Question

Silver (atomic weight = 108 g mol^–1) has a density of 10.5 g cm^–3. The number of silver atoms on a surface of area 10^–12 m² can be expressed in scientific notation as y x 10^x . The value of x is.

Answer 1

 Ag crystallises in FCC unit cell with 4 atoms per unit cell.

⇒ a³ (Volume of unit cell) 

⇒ Surface area of unit cell 

 = a² = 1.6 x 10^-19 m²

⇒ Number of unit cells on 10^–12 m² surface

∵ There are two atoms (effectively) on one face of unit cell 

Number of atoms on 10^–12 m² surface = 2 x number of unit cell = 1.25 x 10^{7 .} 

⇒ x = 7