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Covalent radius

January 20, 2023

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.

In principle, the sum of the two covalent radii should equal the covalent bond length between two atoms, R(AB) = r(A) + r(B). Moreover, different radii can be introduced for single, double and triple bonds (r1, r2 and r3 below), in a purely operational sense. These relationships are certainly not exact because the size of an atom is not constant but depends on its chemical environment. For heteroatomic A–B bonds, ionic terms may enter. Often the polar covalent bonds are shorter than would be expected based on 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, which makes them useful.

The bond lengths R(AB) are measured by X-ray diffraction (more rarely, neutron diffraction on molecular crystals). Rotational spectroscopy can also give extremely accurate values of bond lengths. For homonuclear A–A bonds, Linus Pauling took the covalent radius to be half the single-bond length in the element, e.g. R(H–H, in H2) = 74.14 pm so rcov(H) = 37.07 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,[1] but the availability of large collections of bond lengths, which are more transferable, from the Cambridge Crystallographic Database[2][3] has rendered covalent radii obsolete in many situations.

Average radii

The values in the table below are based on a statistical analysis of more than 228,000 experimental bond lengths from the Cambridge Structural Database.[4] For carbon, values are given for the different hybridisations of the orbitals.

Covalent radii in pm from analysis of the Cambridge Structural Database, which contains about 1,030,000 crystal structures[4]
H   He
1   2
31(5)   28
Li Be   B C N O F Ne
3 4 Radius (standard deviation) / pm 5 6 7 8 9 10
128(7) 96(3)   84(3) sp3 76(1)
sp2 73(2)
sp  69(1)		 71(1) 66(2) 57(3) 58
Na Mg   Al Si P S Cl Ar
11 12   13 14 15 16 17 18
166(9) 141(7)   121(4) 111(2) 107(3) 105(3) 102(4) 106(10)
K Ca   Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
19 20   21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
203(12) 176(10)   170(7) 160(8) 153(8) 139(5) l.s. 139(5)
h.s. 161(8)		 l.s. 132(3)
h.s. 152(6)		 l.s. 126(3)
h.s. 150(7)		 124(4) 132(4) 122(4) 122(3) 120(4) 119(4) 120(4) 120(3) 116(4)
Rb Sr   Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
37 38   39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
220(9) 195(10) 190(7) 175(7) 164(6) 154(5) 147(7) 146(7) 142(7) 139(6) 145(5) 144(9) 142(5) 139(4) 139(5) 138(4) 139(3) 140(9)
Cs Ba * Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
55 56   71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
244(11) 215(11)   175(10) 187(8) 170(8) 162(7) 151(7) 144(4) 141(6) 136(5) 136(6) 132(5) 145(7) 146(5) 148(4) 140(4) 150 150
Fr Ra **
87 88
260 221(2)
 
  * La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
  57 58 59 60 61 62 63 64 65 66 67 68 69 70
  207(8) 204(9) 203(7) 201(6) 199 198(8) 198(6) 196(6) 194(5) 192(7) 192(7) 189(6) 190(10) 187(8)
  ** Ac Th Pa U Np Pu Am Cm
  89 90 91 92 93 94 95 96
  215 206(6) 200 196(7) 190(1) 187(1) 180(6) 169(3)

Radii for multiple bonds

A different approach is to make a self-consistent fit for all elements in a smaller set of molecules. This was done separately for single,[5] double,[6] and triple bonds[7] up to superheavy elements. Both experimental and computational data were used. The single-bond results are often similar to those of Cordero et al.[4] When they are different, the coordination numbers used can be different. This is notably the case for most (d and f) transition metals. Normally one expects that r1 > r2 > r3. Deviations may occur for weak multiple bonds, if the differences of the ligand are larger than the differences of R in the data used.

