Atomic & Ionic Radii and Valence States of Chemical Elements
- Practical Electron Microscopy and Database -
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The radii of atoms and ions are defied by the maximum radial charge densities of their outermost electron shells. Their sizes vary and are difficult to quantify and measure.

Table 3131. Periodic table for ionic radii (pm) of chemical elements (Atomic Radius = AR, Covalent Radius = 0, positively and negatively charged Ionic Radius = +/-, High Spin = HS, Low Spin = LS, Square Planar = SQ, and Coordination Number 2 = CN2; … Coordination Number 14 = CN14 for the ions with the same charges).

1 2   3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
 
1 H
Hydrogen
AR = 79
0 = 32
-1 = 154
 
  2 He
Helium
AR = 128


 
3 Li
Lithium
AR = 152
0 = 163
+1 = 78: [CN4=73; CN6=90; CN8=106]
 
4 Be
Beryllium
AR = 111
0 = 90
+2 = 31: [CN4=41; CN6=59]

 
  5 B
Boron
AR = 98
0 = 82
+3 = 23: [CN4=23]


 

6 C
Carbon
AR = 91
0 = 77
+4 = 16: [CN4=29]
-4 = 260



7 N
Nitrogen
AR = 92
0 = 75
+5 = 13
-3 = 171: [CN4=132]

 

8 O
Oxygen
AR = 73
0 = 73
-2 = 140: [CN2=121; CN4=124; CN6=126; CN8=128]
9 F
Fluorine
AR = 64
0 = 72
-1 = 133: [CN2=115; CN4=117; CN6=119]


10 Ne
Neon
AR = 38
0 = 71


 

 
   
11 Na
Sodium
AR = 186
0 = 154
+1 = 95:[CN4=113; CN6=116; CN8=132; CN12=153]

12 Mg
Magnesium
AR = 160
0 = 136
+2 = 66: [CN4=71; CN6=86; CN8=103]
 

13 Al
Aluminium
AR = 143
0 = 118
+3 = 50: [CN4=53; CN6=68]

 

14 Si
Silicon
AR = 132
0 = 111
+4 = 41: [CN4=40; CN6=54]
-4 = 271
 
15 P
Phosphorus
AR = 128
0 = 106
+3 = 58: [CN6=58]
+5 = 35: [CN4=17; CN6=38]
-3 = 212
 

16 S
Sulphur
AR = 104
0 = 102
+6 = 30: [CN4=12; CN6=29]
-2 = 184: [CN4=184; CN6=190]

 

17 Cl
Chlorine
AR = 99
0 = 99
-1 = 181: [CN6=167]


 

18 Ar
Argon
AR = 71
0 = 98




 
 
19 K
Potassium
AR = 235
0 = 203
+1 = 133: [CN4=151; CN6=152; CN8=165; CN10=173; CN12=178]

 

20 Ca
Calcium
AR = 197
0 = 174
+2 = 99: [CN6=114; CN8=126; CN10=137; CN12=148]


 
  21 Sc
Scandium
AR = 162
0 = 144
+2 = 81
+3 = 88.5: [CN6=89; CN8=101]


 


 
22 Ti
Titanium
AR = 147
0 = 132
+2 = 91: [CN6=100]
+3 = 76: [CN6=81]
+4 = 74.5: [CN4=56; CN6=75; CN8=88]
23 V
Vanadium
AR = 134
0 = 122
+2 = 88: [CN6=75]
+3 = 74: [CN6=78]
+4 = 72
+5 = 68

 
24 Cr
Chromium
AR = 130
0 = 118
+2 = 84: [HS:CN6=94] [LS:CN6=87]
+3 = 69: [CN6=76]
+4 = 68
+5 = 63
+6 = 58

25 Mn
Manganese
AR = 135
0 = 117
+2 = 80: [HS:CN4=80; HS:CN6=97; LS: CN6=81]
+3 = 66: [HS: CN6=79; LS: CN6=72]
+7 = 60
26 Fe
Iron
AR = 126
0 = 117
+2 = 76: [HS:CN4=77; HS:CN6=92; LS:CN6=75]
+3 = 64: [HS:CN4=63; HS:CN6=79; LS:CN6=69]
27 Co
Cobalt
AR = 125
0 = 116
+2 = 76: [HS:CN4=72; HS:CN6=89; LS:CN6=79]
+3 = 63: [HS:CN6=75; LS:CN6=69]


