3.1 The Periodic Table – classifying the elements
stepped line in Figure 3.2. One of the first uses of the Periodic Table now becomes clear. Although we may never have seen a sample of the element hafnium (Hf), we know from a glance at the table that it is a metal. We may also be able to predict some of its properties.
All modern versions of the Periodic Table are based on the one put forward by Mendeleev. An example is given in Figure 3.2.
Metals and non-metals
In the Periodic Table: ◆ the elements are arranged in order of increasing proton number (atomic number) ◆ the vertical columns of elements with similar properties are called groups ◆ the horizontal rows are called periods.
b
= atomic number
1
Period 1
4
H
He
Hydrogen
Helium
1
Period 2 Period 3 Period 4 Period 5 Period 6 Period 7
7
9
11
12
14
16
19
2 20
Li
Be
B
C
N
O
F
Ne
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
3 23
4 24
5 27
6 28
7 31
8 32
9 35.5
10 40
Na
Mg
Al
Si
P
S
Cl
Ar
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulfur
Chlorine
Argon
11 39
12 40
45
48
51
52
55
56
59
59
64
65
13 70
14 73
15 75
16 79
17 80
18 84
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Potassium
Calcium
Scandium
Titanium
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Gallium
Germanium
Arsenic
Selenium
Bromine
Krypton
19 86
20 88
21 89
22 91
23 93
24 96
25 –
26 101
27 103
28 106
29 108
30 112
31 115
32 119
33 122
34 128
35 127
36 131
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Rubidium
Strontium
Yttrium
Zirconium
Niobium
Molybdenum
Technetium
Ruthenium
Rhodium
Palladium
Silver
Cadmium
Indium
Tin
Antimony
Tellurium
Iodine
Xenon
37 133
38 137
39
40 178
41 181
42 184
43 186
44 190
45 192
46 195
47 197
48 201
49 204
50 207
51 209
52 –
53 –
54 –
Cs
Ba
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
Caesium
Barium
Hafnium
Tantalum
Tungsten
Rhenium
Osmium
Iridium
Platinum
Gold
Mercury
Thallium
Lead
Bismuth
Polonium
Astatine
Radon
55 –
56 –
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Fr
Ra
Francium
Radium
87
88
La to Lu Ac to Lr 139
140
141
144
–
150
152
157
159
163
165
167
169
173
175
La
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Lanthanum
Cerium
Praseodymium
Neodymium
Promethium
Samarium
Europium
Gadolinium
Terbium
Dysprosium
Holmium
Erbium
Thulium
Ytterbium
Lutetium
57 –
58 –
59 –
60 –
61 –
62 –
63 –
64 –
65 –
66 –
67 –
68 –
69 –
70 –
71 –
Ac
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
Actinium
Thorium
Protactinium
Uranium
Neptunium
Plutonium
Americium
Curium
Berkelium
Californium
Einsteinium
Fermium
Mendelevium
Nobelium
Lawrencium
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
Elements in Groups I to 0 are sometimes known as the main-group elements.
Figure 3.2
56
Group 0
b
Group VII
Name
Group VI
a = relative atomic mass X = symbol
a
X
Group V
Group II
Group I
Key:
Group III
The main distinction in the table is between metals and non-metals. Metals are clearly separated from non-metals. The non-metals are grouped into the top right-hand region of the table, above the thick
Group IV
There are 94 naturally occurring elements. Some are very rare. Francium, for instance, has never been seen. The radioactive metals neptunium and plutonium, which we make artifically in quite large amounts, occur only in very small (trace) quantities naturally. Most of the elements (70) can be classified as metals. Together they form a group of elements whose structures are held together by a particular type of bonding between the atoms. The metals have a number of physical properties that are broadly the same for all of them (Table 3.1).
The reactive metals: Group I – the alkali metals; Group II – the alkaline earth metals
The ‘poor’ metals
The non-metals: includes Group VII – the halogens
The transition elements: hard, strong and dense metals
The metalloids: includes semiconductors, e.g. silicon and germanium
The noble gases: very unreactive
The Periodic Table, showing the major regions. (Except for chlorine, the relative atomic masses are given to the nearest whole number.)
Cambridge IGCSE Chemistry
Original material © Cambridge University Press 2014