Question

An alloy of Au and Cu crystallises in a cubic lattice in which the gold atoms occupy the lattice points at the corners of a cube and the copper atoms occupy the centres of each faces of the cube. What is the empirical formula of this compound?

• A. $AuCu$
• B. $AuC{u}_3$
• C. $A{u}_{3}Cu$
• D. $A{u}_{2}C{u}_3$

Answer 1

The correct option is B $AuC{u}_3$

Au atoms are at eight corners of the cube. Thus, number of Au atoms in the unit cell $=8/8=1,Cu$ atoms are at the face centre of the six faces. Therefore, its share in the unit cell $=\frac{6}{2}=3$. Thus, formula is $AuC{u}_3$.