28 Ni
Nickel
AR = 124
0 = 115
+2 = 72: [CN4=69; CN6=83; SQ:CN4=63]
+3: [HS:CN6=74; LS:CN6=70]


29 Cu
Copper
AR = 128
0 = 117
+1 = 91: [CN2=60; CN4=74; CN6=91]
+2 = 69: [CN4=71; CN6=87]


30 Zn
Zinc
AR = 138
0 = 125
+2 = 74: [CN4=74; CN6=88; CN8=104]


 


31 Ga
Gallium
AR = 141
0 = 126
+1 = 81
+3 = 62: [CN4=61; CN6=76]


 
 

32 Ge
Germanium
AR = 137
0 = 122
+2 = 73
+4 = 53: [CN4=53; CN6=67]



 
33 As
Arsenic
AR = 139
0 = 120
+5 = 46: [CN4=48; CN6=60]
-3 = 222
: [CN6=72]


 

34 Se
Selenium
AR = 117
0 = 116
+6 = 42
-2 = 198: [CN6=184]


 

 

35 Br
Bromine
AR = 114
0 = 114
+5 = 47
-1 = 196: [CN6=182]


 

 

36 Kr
Krypton
AR = 88
0 = 112



 


 


 
 
37 Rb
Rubidium
AR = 248
0 = 216
+1 = 148: [CN6=166; CN8=175; CN10=180; CN12=186; CN14=197]

 

38 Sr
Strontium
AR = 215
0 = 191
+2 = 112: [CN6=132; CN8=140; CN10=150; CN12=158]


 
  39 Y
Yttrium
AR = 178
0 = 162
+3 = 104: [CN6=104]


 
 

 

40 Zr
Zirconium
AR = 160
0 = 145
+4 = 86: [CN4=73; CN6=86; CN8=98]

 

 

41 Nb
Niobium
AR = 146
0 = 134
+3 = 86: [CN6=86]
+4 = 82: [CN6=82; CN8=93]
+5 = 78

 

42 Mo
Molybdenum
AR = 139
0 = 130
+3 = 83: [CN6=83]
+4 = 79: [CN6=79]
+5 = 75
+6 = 73

 

43 Tc
Technetium
AR = 136
0 = 127
+4 = 78.5: [CN6=79]
+5 = 74
+7 = 70

 

 

44 Ru
Ruthenium
AR = 134
0 = 125
+3 = 82: [CN6=82]
+4 = 76: [CN6=76]
+5 = 70.5


 

45 Rh
Rhodium
AR = 134
0 = 125
+3 = 80.5: [CN6=81]
+4 = 74: [CN6=74]
+5 = 69

 


46 Pd
Palladium
AR = 137
0 = 128
+2 = 100: [SQ:CN4=78; CN6=100]
+3 = 90
+4 = 75.5


 

47 Ag
Silver
AR = 144
0 = 134
+1 = 129: [CN2=81; CN4=114; SQ:CN4=116; CN6=129; CN8=142]
+2 = 108

+3 = 89
48 Cd
Cadmium
AR = 154
0 = 148
+2 = 109: [CN4=92; CN6=109; CN8=124; CN12=145]


 

49 In
Indium
AR = 166
0 = 144
+3 = 81: [CN4=76; CN6=94; CN8=106]



 
50 Sn
Tin
AR = 162
0 = 141
+2 = 93
+4 = 71: [CN4=69; CN6=83; CN8=95]


 

51 Sb
Antimony
AR = 159
0 = 140
+3: [CN6=90]
+6 = 62
-3 = 245
 


 

