11The covalent radius, rcov, is a measure of the size of atom that forms part of a covalent bond. It is measured either in picometres (pm) or Ã¥ngströms (Ã
), with 1 Ã
= 100 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 bonds 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.
Table of covalent radii
Z Symbol r (Ã
)
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 (sp3) 0.76(1)
C (sp2) 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