Is there an expansion or contraction as iron transform from HCP to BCC? The atomic radius of iron is — Solid State Chemistry Question

💡 Solution & Explanation

In HCP, atomic radius r = 125 pm. In BCC, atomic radius r = 50 × √2 pm ≈ 70.7 pm. Since the atomic radius decreases significantly from 125 pm to 70.7 pm, the volume occupied per iron atom decreases, meaning there is a contraction during this structural transition.