Chemistry Reference
In-Depth Information
Increase
1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
Rf
105
Db
106
Sg
107
Bh
108
Hs
109
Mt
110
Ds
111
Rg
112
Cn
FIGURE 2.7
General trend of the increase of atomic radii in the periodic table.
TABLE 2.9
The Lanthanide Contraction
Element and
Atomic Number
Å
Xe
58
Ce
1.85
4f
1
5d
1
6s
2
59
Pr
2.47
4f
3
6s
2
60
Nd
2.06
4f
4
6s
2
61
Pm
2.05
4f
5
6s
2
62
Sm
2.38
4f
6
6s
2
63
Eu
2.31
4f
7
6s
2
64
Gd
2.33
4f
7
5d
1
6s
2
65
Tb
2.25
4f
9
6s
2
66
Dy
2.28
4f
10
6s
2
67
Ho
2.26
4f
11
6s
2
68
Er
2.26
4f
12
6s
2
69
Tm
2.22
4f
13
6s
2
70
Yb
2.22
4f
14
6s
2
71
Lu
2.17
4f
14
5d
1
6s
2
more strongly attracted by the nucleus, leading to smaller atomic radii than expected.
Moreover they have very similar, and in some cases nearly identical, sizes. This effect
in the two series is known as the
lanthanide contraction
or
actinide contraction
.
Similarly, the contractions that occur in the 4th period, in elements that have the
d orbital completely filled (d
10
), occur as a result of poor shielding of the electrons in
the d orbital. This contraction is much less pronounced compared to the lanthanides.
The elements that show this effect are Ga, Ge, As, Se, and Br.
However, the size of the atoms can only be assessed approximately depend-
ing upon the bonds that form between two adjacent atoms. Several measures are
described: the metallic radius, the covalent radius, and the ionic radius. The most
straightforward, the metallic radius, is equal to half of the distance between two
adjacent atoms in the metallic network.