52 Te
Tellurium
AR = 143
0 = 136
+6 = 56
-2 = 221: [CN6=207]


 

 

53 I
Iodine
AR = 133
0 = 133
+7 = 50
-1 = 220: [CN6=206]


 

 

54 Xe
Xenon
AR = 108
0 = 131




 


 
 
55 Cs
Cesium
AR = 267
0 = 235
+1 = 170: [CN6=181; CN8=188; CN10=195; CN12=202]



 


 
56 Ba
Barium
AR = 222
0 = 198
+2 = 134: [CN6=149; CN8=156; CN10=166; CN12=175]

 



 
{57-70}
Lanthanoid
71 Lu
Lutetium
AR = 175
0 = 156
+3 = 85: [CN6=100; CN8=112]

 


 

 

72 Hf
Hafnium
AR = 167
0 = 144
+3 = 90
+4 = 85: [CN4=72; CN6=85; CN8=97]

 



 
73 Ta
Tantalum
AR = 149
0 = 134
+3 = 86: [CN6=86]
+4 = 82: [CN6=82]
+5 = 78

 



 
74 W
Tungsten
AR = 141
0 = 130
+4 = 80: [CN6=80]
+5 = 76
+6 = 74



 

 

75 Re
Rhenium
AR = 137
0 = 128
+4 = 77: [CN6=77]
+5 = 72
+6 = 69
+7 = 67




 

76 Os
Osmium
AR = 135
0 = 126
+4 = 77: [CN6=77]
+5 = 71.5
+6 = 69

 

 

 

77 Ir
Iridium
AR = 136
0 = 127
+3 = 82: [CN6=82]
+4 = 76.5: [CN6=77]
+5 = 71


 

 

78 Pt
Platinum
AR = 139
0 = 130
+2 = 94: [SQ:CN4=74; CN6=94]
+4 = 76.5
: [CN6=77]
+5 = 71



 
79 Au
Gold
AR = 146
0 = 134
+1 = 51: [CN6=151]
+3 = 99: [SQ:CN4=82; CN6=99]
+5 = 71



 
80 Hg
Mercury
AR = 157
0 = 149
+1 = 133
+2 = 116: [CN2=83; CN4=110; CN6=116; CN8=128]


 


 

81 Tl
Thallium
AR = 171
0 = 148
+1 = 147
+3 = 95: [CN4=89; CN6=103; CN8=112]


 



 

82 Pb
Lead
AR = 175
0 = 147
+2 = 120: [CN4=112; CN6=133; CN8=143; CN10=154; CN12=163]
+4 = 84:
[CN4=79; CN6=92; CN8=108]
83 Bi
Bismuth
AR = 170
0 = 146
+3 = 96: [CN6=117; CN8=131]
+5 = 74


 




84 Po
Polonium
AR = 176
0 = 146
+4: [CN6=108; CN8=122]
+6 = 67







85 At
Astatine
AR = 127
0 = 145
+7 = 62: [CN6=76]


 

 

 


86 Rn
Radon
AR = 120




 


 


 

 
87 Fr
Francium
+1 = 180: [CN6=194]


88 Ra
Radium
+2 = 143: [CN8=162; CN12=184]
[89-102]
Actinoid
103 Lr
Lawrencium




104 Rf





105 Db





106 Sg





107 Bh





108 Hs





109 Mt





110 Ds





111 Uuu





112 Uub





  114 Uuq




 
{lanthanides} {57-70} 57 La
Lanthanum
AR = 187
0 = 169
+3 = 117.2: [CN6=117; CN8=130; CN10=141; CN12=150]
 

58 Ce
Cerium
AR = 181
0 = 165
+3 = 103: [CN6=115;
CN8=128;
CN10=139;
CN12=148]
+4 = 92

59 Pr
Praseodymium
AR = 182
0 = 165
+3 = 101: [CN6= 113; CN8=127]
+4 = 90

 

60 Nd
Neodymium
AR = 182
0 = 184
+3 = 100: [CN6=112; CN8=125; CN12=141]

 

