H
1
Key
Hover over an element to see more information here, or click/tap an element to see more details. Use the menu on the left to highlight properties of the periodic table.


He
2
Li
3
Be
4
B
5
C
6
N
7
O
8
F
9
Ne
10
Na
11
Mg
12
Al
13
Si
14
P
15
S
16
Cl
17
Ar
18
K
19
Ca
20
Sc
21
Ti
22
V
23
Cr
24
Mn
25
Fe
26
Co
27
Ni
28
Cu
29
Zn
30
Ga
31
Ge
32
As
33
Se
34
Br
35
Kr
36
Rb
37
Sr
38
Y
39
Zr
40
Nb
41
Mo
42
Tc
43
Ru
44
Rh
45
Pd
46
Ag
47
Cd
48
In
49
Sn
50
Sb
51
Te
52
I
53
Xe
54
Cs
55
Ba
56
La
57
Hf
72
Ta
73
W
74
Re
75
Os
76
Ir
77
Pt
78
Au
79
Hg
80
Tl
81
Pb
82
Bi
83
Po
84
At
85
Rn
86
Fr
87
Ra
88
Ac
89
Rf
104
Db
105
Sg
106
Bh
107
Hs
108
Mt
109
Ds
110
Rg
111
Cn
112
Nh
113
Fl
114
Mc
115
Lv
116
Ts
117
Og
118
Ce
58
Pr
59
Nd
60
Pm
61
Sm
62
Eu
63
Gd
64
Tb
65
Dy
66
Ho
67
Er
68
Tm
69
Yb
70
Lu
71
Th
90
Pa
91
U
92
Np
93
Pu
94
Am
95
Cm
96
Bk
97
Cf
98
Es
99
Fm
100
Md
101
No
102
Lr
103

Values from CRC Handbook of Chemistry and Physics, 100th Edition (Internet Version 2019), John R. Rumble, ed., CRC Press/Taylor & Francis, Boca Raton, FL.

Standard atomic weights are from Wieser, M. E., et al., Pure Appl. Chem. 85, 1047, 2013 plus changes made through 2018 by the International Union of Pure and Applied Chemistry (IUPAC) Commission on Isotopic Abundances and Atomic Weights.

Each atomic weight had previously been given as a single value with an uncertainty that took into account both the measurement uncertainty and the variation in isotopic abundance in samples of the element from different terrestrial sources. For a variety of reasons, this fails to give complete information on the natural variability in isotopic abundance of several elements. Therefore, beginning in 2009 the IUPAC recommendations expressed the atomic weights of several elements as intervals rather than single numbers plus uncertainties. The symbol for these intervals is [a, b], where a is the lower bound of values found in normal terrestrial materials and b the upper bound. For the other elements in the table, a single recommended atomic weight value is given; the number in parentheses following the value gives the uncertainty in the last digit.

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