Atomic Numbers Table

Atomic Numbers

The elements on the modern periodic table are listed in order of increasing atomic number. The number of protons in the nucleus of an atom is its atomic number. The number of protons tells us what an element is (i.e., an element with 6 protons is a carbon atom, no matter how many neutrons may be present). The number of protons determines how many electrons are around the nucleus, and how these electrons are arranged determines most of an element’s chemical behaviour.

1A 2A 3A 4A 5A 6A 7A 8A
(1) (2) (13) (14) (15) (16) (17) (18)
3B 4B 5B 6B 7B 8B 1B 2B
(3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
1 1 2
2 3 4 5 6 7 8 9 10
3 11 12 13 14 15 16 17 18
4 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
5 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
6 55 56 57   72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
7 87 88 89   104 105 106 107 108 109 110 111 112 114
6   58 59 60 61 62 63 64 65 66 67 68 69 70 71
7   90 91 92 93 94 95 96 97 98 99 100 101 102 103

In an atomic number-based periodic table, elements with similar chemical properties tend to fall into the same column (group). For example, all of the elements in Group 1A are soft metals that react violently with water and make 1+ charges. All of the elements in Group 8A are nonreactive monatomic gases at room temperature. In other words, the properties of chemical elements tend to repeat themselves over and over again as their mass goes up.

In Dimitri Mendeleev’s first periodic table, published in 1869, the elements were arranged in order of increasing atomic mass. At the time, the nucleus had not yet been found, and no one knew how the inside of an atom was put together, so atomic mass was the only way to organise the elements. Once the structure of the nucleus was understood, it was clear that the atomic number was what controlled the properties of the elements.

Atomic Number Symbol Name Atomic Mass (amu, g/mol)
1 H Hydrogen 1.00797
2 He Helium 4.00260
3 Li Lithium 6.941
4 Be Beryllium 9.01218
5 B Boron 10.81
6 C Carbon 12.011
7 N Nitrogen 14.0067
8 O Oxygen 15.9994
9 F Fluorine 18.998403
10 Ne Neon 20.179
11 Na Sodium 22.98977
12 Mg Magnesium 24.305
13 Al Aluminum 26.98154
14 Si Silicon 28.0855
15 P Phosphorus 30.97376
16 S Sulfur 32.06
17 Cl Chlorine 35.453
18 Ar Argon 39.948
19 K Potassium 39.0983
20 Ca Calcium 40.08
21 Sc Scandium 44.9559
22 Ti Titanium 47.90
23 V Vanadium 50.9415
24 Cr Chromium 51.996
25 Mn Manganese 54.9380
26 Fe Iron 55.847
27 Co Cobalt 58.9332
28 Ni Nickel 58.70
29 Cu Copper 63.546
30 Zn Zinc 65.38
31 Ga Gallium 69.72
32 Ge Germanium 72.59
33 As Arsenic 74.9216
34 Se Selenium 78.96
35 Br Bromine 79.904
36 Kr Krypton 83.80
37 Rb Rubidium 85.4678
38 Sr Strontium 87.62
39 Y Yttrium 88.9059
40 Zr Zirconium 91.22
41 Nb Niobium 92.9064
42 Mo Molybdenum 95.94
43 Tc Technetium (98)
44 Ru Ruthenium 101.07
45 Rh Rhodium 102.9055
46 Pd Palladium 106.4
47 Ag Silver 107.868
48 Cd Cadmium 112.41
49 In Indium 114.82
50 Sn Tin 118.69
51 Sb Antimony 121.75
52 Te Tellurium 127.60
53 I Iodine 126.9045
54 Xe Xenon 131.30
55 Cs Cesium 132.9054
56 Ba Barium 137.33
57 La Lanthanum 138.9055
58 Ce Cerium 140.12
59 Pr Praseodymium 140.9077
60 Nd Neodymium 144.24
61 Pm Promethium (145)
62 Sm Samarium 150.4
63 Eu Europium 151.96
64 Gd Gadolinium 157.25
65 Tb Terbium 158.9254
66 Dy Dysprosium 162.50
67 Ho Holmium 164.9304
68 Er Erbium 167.26
69 Tm Thulium 168.9342
70 Yb Ytterbium 173.04
71 Lu Lutetium 174.967
72 Hf Hafnium 178.49
73 Ta Tantalum 180.9479
74 W Tungsten 183.85
75 Re Rhenium 186.207
76 Os Osmium 190.2
77 Ir Iridium 192.22
78 Pt Platinum 195.09
79 Au Gold 196.9665
80 Hg Mercury 200.59
81 Tl Thallium 204.37
82 Pb Lead 207.2
83 Bi Bismuth 208.9804
84 Po Polonium (209)
85 At Astatine (210)
86 Rn Radon (222)
87 Fr Francium (223)
88 Ra Radium 226.0254
89 Ac Actinium 227.0278
90 Th Thorium 232.0381
91 Pa Protactinium 231.0359
92 U Uranium 238.029
93 Np Neptunium 237.0482
94 Pu Plutonium (242)
95 Am Americium (243)
96 Cm Curium (247)
97 Bk Berkelium (247)
98 Cf Californium (251)
99 Es Einsteinium (252)
100 Fm Fermium (257)
101 Md Mendelevium (258)
102 No Nobelium (250)
103 Lr Lawrencium (260)
104 Rf Rutherfordium (261)
105 Db Dubnium (262)
106 Sg Seaborgium (263)
107 Bh Bohrium (262)
108 Hs Hassium (255)
109 Mt Meitnerium (256)
110 Ds Darmstadtium (269)
111 Rg Roentgenium (272)
112 Uub Ununbiium (277)
113 —— ———
114 Uuq Ununquadium  
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