# Periodic table (crystal structure)

For elements that are solid at standard temperature and pressure the table gives the crystalline structure of the most thermodynamically stable form(s) in those conditions. In all other cases the structure given is for the element at its melting point. Data is presented only for the first 112 elements (hydrogen through copernicium; it is not available for any further ones), and predictions are given for elements that have never been produced in bulk (astatine, francium, and elements 100–112).

## Table

Crystal structure of elements in the periodic table
1
H
HEX
2
He
HCP
3
Li
BCC
4
Be
HCP
5
B
RHO
6
C
HEX
7
N
HEX
8
O
SC
9
F
SC
10
Ne
FCC
11
Na
BCC
12
Mg
HCP
13
Al
FCC
14
Si
DC
15
P
ORTH
16
S
ORTH
17
Cl
ORTH
18
Ar
FCC
19
K
BCC
20
Ca
FCC
21
Sc
HCP
22
Ti
HCP
23
V
BCC
24
Cr
BCC
25
Mn
BCC
26
Fe
BCC
27
Co
HCP
28
Ni
FCC
29
Cu
FCC
30
Zn
HCP
31
Ga
ORTH
32
Ge
DC
33
As
RHO
34
Se
HEX
35
Br
ORTH
36
Kr
FCC
37
Rb
BCC
38
Sr
FCC
39
Y
HCP
40
Zr
HCP
41
Nb
BCC
42
Mo
BCC
43
Tc
HCP
44
Ru
HCP
45
Rh
FCC
46
Pd
FCC
47
Ag
FCC
48
Cd
HCP
49
In
TETR
50
Sn
TETR
51
Sb
RHO
52
Te
HEX
53
I
ORTH
54
Xe
FCC
55
Cs
BCC
56
Ba
BCC
72
Hf
HCP
73
Ta
BCC/TETR
74
W
BCC
75
Re
HCP
76
Os
HCP
77
Ir
FCC
78
Pt
FCC
79
Au
FCC
80
Hg
RHO
81
Tl
HCP
82
Pb
FCC
83
Bi
RHO
84
Po
SC/RHO
85
At
[FCC]
86
Rn
FCC
87
Fr
[BCC]
88
Ra
BCC
104
Rf
[HCP]
105
Db
[BCC]
106
Sg
[BCC]
107
Bh
[HCP]
108
Hs
[HCP]
109
Mt
[FCC]
110
Ds
[BCC]
111
Rg
[BCC]
112
Cn
[HCP]
113
Nh

114
Fl

115
Mc

116
Lv

117
Ts

118
Og

57
La
DHCP
58
Ce
DHCP/FCC
59
Pr
DHCP
60
Nd
DHCP
61
Pm
DHCP
62
Sm
RHO
63
Eu
BCC
64
Gd
HCP
65
Tb
HCP
66
Dy
HCP
67
Ho
HCP
68
Er
HCP
69
Tm
HCP
70
Yb
FCC
71
Lu
HCP
89
Ac
FCC
90
Th
FCC
91
Pa
TETR
92
U
ORTH
93
Np
ORTH
94
Pu
MON
95
Am
DHCP
96
Cm
DHCP
97
Bk
DHCP
98
Cf
DHCP
99
Es
FCC
100
Fm
[FCC]
101
Md
[FCC]
102
No
[FCC]
103
Lr
[HCP]
Legend:
…/… mixed structure
[…] predicted structure
FCC: face centered cubic (cubic close packed)
ORTH: orthorhombic
TETR: tetragonal
RHO: rhombohedral
HEX: hexagonal
SC: simple cubic
MON: monoclinic
unknown or uncertain

## Unusual structures

Element crystal system coordination number notes
Mn cubic distorted bcc – unit cell contains Mn atoms in 4 different environments.[1]
Zn hexagonal distorted from ideal hcp. 6 nearest neighbors in same plane- 6 in adjacent planes 14% farther away[1]
Ga orthorhombic each Ga atom has one nearest neighbour at 244 pm, 2 at 270 pm, 2 at 273 pm, 2 at 279 pm.[1] The structure is related to Iodine.
Cd hexagonal distorted from ideal hcp. 6 nearest neighbours in the same plane- 6 in adjacent planes 15% farther away[1]
In tetragonal slightly distorted fcc structure[1]
Sn tetragonal 4 neighbours at 302 pm; 2 at 318 pm; 4 at 377 pm; 8 at 441 pm [1] white tin form (thermodynamical stable above 286.4 K)
Sb rhombohedral puckered sheet; each Sb atom has 3 neighbours in the same sheet at 290.8pm; 3 in adjacent sheet at 335.5 pm.[1] grey metallic form.
Hg rhombohedral 6 nearest neighbours at 234 K and 1 atm (it is liquid at room temperature and thus has no crystal structure at ambient conditions!) this structure can be considered to be a distorted hcp lattice with the nearest neighbours in the same plane being approx 16% farther away [1]
Bi rhombohedral puckered sheet; each Bi atom has 3 neighbours in the same sheet at 307.2 pm; 3 in adjacent sheet at 352.9 pm.[1] Bi, Sb and grey As have the same space group in their crystal
Po cubic 6 nearest neighbours simple cubic lattice. The atoms in the unit cell are at the corner of a cube.
Sm trigonal 12 nearest neighbours complex hcp with 9 layer repeat, ABCBCACAB....[2]
Pa tetragonal body centred tetragonal unit cell, which can be considered to be a distorted bcc
U orthorhombic strongly distorted hcp structure. Each atom has four near neighbours, 2 at 275.4 pm, 2 at 285.4 pm. The next four at distances 326.3 pm and four more at 334.2 pm.[3]
Np orthorhombic highly distorted bcc structure. Lattice parameters: a=666.3 pm, b=472.3 pm, c=488.7 pm [4][5]
Pu monoclinic slightly distorted hexagonal structure. 16 atoms per unit cell. Lattice parameters: a= 618.3 pm, b=482.2 pm, c=1096.3 pm, β= 101.79 ° [6][7]