Note that elements up to atomic number 118 (oganesson) have now been experimentally produced and that there are chemical studies on an increasing number of them. The same, self-consistent approach was used to fit tetrahedral covalent radii for 30 elements in 48 crystals with subpicometer accuracy.[8]

Single-,[5] double-,[6] and triple-bond[7] covalent radii, determined using typically
400 experimental or calculated primary distances, R, per set.
H   He
1   2
32
-
-		   46
-
-
Li Be   B C N O F Ne
3 4 Radius / pm: 5 6 7 8 9 10
133
124
-		 102
90
85		 single-bond

double-bond

triple-bond

85
78
73		 75
67
60		 71
60
54		 63
57
53		 64
59
53		 67
96
-
Na Mg   Al Si P S Cl Ar
11 12   13 14 15 16 17 18
155
160
-		 139
132
127		   126
113
111		 116
107
102		 111
102
94		 103
94
95		 99
95
93		 96
107
96
K Ca   Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
19 20   21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
196
193
-		 171
147
133		   148
116
114 		136
117
108		 134
112
106		 122
111
103		 119
105
103		 116
109
102		 111
103
96		 110
101
101		 112
115
120		 118
120
- 		124
117
121		 121
111
114		 121
114
106		 116
107
107		 114
109
110		 117
121
108
Rb Sr   Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
37 38   39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
210
202
-		 185
157
139		   163
130
124 		154
127
121		 147
125
116		 138
121
113		 128
120
110		 125
114
103		 125
110
106		 120
117
112		 128
139
137		 136
144
- 		142
136
146		 140
130
132		 140
133
127		 136
128
121		 133
129
125		 131
135
122
Cs Ba * Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
55 56   71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
232
209
-		 196
161
149		   162
131
131 		152
128
122		 146
126
119		 137
120
115		 131
119
110		 129
116
109		 122
115
107		 123
112
110		 124
121
123		 133
142
- 		144
142
150		 144
135
137		 151
141
135		 145
135
129		 147
138
138		 142
145
133
Fr Ra ** Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
87 88   103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
223
218
-		 201
173
159		   161
141
- 		157
140
131		 149
136
126		 143
128
121		 141
128
119		 134
125
118		 129
125
113		 128
116
112		 121
116
118		 122
137
130		 136
-
-		 143
-
-		 162
-
-		 175
-
-		 165
-
-		 157
-
-
 
  * La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
  57 58 59 60 61 62 63 64 65 66 67 68 69 70
  180
139
139		 163
137
131		 176
138
128		 174
137
-		 173
135
-		 172
134
-		 168
134
-		 169
135
132		 168
135
-		 167
133
-		 166
133
-		 165
133
-		 164
131
-		 170
129
-
  ** Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No
  89 90 91 92 93 94 95 96 97 98 99 100 101 102
  186
153
140		 175
143
136		 169
138
129		 170
134
118		 171
136
116		 172
135
-		 166
135
-		 166
136
-		 168
139
-		 168
140
-		 165
140
-		 167
-
-		 173
139
-		 176
-
-

See also

References

  1. ^ Sanderson, R. T. (1983). "Electronegativity and Bond Energy". Journal of the American Chemical Society. 105 (8): 2259–2261. doi:10.1021/ja00346a026.
  2. ^ 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 (12): S1–S19. doi:10.1039/P298700000S1.
  3. ^ Orpen, A. Guy; Brammer, Lee; Allen, Frank H.; Kennard, Olga; Watson, David G.; Taylor, Robin (1989). "Supplement. Tables of bond lengths determined by X-ray and neutron diffraction. Part 2. Organometallic compounds and co-ordination complexes of the d- and f-block metals". Journal of the Chemical Society, Dalton Transactions (12): S1. doi:10.1039/DT98900000S1.
  4. ^ a b c Beatriz Cordero; Verónica Gómez; Ana E. Platero-Prats; Marc Revés; Jorge Echeverría; Eduard Cremades; Flavia Barragán; Santiago Alvarez (2008). "Covalent radii revisited". Dalton Trans. (21): 2832–2838. doi:10.1039/b801115j. PMID 18478144. S2CID 244110.
  5. ^ a b P. Pyykkö; M. Atsumi (2009). "Molecular Single-Bond Covalent Radii for Elements 1-118". Chemistry: A European Journal. 15 (1): 186–197. doi:10.1002/chem.200800987. PMID 19058281.
  6. ^ a b P. Pyykkö; M. Atsumi (2009). "Molecular Double-Bond Covalent Radii for Elements Li–E112". Chemistry: A European Journal. 15 (46): 12770–12779. doi:10.1002/chem.200901472. PMID 19856342.. Figure 3 of this paper contains all radii of refs. [5-7]. The mean-square deviation of each set is 3 pm.
  7. ^ a b P. Pyykkö; S. Riedel; M. Patzschke (2005). "Triple-Bond Covalent Radii". Chemistry: A European Journal. 11 (12): 3511–3520. doi:10.1002/chem.200401299. PMID 15832398.
  8. ^ P. Pyykkö (2012). "Refitted tetrahedral covalent radii for solids". Physical Review B. 85 (2): 024115, 7 p. Bibcode:2012PhRvB..85b4115P. doi:10.1103/PhysRevB.85.024115.

