Unit Cells?

• Use to teach stoichiometry.

• Two possible unit cells for the structure are shown with dashed lines.

• The dots could represent the Na⁺ ions and the open circles Cl^- ions.

• Smaller unit cell has one each of the two types of atoms.

• The larger unit cell has four each of the two types of atoms.

• Both give a stoichiometric ratio of 1:1, the ratio of atoms in the empirical formula.