into thin sheets (malleable) and extruded into wires (ductile). Chemically, metals tend to
lose electrons in reactions, to form cations.
Elements bordering the stair-stepped line (B, Si, Ge, As, Sb, Te) are classified as metal-
loids. Metalloidshave properties of both metals and nonmetals. Their unusual electrical
properties make them valuable in the semiconductor and computer industry.
The rest of the elements, to the right of the metalloids, are called nonmetals.
Nonmetalshave properties that are often the opposite of metals. Some are gases, are poor
conductors of heat and electricity, are neither malleable nor ductile, and tend to gain elec-
trons in their chemical reactions to form anions.
Another way to group the elements on the periodic table is in terms of periods and
groups (families). Periodsare the horizontal rows, which have consecutive atomic numbers.
The periods are numbered from 1 to 7. Elements in the same period do not have similar
properties in terms of reactions.
The vertical rows on the periodic table are called groupsor families. They may be
labeled in one of two ways. An older and still widely used system is to label each group with
a Roman numeral and a letter, A or B. The groups that are labeled with an A are called the
main-group elements, while the B groups are called the transition elements. Two other
horizontal groups, the inner transition elements, have been pulled out of the main body
of the periodic table. The Roman numeral at the top of the main-group families indicates
the number of valence(outermost shell) electrons in that element. Valence electrons are
normally considered to be only the s and p electrons in the outermost energy level. The
transition elements (B groups) are filling d-orbitals, while the inner transition elements are
filling f-orbitals.
Basics 51
Periodic Table of the Elements
Periods
1 18
1
2 13 14 15 16 17
2
3
3 45 6 789 10 11 12
IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA 0
4
5
6
7
1
1.0080H
1
H
1.0080
Atomic number
Symbol
Atomic Mass
3
6.941Li
4
9.01218Be
11
Na
22.9898
2
4.00260He
10
20.179Ne
18
Ar
39.948
9
18.9984F
17
Cl
35.453
8
15.9994O
16
S
32.06
7
14.0067N
15
P
30.9738
6
12.011C
14
Si
28.086
5
10.81B
13
Al
26.9815
12
Mg
24.305
19
39.102K
20
40.08Ca
37
85.4678Rb
38
87.62Sr
55
132.9055Cs
56
137.34Ba
87
Fr
(223)
88
Ra
226.0254
21
44.9559Sc
22
47.90Ti
39
88.9059Y
40
91.22Zr
57
138.9055La
72
178.49Hf
89
Ac
(227)
104
Unq
(261)
23
50.9414V
24
51.996Cr
41
92.9064Nb
42
Mo95.94
73
180.9479Ta
74
183.85W
105
Unp
(262)
106
Unh
(263)
25
54.9380Mn
26
55.847Fe
43
98.9062Tc
44
101.07Ru
75
186.2Re
76
190.2Os
27
58.9332Co
28
58.71Ni
45
102.9055Rh
46
106.4Pd
77
192.22Ir
78
195.09Pt
29
63.546Cu
47
107.868Ag
79
196.9665Au
30
65.37Zn
48
112.40Cd
80
200.59Hg
31
69.72Ga
49
114.82In
81
204.37Tl
32
72.59Ge
50
118.69Sn
82
207.2Pb
33
74.9216As
51
121.75Sb
83
208.9806Bi
34
78.96Se
52
127.60Te
84
(210)Po
35
79.904Br
53
126.9045I
85
(210)At
58
Ce
140.12
59
Pr
140.9077
60
Nd
144.24
61
Pm
(145)
62
Sm
150.4
63
Eu
151.96
64
Gd
157.25
65
Tb
158.9254
66
Dy
162.50
67
Ho
164.9303
68
Er
167.26
69
Tm
168.9342
70
Yb
173.04
71
Lu
174.97
90
232.0381Th
91
231.0359Pa
92
238.029U
93
237.0482Np
94
(242)Pu
95
Am(243)
96
Cm(247)
97
(249)Bk
98
(251)Cf
99
(254)Es
100
(253)Fm
101
Md(256)
102
No(254)
103
(257)Lr
36
83.80Kr
54
131.30Xe
86
(222)Rn
Modern
group
numbers
Classical
group
numbers
*
†
*
†
Figure 5.4 The periodic table.