## Usual crystal structures

### Close packed metal structures

Many metals adopt close packed structures i.e. hexagonal close packed and face centred cubic structures (cubic close packed). A simple model for both of these is to assume that the metal atoms are spherical and are packed together in the most efficient way (close packing or closest packing). In closest packing every atom has 12 equidistant nearest neighbours, and therefore a coordination number of 12. If the close packed structures are considered as being built of layers of spheres then the difference between hexagonal close packing and face centred cubic is how each layer is positioned relative to others. Whilst there are many ways that can be envisaged for a regular buildup of layers:

• hexagonal close packing has alternate layers positioned directly above/below each other, A,B,A,B, ......... (also termed P63/mmc, Pearson symbol hP2, strukturbericht A3) .
• face centered cubic has every third layer directly above/below each other,A,B,C,A,B,C,.......(also termed cubic close packing, Fm3m, Pearson symbol cF4, strukturbericht A1) .
• double hexagonal close packing has layers directly above/below each other, A,B,A,C,A,B,A,C,.... of period length 4 like an alternative mixture of fcc and hcp packing (also termed P63/mmc, Pearson Symbol hP4, strukturbericht A3' ).[8]
• α-Sm packing has a period of 9 layers A,B,A,B,C,B,C,A,C,.... (R3m, Pearson Symbol hR3, strukturbericht C19).[9]

#### Hexagonal close packed

In the ideal hcp structure the unit cell axial ratio is ${\displaystyle \scriptstyle 2{\sqrt {\frac {2}{3}}}}$ ~ 1.633, However, there are deviations from this in some metals where the unit cell is distorted in one direction but the structure still retains the hcp space group—remarkable all the elements have a ratio of lattice parameters c/a < 1.633 (best are Mg and Co and worst Be with c/a ~ 1.568). In others like Zn and Cd the deviations from the ideal change the symmetry of the structure and these have a lattice parameter ratio c/a > 1.85.

#### Face centered cubic (cubic close packed)

More content relating to number of planes within structure and implications for glide/slide e.g. ductility.

#### Double hexagonal close packed

Similar to the ideal hcp structure, the perfect dhcp structure should have a lattice parameter ratio of ${\displaystyle \scriptstyle {\frac {c}{a}}=}$ ${\displaystyle \scriptstyle 4{\sqrt {\frac {2}{3}}}}$ ~ 3.267. In the real dhcp structures of 5 lanthanides (including β-Ce) ${\displaystyle \scriptstyle {\frac {c}{2a}}}$ variates between 1.596 (Pm) and 1.6128 (Nd). For the 4 known actinides dhcp lattices the corresponding number vary between 1.620 (Bk) and 1.625 (Cf).[10]

### Body centred cubic

This is not a close packed structure. In this each metal atom is at the centre of a cube with 8 nearest neighbors, however the 6 atoms at the centres of the adjacent cubes are only approximately 15% further away so the coordination number can therefore be considered to be 14 when these are included. Note that if the body centered cubic unit cell is compressed along one 4 fold axis the structure becomes face centred cubic (cubic close packed).

## References

1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
2. ^ A.F Wells (1962) Structural Inorganic Chemistry 3d Edition Oxford University Press
3. ^ Harry L. Yakel, A REVIEW OF X-RAY DIFFRACTION STUDIES IN URANIUM ALLOYS. The Physical Metallurgy of Uranium Alloys Conference, Vail, Colorado, Feb. 1974
4. ^ Lemire,R.J. et al.,Chemical Thermodynamics of Neptunium and Plutonium, Elsevier, Amsterdam, 2001
5. ^
6. ^ Lemire,R.J. et al.,2001
7. ^
8. ^
9. ^
10. ^ Nevill Gonalez Swacki & Teresa Swacka, Basic elements of Crystallography, Pan Standford Publishing Pte. Ltd., 2010
General
• Actinides and the Environment, Edited by P.A. Sterne, A. Gonis and A.A. Borovoi, NATO ASI Series, Proc. of the NATO Advanced Study Institute on Actinides and the Environment, Maleme, Crete, Greece, July 1996, Kluver Academic Publishers,. pp. 59–61. ISBN 0-7923-4968-7.
• The Chemistry of the Actinide and Transactinide Elements, Edited by L.R. Morss, Norman M. Edelstein, Jean Fuger, 3rd. Edition, Springer 2007 ISBN 1402035551. ISBN 978-1402035555.