January 20, 2023
covalent, radius, covalent, radius, rcov, measure, size, atom, that, forms, part, covalent, bond, usually, measured, either, picometres, angstroms, with, principle, covalent, radii, should, equal, covalent, bond, length, between, atoms, moreover, different, ra. 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 A with 1 A 100 pm In principle the sum of the two covalent radii should equal the covalent bond length between two atoms R AB r A r B Moreover different radii can be introduced for single double and triple bonds r1 r2 and r3 below in a purely operational sense These relationships are certainly not exact because the size of an atom is not constant but depends on its chemical environment For heteroatomic A B bonds ionic terms may enter Often the polar covalent bonds are shorter than would be expected based on 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 which makes them useful The bond lengths R AB are measured by X ray diffraction more rarely neutron diffraction on molecular crystals Rotational spectroscopy can also give extremely accurate values of bond lengths For homonuclear A A bonds Linus Pauling took the covalent radius to be half the single bond length in the element e g R H H in H2 74 14 pm so rcov H 37 07 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 1 but the availability of large collections of bond lengths which are more transferable from the Cambridge Crystallographic Database 2 3 has rendered covalent radii obsolete in many situations Contents 1 Average radii 2 Radii for multiple bonds 3 See also 4 ReferencesAverage radii EditThe values in the table below are based on a statistical analysis of more than 228 000 experimental bond lengths from the Cambridge Structural Database 4 For carbon values are given for the different hybridisations of the orbitals Covalent radii in pm from analysis of the Cambridge Structural Database which contains about 1 030 000 crystal structures 4 H He1 231 5 28Li Be B C N O F Ne3 4 Radius standard deviation pm 5 6 7 8 9 10128 7 96 3 84 3 sp3 76 1 sp2 73 2 sp 69 1 71 1 66 2 57 3 58Na Mg Al Si P S Cl Ar11 12 13 14 15 16 17 18166 9 141 7 121 4 111 2 107 3 105 3 102 4 106 10 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36203 12 176 10 170 7 160 8 153 8 139 5 l s 139 5 h s 161 8 l s 132 3 h s 152 6 l s 126 3 h s 150 7 124 4 132 4 122 4 122 3 120 4 119 4 120 4 120 3 116 4 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54220 9 195 10 190 7 175 7 164 6 154 5 147 7 146 7 142 7 139 6 145 5 144 9 142 5 139 4 139 5 138 4 139 3 140 9 Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn55 56 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86244 11 215 11 175 10 187 8 170 8 162 7 151 7 144 4 141 6 136 5 136 6 132 5 145 7 146 5 148 4 140 4 150 150Fr Ra 87 88260 221 2 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb 57 58 59 60 61 62 63 64 65 66 67 68 69 70 207 8 204 9 203 7 201 6 199 198 8 198 6 196 6 194 5 192 7 192 7 189 6 190 10 187 8 Ac Th Pa U Np Pu Am Cm 89 90 91 92 93 94 95 96 215 206 6 200 196 7 190 1 187 1 180 6 169 3 Radii for multiple bonds EditA different approach is to make a self consistent fit for all elements in a smaller set of molecules This was done separately for single 5 double 6 and triple bonds 7 up to superheavy elements Both experimental and computational data were used The single bond results are often similar to those of Cordero et al 4 When they are different the coordination numbers used can be different This is notably the case for most d and f transition metals Normally one expects that r1 gt r2 gt r3 Deviations may occur for weak multiple bonds if the differences of the ligand are larger than the differences of R in the data used Note that elements up to atomic number 118 oganesson have now been experimentally produced and that there are chemical