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HOW DOES THE PERIODIC TABLE WORK?
The periodic table sets out the elements in a way that highlights similarities and
trends in their properties. Elements in the same group (column) have similar
properties. The properties change gradually along periods (rows) in the table –
elements on the left are metals, elements on the right are non-metals. As you
move across periods, the atomic number increases. Also, at the start of a period,
elements have one electron in their outer shell – by the end, they have eight.
The periodic table is a simple list of all the elements. The elements
are arranged by their atomic number. The information given for
each element includes atomic number, symbol, name, and mass
number. The vertical columns of the table are called groups, and
the horizontal rows are called periods.
WHAT IS AN ISOTOPE?
All elements have several forms called isotopes.
Each isotope of an element has the same atomic
number, but a different atomic mass. In carbon,
99 per cent of the atoms are isotope carbon 12,
and 1 per cent are carbon 13. Both isotopes have
six protons, but carbon 12 has six neutrons,
while carbon 13 has seven.
WHY IS THE PERIODIC TABLE USEFUL?
Scientists can tell a great deal about the
properties of an element, even before they do
experiments, by looking at its position in the
periodic table. They can decide whether it will be
a metal or a non-metal, judge how well it will
conduct electricity, and predict how it will react
with other elements.
WHY ARE ELEMENTS IN A GROUP SIMILAR?
The chemical properties of an element depend on the
number of electrons in its outer shell. Elements in the
same group have the same number of outer electrons.
For example, all the elements in Group 1 (alkali
metals) have one electron in their outer shells. They
are all silvery-white, highly reactive metals.
1 PERIODIC TABLE
Russian chemist Dimitri Ivanovich
Mendeleyev (1834–1907) drew up the
first periodaic table in 1869. Gaps in
Mendeleyev’s table suggested the existence
of elements that were not known at the
time. The missing elements have all since
been discovered – for example, scandium,
gallium, and germanium.
PERIODIC TABLE
The mass number gives the number
of protons and neutrons in the
nucleus. The mass numbers given on
this page are for the most common
isotope (form) of the element
The symbol is used as
shorthand for the element
in chemical equations
The atomic number
is the number of protons
in the nucleus
Alkali metals
Alkaline earth metals
Transition metals
Rare earths
Radioactive rare earths
Other metals
Semimetals
Non-metals
Noble gases
Hydrogen does
not belong to any
one group
Undefined
79
Au
Gold
197
KEY
1
H
Hydrogen
1
3
Li
Lithium
7
4
Be
Beryllium
9
11
Na
Sodium
23
12
Mg
Magnesium
24
19
K
Potassium
39
20
Ca
Calcium
40
37
Rb
Rubidium
85
38
Sr
Strontium
88
55
Cs
Caesium
133
56
Ba
Barium
138
87
Fr
Francium
223
88
Ra
Radium
226
57-71
89-103
21
Sc
Scandium
45
39
Y
Yttrium
89
22
Ti
Titanium
48
40
Zr
Zirconium
90
72
Hf
Hafnium
180
104
Rf
Rutherfordium
261
23
V
Vanadium
51
41
Nb
Niobium
93
73
Ta
Tantalum
181
105
Db
Dubnium
262
24
Cr
Chromium
52
42
Mo
Molybdenum
98
74
W
Tungsten
184
25
Mn
Manganese
55
43
Tc
Technetium
97
75
Re
Rhenium
187
107
Bh
Bohrium
264
26
Fe
Iron
56
44
Ru
Ruthenium
102
76
Os
Osmium
192
108
Hs
Hassium
267
27
Co
Cobalt
59
45
Rh
Rhodium
103
77
Ir
Iridium
193
109
Mt
Meitnerium
268
28
Ni
Nickel
58
46
Pd
Palladium
106
78
Pt
Platinum
195
29
Cu
Copper
63
47
Ag
Silver
107
79
Au
Gold
197
30
Zn
Zinc
64
48
Cd
Cadmium
11 4
80
Hg
Mercury
202
31
Ga
Gallium
69
49
In
Indium
11 5
81
Ti
Thallium
205
32
Ge
Germanium
74
50
Sn
Tin
120
82
Pb
Lead
208
33
As
Arsenic
75
51
Sb
Antimony
121
83
Bi
Bismuth
209
34
Se
Selenium
80
52
Te
Tellurium
130
84
Po
Polonium
209
35
Br
Bromine
79
53
I
Iodine
127
85
At
Astatine
210
36
Kr
Krypton
84
13
Al
Aluminium
27
14
Si
Silicon
28
15
P
Phosphorus
31
16
S
Sulphur
32
17
Cl
Chlorine
35
18
Ar
Argon
40
5
B
Boron
11
6
C
Carbon
12
7
N
Nitrogen
14
8
O
Oxygen
16
9
F
Fluorine
19
10
Ne
Neon
20
2
He
Helium
4
54
Xe
Xenon
132
86
Rn
Radon
222
89
Ac
Actinium
227
90
Th
Thorium
232
91
Pa
Protactinium
231
92
U
Uranium
238
93
Np
Neptunium
237
94
Pu
Plutonium
244
95
Am
Americium
243
96
Cm
Curium
247
97
Bk
Berkelium
247
98
Cf
Californium
251
99
Es
Einsteinium
254
100
Fm
Fermium
257
101
Md
Mendelevium
258
102
No
Nobelium
255
103
Lr
Lawrencium
256
57
La
Lanthanum
139
58
Ce
Cerium
140
59
Pr
Praseodymium
141
60
Nd
Neodymium
142
61
Pm
Promethium
145
62
Sm
Samarium
152
63
Eu
Europium
153
64
Gd
Gadolinium
158
65
Tb
Terbium
159
66
Dy
Dysprosium
164
67
Ho
Holmium
165
68
Er
Erbium
168
69
Tm
Thulium
169
70
Yb
Ytterbium
174
71
Lu
Lutetium
175
106
Sg
Seaborgium
268
110
Ds
Darmstadtium
281
111
Rg
Roentgenium
281
11 3
Uut
Ununtrium
284
11 4
Uuq
Ununquadium
289
11 5
Uup
Ununpentium
288
11 6
Uuh
Ununhexium
293
(117)
(Uus)
(Ununseptium)
(not known)
11 8
Uuo
Ununoctium
294
11 2
Cn
Copernicium
285