Basics ‹ 53
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. Metalloids have 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. Nonmetals
have 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 electrons 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). Periods are the horizontal rows, which have consecutive atomic num-
bers. 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 groups or 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.117
Ts
[294]118
Og
[294]113
Nh
[284.18]114
FI
[289.19]115
Mc
[288.19]116
Lv
[293]345678910 11 12 13 14 15 16 17Key:
Atomic number
Symbol
Atomic weight (mean relative mass)57–70
*
89 –102
**1
1
1.008H
3
Li6.94
11
Na
22.98976928(2)
19
39.0983(1)K
37
Rb
85.4678(3)
55
132.9054519(2)Cs
87
Fr
[223.02]
24
9.012182(3)Be
12
Mg
24.3050(6)
20
40.078(4)Ca
38
Sr
87.62(1)
56
137.327(7)Ba
88
Ra
[226.03]9
18.9984032(5)F
17
Cl
35.45
35
79.904(1)Br
53
I
126.90447(3)
85
At[210]18
2
4.002602(2)He
10
20.1797(6)Ne
18
Ar
39.948(1)
36
83.798(2)Kr
54
Xe
131.293(6)
86
Rn[222]*lanthanoids**actinoids21
44.955912(6)Sc
39
Y
88.90585(2)
71
174.9668(1)Lu
103
Lr
[262.11]57
La
138.90547(7)
89
[227.03]Ac22
47.867(1)Ti
40
Zr
91.224(2)
72
178.49(2)Hf
104
Rf
[265.12]58
Ce
140.116(1)
90
232.03806(2)Th23
50.9415(1)V
41
Nb
92.90638(2)
73
180.94788(2)Ta
105
Db
[268.13]59
Pr
140.90765(2)
91
231.03588(2)Pa24
51.9961(6)Cr
42
Mo
95.96(2)
74
183.84(1)W
106
Sg
[271.13]60
Nd
144.242(3)
92
238.02891(3)U25
54.938045(5)Mn
43
Tc
[97.91]
75
186.207(1)Re
107
Bh
[270]61
Pm
[144.91]
93
[237.05]Np26
55.845(2)Fe
44
Ru
101.07(2)
76
190.23(3)Os
108
Hs
[277.15]62
Sm
150.36(2)
94
[244.06]Pu27
58.933195(5)Co
45
Rh
102.90550(2)
77
192.217(3)Ir
109
Mt
[276.15]63
Eu
151.964(1)
95
Am[243.06]28
58.6934(4)Ni
46
Pd
106.42(1)
78
195.084(9)Pt
110
Ds
[281.16]64
Gd
157.25(3)
96
Cm[247.07]29
63.546(3)Cu
47
Ag
107.8682(2)
79
196.966569(4)Au
111
Rg
[280.16]65
Tb
158.92535(2)
97
[247.07]Bk30
65.38(2)Zn
48
Cd
112.411(8)
80
200.59(2)Hg
112
Cn
[285.17]66
Dy
162.500(1)
98
[251.08]Cf5
10.81B
13
Al
26.9815386(2)
31
69.723(1)Ga
49
In
114.818(3)
81
204.38Tl67
Ho
164.93032(2)
99
[252.08]Es6
12.011C
14
Si
28.085
32
72.63(1)Ge
50
Sn
118.710(7)
82
207.2(1)Pb68
Er
167.259(3)
100
Fm[257.10]7
14.007N
15
P
30.973762(2)
33
74.92160(2)As
51
Sb
121.760(1)
83
208.98040(1)Bi69
Tm
168.93421(2)
101
Md[258.10]8
15.999O
16
S
32.06
34
78.96(3)Se
52
Te
127.60(3)
84
Po[209]70
Yb
173.054(5)
102
[259.10]NoThe periodic tableFigure 5.4 The periodic table.