61 Pm
Prometium
AR = 205
0 = 163
+3 = 97: [CN6=111; CN8=123]


 

62 Sm
Samarium
AR = 181
0 = 162
+3 = 96: [CN6=110; CN8=122; CN12=138]

 

63 Eu
Europium
AR = 199
0 = 185
+2 = 95
+3 = 120.6: [CN6=109; CN8=121]

 

64 Gd
Gadolinium
AR = 179
0 = 161
+3 = 94: [CN6=108; CN8=119]

 


65 Tb
Terbium
AR = 180
0 = 159
+3 = 92: [CN6=106; CN8=118]
+4 = 84

 

66 Dy
Dysprosium
AR = 180
0 = 159
+3 = 91: [CN6=105; CN8=117]


 

67 Ho
Holmium
AR = 179
0 = 158
+3 = 90: [CN6=104; CN8=116; CN10=126]



68 Er
Erbium
AR = 178
0 = 157
+3 = 89: [CN6=103; CN8=114]


 

69 Th
Thulium
AR = 177
0 = 156
+3 = 87: [CN6=102; CN8=113]


 

70 Yb
Ytterbium
AR = 194
+2 = 93
+3 = 112: [CN6=101; CN8=113]


 
 
 
{actinides} [89-102] 89 Ac
Actinium
AR = 188
+3 = 118: [CN6=126]

 
 
 
90 Th
Thorium
AR = 180
0 = 165
+4 = 102: [CN6=108; CN8=119; CN10=127; CN12=135]
91 Pa
Protactinium
AR = 161
+3 = 113
+5 = 89

 
 
 

92 U
Uranium
AR = 138
0 = 142
+4 = 97
+6 = 80

 
 

93 Np
Neptunium
AR = 130
+3 = 110
+4 = 95

 



94 Pu
Plutonium
AR = 151
+3 = 108
+4 = 93


 


95 Am
Americium
AR = 173
+3 = 107
+4 = 92


 


96 Cm
Curium
AR = 299


 

 


97 Bk
Berkelium
AR = 297


 

 


98 Cf
Californium
AR = 295


 

 


99 Es
Einsteinium
AR = 292


 

 


100 Fm
Fermium
AR = 290


 

 


101 Md
Mendelevium
AR = 287


 

 


102 No
Nobelium
AR = 285


 

 


 

        * The common ionic states are in green.

The size of an atom or ion depends on the size of the nucleus as well as the number of electrons. In general, atoms with more electrons have larger radii than those with fewer electrons.

The magnitude of ionic radii in the ionic crystals is mainly influenced by the following factors:
        i) Coordination number.
        The coordination number is defined as the number of atoms that surround a particular atom or ion in the structure. With the increase of coordination number, the inter-ionic distance and thus the ionic radius increase because each ion with a greater coordination number is surrounded by a greater number of ions and thus results in less attraction between the ions.
        ii) Radius ratio.
        Radius ratio influences the magnitude of ionic radii.
        iii) Covalent character.
        Covalent character in the ionic bond existing between the cation and anion decreases the inter-ionic distance, resulting in a smaller ionic radius.

Other factors that influence the ionic radii are:
        iv) Ionic radii increase for a given coordination number with increasing Z within a periodic group.
        v) Ionic radii decrease with increasing nuclear charge for isoelectronic ions.
        vi) Ionic radii decrease with increase of ionic charge for the same Z. Therefore, as the charge on the ions becomes more positive, there will be fewer electrons and the ions will have smaller radii. On the other hand, as the charge on the ions becomes more negative, there will be more electrons and the ions will have larger radii (see Table 3131).
        vii) Larger ionic radius for high-spin ions than for low-spin ions of the same species and charge.
        viii) As the atomic number increases in any given column of the Periodic Table, the numbers of protons and electrons increase and thus the size of the atom or ion increases.
        ix) The ionic radii decrease with increase in atomic number as indicated in Figure 3131.

Ionic radii of 3d elements

Figure 3131. Ionic radii of 3d elements.

 

 

 

 

 

 

 

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