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Periodic table


The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number (number of protons), electron configurations, and recurring chemical properties. This ordering shows periodic trends, such as elements with similar behaviour in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the left, and non-metals on the right.

The rows of the table are called periods; the columns are called groups. Six groups have names as well as numbers: for example, group 17 elements are the halogens; and group 18, the noble gases. The periodic table can be used to derive relationships between the properties of the elements, and predict the properties of new elements yet to be discovered or synthesized. The periodic table provides a useful framework for analyzing chemical behaviour, and is widely used in chemistry and other sciences.

The Russian chemist Dmitri Mendeleev published the first widely recognized periodic table in 1869. He developed his table to illustrate periodic trends in the properties of the then-known elements. Mendeleev also predicted some properties of then-unknown elements that would be expected to fill gaps in this table. Most of his predictions were proved correct when the elements in question were subsequently discovered. Mendeleev's periodic table has since been expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour.

All elements from atomic numbers 1 (hydrogen) to 118 (oganesson) have been discovered or synthesized, with the most recent additions (nihonium, moscovium, tennessine, and oganesson) being confirmed by the International Union of Pure and Applied Chemistry (IUPAC) on December 30, 2015 and officially named on November 28, 2016: they complete the first seven rows of the periodic table.[1][2] The first 94 elements exist naturally, although some are found only in trace amounts and were synthesized in laboratories before being found in nature.[n 1] Elements with atomic numbers from 95 to 118 have only been synthesized in laboratories or nuclear reactors.[3] Synthesis of elements having higher atomic numbers is being pursued. Numerous synthetic radionuclides of naturally occurring elements have also been produced in laboratories.

Periodic table
Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Alkali metals Alkaline earth metals Pnicto­gens Chal­co­gens Halo­gens Noble gases
Period
1
Hydro­gen
1
H
He­lium
2
He
2
Lith­ium
3
Li
Beryl­lium
4
Be
Boron
5
B
Carbon
6
C
Nitro­gen
7
N
Oxy­gen
8
O
Fluor­ine
9
F
Neon
10
Ne
3
So­dium
11
Na
Magne­sium
12
Mg
Alumin­ium
13
Al
Sili­con
14
Si
Phos­phorus
15
P
Sulfur
16
S
Chlor­ine
17
Cl
Argon
18
Ar
4
Potas­sium
19
K
Cal­cium
20
Ca
Scan­dium
21
Sc
Tita­nium
22
Ti
Vana­dium
23
V
Chrom­ium
24
Cr
Manga­nese
25
Mn
Iron
26
Fe
Cobalt
27
Co
Nickel
28
Ni
Copper
29
Cu
Zinc
30
Zn
Gallium
31
Ga
Germa­nium
32
Ge
Arsenic
33
As
Sele­nium
34
Se
Bromine
35
Br
Kryp­ton
36
Kr
5
Rubid­ium
37
Rb
Stront­ium
38
Sr
Yttrium
39
Y
Zirco­nium
40
Zr
Nio­bium
41
Nb
Molyb­denum
42
Mo
Tech­netium
43
Tc
Ruthe­nium
44
Ru
Rho­dium
45
Rh
Pallad­ium
46
Pd
Silver
47
Ag
Cad­mium
48
Cd
Indium
49
In
Tin
50
Sn
Anti­mony
51
Sb
Tellur­ium
52
Te
Iodine
53
 I 
Xenon
54
Xe
6
Cae­sium
55
Cs
Ba­rium
56
Ba
Lan­thanum
57
La
1 asterisk
Haf­nium
72
Hf
Tanta­lum
73
Ta
Tung­sten
74
W
Rhe­nium
75
Re
Os­mium
76
Os
Iridium
77
Ir
Plat­inum
78
Pt
Gold
79
Au
Mer­cury
80
Hg
Thallium
81
Tl
Lead
82
Pb
Bis­muth
83
Bi
Polo­nium
84
Po
Asta­tine
85
At
Radon
86
Rn
7
Fran­cium
87
Fr
Ra­dium
88
Ra
Actin­ium
89
Ac
1 asterisk
Ruther­fordium
104
Rf
Dub­nium
105
Db
Sea­borgium
106
Sg
Bohr­ium
107
Bh
Has­sium
108
Hs
Meit­nerium
109
Mt
Darm­stadtium
110
Ds
Roent­genium
111
Rg
Coper­nicium
112
Cn
Nihon­ium
113
Nh
Flerov­ium
114
Fl
Moscov­ium
115
Mc
Liver­morium
116
Lv
Tenness­ine
117
Ts
Oga­nesson
118
Og
1 asterisk
Cerium
58
Ce
Praseo­dymium
59
Pr
Neo­dymium
60
Nd
Prome­thium
61
Pm
Sama­rium
62
Sm
Europ­ium
63
Eu
Gadolin­ium
64
Gd
Ter­bium
65
Tb
Dyspro­sium
66
Dy
Hol­mium
67
Ho
Erbium
68
Er
Thulium
69
Tm
Ytter­bium
70
Yb
Lute­tium
71
Lu

1 asterisk
Thor­ium
90
Th
Protac­tinium
91
Pa
Ura­nium
92
U
Neptu­nium
93
Np
Pluto­nium
94
Pu
Ameri­cium
95
Am
Curium
96
Cm
Berkel­ium
97
Bk
Califor­nium
98
Cf
Einstei­nium
99
Es
Fer­mium
100
Fm
Mende­levium
101
Md
Nobel­ium
102
No
Lawren­cium
103
Lr

black=solid green=liquid red=gas gray=unknown Color of the atomic number shows state of matter (at 0 °C and 1 atm)
Primordial From decay Synthetic Border shows natural occurrence of the element
Background color shows subcategory in the metal–metalloid–nonmetal trend:
Metal Metalloid Nonmetal Unknown
chemical
properties
Alkali metal Alkaline earth metal Lan­thanide Actinide Transition metal Post-​transition metal Polyatomic nonmetal Diatomic nonmetal Noble gas
Each chemical element has a unique atomic number (Z) representing the number of protons in its nucleus.[n 2] Most elements have differing numbers of neutrons among different atoms, with these variants being referred to as isotopes. For example, carbon has three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. Elements with no stable isotopes have the atomic masses of their most stable isotopes, where such masses are shown, listed in parentheses.

In the standard periodic table, the elements are listed in order of increasing atomic number (the number of protons in the nucleus of an atom). A new row (period) is started when a new electron shell has its first electron. Columns (groups) are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. oxygen and selenium are in the same column because they both have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.

As of 2016, the periodic table has 118 confirmed elements, from element 1 (hydrogen) to 118 (oganesson). Elements 113, 115, 117 and 118 were officially confirmed by the International Union of Pure and Applied Chemistry (IUPAC) in December 2015. Their proposed names, nihonium (Nh), moscovium (Mc), tennessine (Ts) and oganesson (Og) respectively, were announced by the IUPAC in June 2016 and made official in November 2016.

The first 94 elements occur naturally; the remaining 24, americium to oganesson (95–118) occur only when synthesized in laboratories. Of the 94 naturally occurring elements, 83 are primordial and 11 occur only in decay chains of primordial elements.No element heavier than einsteinium (element 99) has ever been observed in macroscopic quantities in its pure form, nor has astatine (element 85); francium (element 87) has been only photographed in the form of light emitted from microscopic quantities (300,000 atoms).

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