$2$B$\mathrm{.}1$ METALLIC CRYSTAL STRUCTURES $(10$ pts$)$

You are studying a new pure metal, Floridium, which has an FCC crystal structure. You have already

determined some useful information:

Name: Floridium

Symbol: Fo

Atomic Number: $78$

Atomic Weight: $195\mathrm{.}1\frac{g}{m}ol$

Density at $20C$:$21\mathrm{.}45\frac{g}{c}{m}^3($measured$)$

Atomic Radius: $0\mathrm{.}139$ nm

a$)$ Determine the unit edge length, $a,$ in nm using the atomic radius. $(6$ pts$)$

b$)$ Calculate the theoretical density and compare it to the measured density provided $(10$ pts$)$