Periodic table (crystal structure)

For elements that are solid at standard temperature and pressure the first table gives the crystalline structure of the most thermodynamically stable form(s) in those conditions. Each element is shaded by a color representing its respective Bravais lattice, except that all orthorhombic lattices are grouped together.

Melting point and standard pressure
The second table gives the most stable structure of each element at its melting point. (H, He, N, O, F, Ne, Cl, Ar, Kr, Xe, and Rn are gases at STP; Br and Hg are liquids at STP.) Note that helium does not have a melting point at atmospheric pressure, but it adopts a magnesium-type hexagonal close-packed structure under high pressure.

Predicted structures
Predictions are given for elements 85–87, 100–113 and 118; all but radon have not been produced in bulk. Probably Cn and Fl are liquids at STP. Calculations have difficulty replicating the experimentally known bcc structures of the stable alkali metals, and the same problem affects Fr (87); nonetheless, it is probably also bcc. The latest predictions for Fl (114) could not distinguish between face-centred cubic and hexagonal close-packed structures, which were predicted to be close in energy. No predictions are available for elements 115–117.

Structure types
The following is a list of structure types which appear in the tables above. Regarding the number of atoms in the unit cell, structures in the rhombohedral lattice system have a rhombohedral primitive cell and have trigonal point symmetry but are also often also described in terms of an equivalent but nonprimitive hexagonal unit cell with three times the volume and three times the number of atoms.

Close packed metal structures
The observed crystal structures of many metals can be described as a nearly mathematical close-packing of equal spheres. A simple model for both of these is to assume that the metal atoms are spherical and are packed together as closely as possible. 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. The following types can be viewed as a regular buildup of close-packed layers:
 * Mg type (hexagonal close packing) has alternate layers positioned directly above/below each other: A,B,A,B,...
 * Cu type (face-centered cubic) has every third layer directly above/below each other: A,B,C,A,B,C,...
 * α-La type (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 type has a period of 9 layers A,B,A,B,C,B,C,A,C,...

Precisely speaking, the structures of many of the elements in the groups above are slightly distorted from the ideal closest packing. While they retain the lattice symmetry as the ideal structure, they often have nonideal c/a ratios for their unit cell. Less precisely speaking, there are also other elements are nearly close-packed but have distortions which have at least one broken symmetry with respect to the close-packed structure:


 * In type is slightly distorted from a cubic close packed structure
 * α-Pa type is distorted from a hexagonal close packed structure