studies on an increasing number of them The same self consistent approach was used to fit tetrahedral covalent radii for 30 elements in 48 crystals with subpicometer accuracy 8 Single 5 double 6 and triple bond 7 covalent radii determined using typically 400 experimental or calculated primary distances R per set H He1 232 46 Li Be B C N O F Ne3 4 Radius pm 5 6 7 8 9 10133124 1029085 single bond double bondtriple bond 857873 756760 716054 635753 645953 6796 Na Mg Al Si P S Cl Ar11 12 13 14 15 16 17 18155160 139132127 126113111 116107102 11110294 1039495 999593 9610796K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36196193 171147133 148116114 136117108 134112106 122111103 119105103 116109102 11110396 110101101 112115120 118120 124117121 121111114 121114106 116107107 114109110 117121108Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54210202 185157139 163130124 154127121 147125116 138121113 128120110 125114103 125110106 120117112 128139137 136144 142136146 140130132 140133127 136128121 133129125 131135122Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn55 56 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86232209 196161149 162131131 152128122 146126119 137120115 131119110 129116109 122115107 123112110 124121123 133142 144142150 144135137 151141135 145135129 147138138 142145133Fr Ra Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og87 88 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118223218 201173159 161141 157140131 149136126 143128121 141128119 134125118 129125113 128116112 121116118 122137130 136 143 162 175 165 157 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb 57 58 59 60 61 62 63 64 65 66 67 68 69 70 180139139 163137131 176138128 174137 173135 172134 168134 169135132 168135 167133 166133 165133 164131 170129 Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No 89 90 91 92 93 94 95 96 97 98 99 100 101 102 186153140 175143136 169138129 170134118 171136116 172135 166135 166136 168139 168140 165140 167 173139 176 See also EditAtomic radii of the elements data page Ionization energy Electron affinity Electron configuration Periodic tableReferences Edit Sanderson R T 1983 Electronegativity and Bond Energy Journal of the American Chemical Society 105 8 2259 2261 doi 10 1021 ja00346a026 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 12 S1 S19 doi 10 1039 P298700000S1 Orpen A Guy Brammer Lee Allen Frank H Kennard Olga Watson David G Taylor Robin 1989 Supplement Tables of bond lengths determined by X ray and neutron diffraction Part 2 Organometallic compounds and co ordination complexes of the d and f block metals Journal of the Chemical Society Dalton Transactions 12 S1 doi 10 1039 DT98900000S1 a b c Beatriz Cordero Veronica Gomez Ana E Platero Prats Marc Reves Jorge Echeverria Eduard Cremades Flavia Barragan Santiago Alvarez 2008 Covalent radii revisited Dalton Trans 21 2832 2838 doi 10 1039 b801115j PMID 18478144 S2CID 244110 a b P Pyykko M Atsumi 2009 Molecular Single Bond Covalent Radii for Elements 1 118 Chemistry A European Journal 15 1 186 197 doi 10 1002 chem 200800987 PMID 19058281 a b P Pyykko M Atsumi 2009 Molecular Double Bond Covalent Radii for Elements Li E112 Chemistry A European Journal 15 46 12770 12779 doi 10 1002 chem 200901472 PMID 19856342 Figure 3 of this paper contains all radii of refs 5 7 The mean square deviation of each set is 3 pm a b P Pyykko S Riedel M Patzschke 2005 Triple Bond Covalent Radii Chemistry A European Journal 11 12 3511 3520 doi 10 1002 chem 200401299 PMID 15832398 P Pyykko 2012 Refitted tetrahedral covalent radii for solids Physical Review B 85 2 024115 7 p Bibcode 2012PhRvB 85b4115P doi 10 1103 PhysRevB 85 024115 Retrieved from https en wikipedia org w index php title Covalent radius amp oldid 1082400038, wikipedia, wiki, 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