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 | change source]

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

Argon

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

Copper

30
Zn

Zinc

31
Ga

Gallium

32
Ge

Germanium

33
As

Arsenic

34
Se

Selenium

35
Br

Bromine

36
Kr

Krypton

5

37
Rb

Rubidium

38
Sr

Strontium

39
Y

Yttrium

40
Zr

Zirconium

41
Nb

Niobium

42
Mo

Molybdenum

43
Tc

Technetium

44
Ru

Ruthenium

45
Rh

Rhodium

46
Pd

Palladium

47
Ag

Silver

48
Cd

Cadmium

49
In

Indium

50
Sn

Tin

51
Sb

Antimony

52
Te

Tellurium

53
I

Iodine

54
Xe

Xenon

6

55
Cs

Cesium

56
Ba

Barium

*

Lanthanides

72
Hf

Halfnium

73
Ta

Tantalum

74
W

Tungsten

75
Re

Rhenium

76
Os

Osmium

77
Ir

Iridium

78
Pt

Platinum

79
Au

Gold

80
Hg

Mercury

81
Tl

Thallium

82
Pb

Lead

83
Bi

Bismuth

84
Po

Polonium

85
At

Astatine

86
Rn

Radon

7

87
Fr

Francium

88
Ra

Radium

**

Actinides

104
Rf

Rutherfordium

105
Db

Dubnium

106
Sg

Seaborgium

107
Bh

Bohrium

108
Hs

Hassium

109
Mt

Meitnerium

110
Ds

Darmstadtium

111
Rg

Roentgenium

112
Cn

Copernicium

113
Nh

Nihonium

114
Fl

Flerovium

115
Mc

Moscovium

116
Lv

Livermorium

117
Ts

Tennesine

118
Og

Oganesson

8

119
Uue

Ununennium

120
Ubn

Unbinilium

* Lanthanide Series

57
La

Lanthanum

58
Ce

Cerium

59
Pr

Praseodymium

60
Nd

Neodymium

61
Pm

Promethium

62
Sm

Samarium

63
Eu

Europium

64
Gd

Gadolinium

65
Tb

Terbium

66
Dy

Dysprosium

67
Ho

Holmium

68
Er

Erbium

69
Tm

Thulium

70
Yb

Ytterbium

71
Lu

Lutetium

** Actinide Series

89
Ac

Actinium

90
Th

Thorium

91
Pa

Protactinium

92
U

Uranium

93
Np

Neptunium

94
Pu

Plutonium

95
Am

Americium

96
Cm

Curium

97
Bk

Berkelium

98
Cf

Californium

99
Es

Einsteinium

100
Fm

Fermium

101
Md

Mendeleevium

102
No

Nobelium

103
Lr

Lawrencium

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 | change source]

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.