Atoms in Crystals

Unit cells and density

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Crystals repeat a unit cell: simple cubic, BCC (2 atoms) or FCC (4 atoms).
• Density $= \frac{nM}{N_A a^3}$ links cell size, atomic mass and density.
• FCC packs 74% of space and has many slip planes, making metals ductile.

Steps

1. Repeating boxes
2. Counting FCC atoms
3. Measure the iron cell
4. How full?
5. Bendy metals
6. Density of copper