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Periodic Table of the Elements

Author: Robert Husted, Mollie Boorman

The periodic table of the chemical elements is a tabular method of displaying the chemical elements, first devised in 1869 by the Russian chemist Dmitri Mendeleev. Mendeleev intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as many new elements have been discovered, and new theoretical models have been developed to explain chemical behaviour.

  1A   8A
1 1
H

1.008
2A 3A 4A 5A 6A 7A 2
He
4.003
2 3
Li
6.941
4
Be

9.012
5
B
10.81
6
C
12.01
7
N
14.01
8
O
16.00
9
F
19.00
10
Ne
20.18
3 11
Na

22.99
12
Mg

24.31
3B 4B 5B 6B 7B ------ 8B ------ 1B 2B 13
Al
26.98
14
Si
28.09
15
P
30.97
16
S
32.07
17
Cl
35.45
18
Ar
39.95
4 19
K
39.10
20
Ca
40.08
21
Sc
44.96
22
Ti
47.88
23
V
50.94

24
Cr
52.00

25
Mn
54.94

26
Fe
55.85
27
Co
58.47
28
Ni
58.69
29
Cu
63.55
30
Zn
65.39
31
Ga
69.72
32
Ge
72.59
33
As
74.92
34
Se
78.96
35
Br
79.90
36
Kr
83.80
5 37
Rb
85.47
38
Sr
87.62
39
Y
88.91
40
Zr
91.22
41
Nb
92.91
42
Mo
95.94
43
Tc
(98)
44
Ru
101.1
45
Rh
102.9
46
Pd
106.4
47
Ag
107.9
48
Cd
112.4
49
In
114.8
50
Sn
118.7
51
Sb
121.8
52
Te
127.6
53
I
126.9
54
Xe
131.3
6 55
Cs
132.9
56
Ba
137.3
57
La1)
138.9
72
Hf
178.5
73
Ta
180.9
74
W
183.9
75
Re
186.2
76
Os
190.2
77
Ir
190.2
78
Pt
195.1
79
Au
197.0
80
Hg
200.5
81
Tl
204.4
82
Pb
207.2
83
Bi
209.0
84
Po
(210)
85
At
(210)
86
Rn
(222)
7 87
Fr
(223)
88
Ra
(226)
89
Ac2)
(227)
104
Rf
(257)
105
Db
(260)
106
Sg
(263)
107
Bh
(262)
108
Hs
(265)
109
Mt
(266)
110
Ds
(269)
111
Rg
(269)
112
Cn
(277)
 

1) Lanthanides 58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(147)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm 168.9
70
Yb
173.0
71
Lu
175.0
2) Actinides 90
Th
232.0
91
Pa
(231)
92
U
(238)
93
Np
(237)
94
Pu
(242)
95
Am
(243)
96
Cm
(247)
97
Bk
(247)
98
Cf
(249)
99
Es
(254)
100
Fm
(253)
101
Md
(256)
102
No
(254)
103
Lr
(257)

Groups

A group, also known as a family, is a vertical column in the periodic table of the elements. Groups are considered the most important way of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group these groups tend to be given trivial (non-scientific) names, e.g. the alkali metals, halogens and noble gases. Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Groups 14 and 15). Modern quantum mechanical theories of atomic structure explain that elements within the same group have the same electron configurations in their valence shell, which is the largest factor in accounting for their similar chemical properties.

Periods

A period is a horizontal row in the periodic table of the elements. Although groups are the most common way of classifying elements, there are some regions of the period table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the d-block (or "transition metals"), and especially for the f-block, where the lanthanoids and actinoids form two substantial horizontal series of elements.



Last Update: 2011-02-16