Atoms at corners and face centers, coordination number 12 and packing efficiency 74 percent.
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The face-centred cubic structure has atoms at the corners and at the centre of each of the six faces of a cube, giving four atoms per unit cell. Atoms touch along the face diagonal, so 4r = √2 a, and each atom has a coordination number of twelve. Its packing efficiency is √2π/6, about 74 percent, which is the maximum possible for equal spheres. The layers stack in an ABCABC sequence, and the structure is also called cubic close packing. Many common metals, including copper, silver, gold and aluminium, adopt it.
Key ideas: Relationships: face diagonal sqrt(2) a = 4r, so a = 2 sqrt(2) r = 2.828 r. Z = 4, packing 0.740. There are 4 octahedral voids and 8 tetrahedral voids per cell. Density = 4M / (NA a^3). Slip planes are the close-packed (111) planes, making fcc metals ductile.
Common mistakes and connections: Students use body diagonal for fcc or count only 3 atoms in the cell. Another confusion is calling it cubic close packed and thinking it differs from ccp; they are the same. Atoms along the cube edge do not touch each other. Links to hcp, voids, ionic structures like NaCl and ductility of metals.
FCC (cubic close packed): four atoms per unit cell, coordination number 12 and 74% packing efficiency, found in Cu, Al, Ag and Au. The interactive lesson shows this as a live animation or chart.
Copper, silver, gold and aluminium are all face-centred cubic metals.
Atoms at corners and face centers, coordination number 12 and packing efficiency 74 percent.
Face-Centered Cubic is a intermediate topic in States of Matter & Solutions. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in States of Matter & Solutions first: Unit Cell, Simple Cubic Lattice, Body-Centered Cubic.
The next topics in States of Matter & Solutions are Hexagonal Close Packing and Packing Efficiency.
Yes. The interactive lesson includes a self-check question on Face-Centered Cubic, and the States of Matter & Solutions quiz draws on every topic in this area.
Face-Centered Cubic is topic 60 of 109 in States of Matter & Solutions.