periodicity of elements ionic radii and covalent radii.

1. Periodicity of Elements:Covalent and
ionic radius
Dr. Mithil Fal Desai
Shree Mallikarjun and Shri Chetan
Manju Desai College Canacona Goa

2. Covalent radius
Covalent radius is the half the inter-nuclear distance
between two atoms that are covalently bonded.
e-
e-
2r
X atom X atom

3. Periodic trend in Covalent radii
H
30
He
Li
123
Be
89
B
90
C
77
N
75
O
73
F
71
Ne
Na
157
Mg
136
Al
130
Si
118
P
110
S
102
Cl
99
Ar
K
203
Ca
174
Sc
144
Ti
122
V
122
Cr
117
Mn
117
Fe
117
Co
116
Ni
115
Cu
117
Zn
125
Ga
125
Ge
122
As
121
Se
114
Br
114
Kr
200
Rb
216
Sr
191
Y
162
Zr
135
Nb
134
Mo
129
Tc
-
Ru
124
Rh
125
Pd
128
Ag
134
Cd
141
In
150
Sn
140
Sb
141
Te
137
I
133
Xe
220
Cs
235
Ba
198
La
169
Hf
144
Ta
134
W
130
Re
128
Os
126
Ir
126
Pt
129
Au
134
Hg
144
Tl
155
Pb
146
Bi
152
Po At Rn
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg
Ce
165
Pr
164
Nd
164
Pm
-
Sm
166
Eu
185
Gd
161
Tb
159
Dy
159
Ho
158
Er
157
Tm
156
Yb
170
Lu
156
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Radius values in pm
Increases
Decreases

4. Ionic radius
Ionic radius of element is related to the distance
between centres of neighboring atoms (cation
and anion) which share an ionic bond.
e-
e-
e-
e- e-
e-
e-
e-
r + R
X YX+ Y-

5. Periodic trend in ionic radii
(+1) (+2)
H
(-2) (-1)
He
Li
90
Be
59
B C N
O
126
F
119
Ne
Na
116
Mg
86
Al Si P
S
170
Cl
167
Ar
K
152
Ca
114
Sc
88
Ti
74
V Cr
Mn Fe Co Ni Cu
91
Zn
88
Ga
76
Ge As
Se
184
Br
182
Kr
Rb
166
Sr
132
Y Zr Nb Mo Tc Ru Rh Pd
Ag
108
Cd
190
In
94
Sn Sb
Te
207
I
206
Xe
Cs
181
Ba
149
La
117
Hf Ta W Re Os Ir Pt
Au
151
Hg
116
Tl
102
Pb Bi Po At Rn
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
Lu
100
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Radius values in pm
Increases
Decreases

6. Ionic radii (continue)
• Na (186 pm) and Na+ (102 pm)
• Fe( 117pm); Fe+2(78.0 pm) and Fe+3(64.5 pm)
• Cl(99 pm) and Cl- (184pm)
• Ba+2 149 pm and 156 pm for coordination
number 6 and 8, respectively

7. Points to remember
• Covalent radius and ionic radius
Decreases in along the row as atomic number
increases.
Increases down the group as atomic number
increases.
• The ionic radius of cation is smaller than covalent
radius.
• The ionic radius of anion is bigger than covalent radius.
• The coordination number affects the ionic radius of the
atom.