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 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 114 elements as well as the 118th, and predictions are given for elements that have never been produced in bulk.
Table
Among the undiscovered elements, predictions are only available for ununennium and unbinilium, which are predicted to crystallise in body-centered cubic structures like their lighter congeners.Unusual structures
| Element | crystal system | coordination number | notes |
| Mn | cubic | distorted bcc – unit cell contains Mn atoms in 4 different environments. | |
| Zn | hexagonal | distorted from ideal hcp. 6 nearest neighbors in same plane: 6 in adjacent planes 14% farther away | |
| Ga | orthorhombic | each Ga atom has one nearest neighbour at 244 pm, 2 at 270 pm, 2 at 273 pm, 2 at 279 pm. | The structure is related to that of iodine. |
| Cd | hexagonal | distorted from ideal hcp. 6 nearest neighbours in the same plane- 6 in adjacent planes 15% farther away | |
| In | tetragonal | slightly distorted fcc structure | |
| Sn | tetragonal | 4 neighbours at 302 pm; 2 at 318 pm; 4 at 377 pm; 8 at 441 pm | white tin form |
| 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. | grey metallic form. |
| Hg | rhombohedral | 6 nearest neighbours at 234 K and 1 atm | this structure can be considered to be a distorted hcp lattice with the nearest neighbours in the same plane being approx 16% farther away |
| 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. | 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.... |
| 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. | |
| Np | orthorhombic | highly distorted bcc structure. Lattice parameters: a = 666.3 pm, b = 472.3 pm, c = 488.7 pm | |
| 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° |
Usual crystal structures
Close packed metal structures
Many metals adopt close packed structures i.e. hexagonal close packed and face-centred cubic structures. 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. 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,... .
- face-centered cubic has every third layer directly above/below each other: A,B,C,A,B,C,... .
- 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.
- α-Sm packing has a period of 9 layers A,B,A,B,C,B,C,A,C,.....
Hexagonal close packed