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.

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 change

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 color 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 change

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

Theodor Benfey arranged the elements in a spiral, around hydrogen. The atomic weight determines the position of the element.
Dmitry Ivanovich Mendeleyev used a flower arrangement; Actinides, Lanthanides are shown as loops beside the main group.
Timothy Stove arranged the elements by quantum number.
Betterman arranged the elements by their isoelectric properties, which can be converted to a polynomial form.
Triangular version, by Zmaczynski and Bayley
Arranged in a pyramid.