35 || Br || 1.20(3) |- | 36 || Kr || 1.16(4) |- | 37 || Rb || 2.20(9) |- | 38 || Sr || 1.95(10) |- | 39 || Y || 1.90(7) |- | 40 || Zr || 1.75(7) |- | 41 || Nb || 1.64(6) |- | 42 || Mo || 1.54(5) |- | 43 || Tc || 1.47(7) |- | 44 || Ru || 1.46(7) |- | 45 || Rh || 1.42(7) |- | 46 || Pd || 1.39(6) |- | 47 || Ag || 1.45(5) |- | 48 || Cd || 1.44(9) |- | 49 || In || 1.42(5) |- | 50 || Sn || 1.39(4) |- | 51 || Sb || 1.39(5) |- | 52 || Te || 1.38(4) |- | 53 || I || 1.39(3) |- | 54 || Xe || 1.40(9) |- | 55 || Cs || 2.44(11) |- | 56 || Ba || 2.15(11) |- | 57 || La || 2.07(8) |- | 58 || Ce || 2.04(9) |- | 59 || Pr || 2.03(7) |- | 60 || Nd || 2.01(6) |- | 61 || Pm || 1.99 |- | 62 || Sm || 1.98(8) |- | 63 || Eu || 1.98(6) |- | 64 || Gd || 1.96(6) |- | 65 || Tb || 1.94(5) |- | 66 || Dy || 1.92(7) |- | 67 || Ho || 1.92(7) |- | 68 || Er || 1.89(6) |- | 69 || Tm || 1.90(10) |- | 70 || Yb || 1.87(8) |- | 71 || Lu || 1.87(8) |- | 72 || Hf || 1.75(10) |- | 73 || Ta || 1.70(8) |- | 74 || W || 1.62(7) |- | 75 || Re || 1.51(7) |- | 76 || Os || 1.44(4) |- | 77 || Ir || 1.41(6) |- | 78 || Pt || 1.36(5) |- | 79 || Au || 1.36(6) |- | 80 || Hg || 1.32(5) |- | 81 || Tl || 1.45(7) |- | 82 || Pb || 1.46(5) |- | 83 || Bi || 1.48(4) |- | 84 || Po || 1.40(4) |- | 85 || At || 1.50 |- | 86 || Rn || 1.50 |- | 87 || Fr || 2.60 |- | 88 || Ra || 2.21(2) |- | 89 || Ac || 2.15 |- | 90 || Th || 2.06(6) |- | 91 || Pa || 2.00 |- | 92 || U || 1.96(7) |- | 93 || Np || 1.90(1) |- | 94 || Pu || 1.87(1) |- | 95 || Am || 1.80(6) |- | 96 || Cm || 1.69(3) |} == References == <references/> [[Category:Chemical properties]] [[Category:Chemical bonding]] [[ar:نصف قطر تساهمي]] [[ast:Radiu covalente]] [[ca:Radi covalent]] [[cs:Kovalentní poloměr]] [[de:Kovalenter Radius]] [[es:Radio covalente]] [[eo:Kovalenta radiuso]] [[eu:Erradio kobalente]] [[fr:Rayon de covalence]] [[ko:공유 반지름]] [[it:Raggio covalente]] [[lt:Kovalentinis spindulys]] [[hu:Kovalens sugár]] [[mk:Ковалентен радиус]] [[nl:Covalente straal]] [[ja:共有結合半径]] [[no:Kovalent radius]] [[nn:Kovalent radius]] [[uz:Kovalentlik radiusi]] [[pl:Promień walencyjny]] [[pt:Raio covalente]] [[ru:Ковалентный радиус]] [[sl:Kovalentni polmer]] [[sr:Ковалентни радијус]] [[sh:Kovalentni radijus]] [[fi:Kovalenttinen säde]] [[sv:Kovalent radie]] [[th:รัศมีโควาเลนต์]] [[uk:Ковалентний радіус]] [[zh:共价半径]]