Dr. Anthony Haynes

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CHM1001.4: Hydrogen and the s- and p-block elements

Metallic lattice structures

Close-packed lattices

Most metals adopt either cubic or hexagonal close packed structures

Click and drag on a structure to rotate the view

Cubic-Close-Packed (CCP) also known as Face-Centred-Cubic (FCC) Note how the close-packed layers lie across the body-diagonals of the cube (ABCA... sequence) The coordination number (i.e. the number of nearest neighbours) for each atom is 12 74% of the available volume is occupied
Hexagonal-Close-Packed (HCP) 4 layers shown (ABAB... sequence) If you rotate the structure to view it from above or below you can see channels formed by the alignment of octahedral holes The coordination number for each atom is 12, as for the CCP structure above 74% of the available volume is occupied

For the mathematically inclined, the close packing of spheres is the subject of the long standing Kepler Conjecture,for which a proof has recently been published



Non-close-packed lattices

Body Centred Cubic (BCC) The coordination number for each atom is 8 68% of the available volume is occupied Examples: metals of groups 1, 5, 6, Ba, Fe
Simple Cubic The coordination number for each atom is 6 52% of the available volume is occupied Example: polonium

Also see an excellent resource on Solid State Structures from the University of Sydney