Periodic table

The periodic table is a table that puts all known chemical elements in a specific order. Elements that have similar characteristics are often put near each other. In the table, the elements are placed in the order of their atomic numbers starting with the lowest number of one, hydrogen. The atomic number of an element is the same as the number of protons in that particular nucleus of an atom. In the periodic table the elements are arranged into periods and groups. A row of elements across the table is called a period. Each period has a number; from 1 to 8. Period 1 has only 2 elements in it: hydrogen and helium. Period 2 and Period 3 both have 8 elements. Other periods are longer. Elements in a period have consecutive atomic numbers.

Periodic_table_large
A standard periodic table

A column of elements down the table is called a group. There are 18 groups in the standard periodic table. Each group has a number: from 1 to 18. Elements in a group have electrons arranged in similar ways, according to the number of valency electrons, which gives them similar chemical properties (they behave in similar ways). For example, group 18 is known as the noble gases because they are all gases and they do not combine with other atoms.

There are two systems of group numbers; one using Arabic numerals (1,2,3) and the other using Roman numerals (I, II, III). The Roman numeral names were used in most of the 20th century. In 1990 the International Union of Pure and Applied Chemistry (IUPAC) decided to use the new system with Arabic numerals, to replace the two old group systems that used Roman numerals.

The periodic table has been used by chemists to observe patterns and relationships between elements. There are 3 main groups in the Periodic Table; metals, metalloids, and nonmetals. For example, elements to the bottom and far left of the table are the most metallic, and elements on the top right are the least metallic. (e.g. caesium is much more metallic than helium). There are also many other patterns and relationships.

The periodic table was invented by the Russian chemist Dmitry Ivanovich Mendeleyev (1834–1907). In his honor, element 101 was named after him, mendelevium.

Standard periodic table

Group → 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Period ↓
1 1
H

Hydrogen


2
He

Helium

2 3
Li

Lithium

4
Be

Beryllium


5
B

Boron

6
C

Carbon

7
N

Nitrogen

8
O

Oxygen

9
F

Fluorine

10
Ne

Neon

3 11
Na

Sodium

12
Mg

Magnesium


13
Al

Aluminium

14
Si

Silicon

15
P

Phosphorus

16
S

Sulfur

17
Cl

Chlorine

18
Ar
4 19
KPotassium
20
Ca

Calcium

21
Sc

Scandium

22
Ti

Titanium

23
V

Vanadium

24
Cr

Chromium

25
Mn

Manganese

26
Fe

Iron

27
Co

Cobalt

28
Ni

Nickel

29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
5 37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
6 55
Cs
56
Ba
*

Lanthanides

72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
7 87
 Fr
88
Ra
**

Actinides

104
Rf
105
Db
106
Sg
107
Bh
108
Hs
109
Mt
110
Ds
111
Rg
112
Cn
113
Nh
114
Fl
115
Mc
116
Lv
117
Ts
118
Og
8 119
 Uue
120
Ubn

* Lanthanide Series 57
La
58
Ce
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
** Actinide Series 89
Ac
90
Th
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cf
99
Es
100
Fm
101
Md
102
No
103
Lr
Chemical Series of the Periodic Table
State at standard temperature and pressure. The colour of the number (atomic number) above the element symbol shows the state of the element at normal conditions.
  • those in blue are gases
  • those in green are liquids
  • those in black are solid
Radioactivity
  • Those with solid borders have stable isotopes (Primordial elements)
  • Those with dashed borders have only radioactive naturally occurring isotopes
  • Those with dotted borders do not occur naturally (Synthetic Elements)
  • Those without borders are too radioactive to have been discovered yet.

Other arrangements of the Periodic Table

The version of the periodic table shown above is the one most used. Other widespread versions are shown below:

Other versions

Periodic Table Media

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