Question

The coordination number for an octahedral site in pure copper is ____.

• A. 4
• B. 6
• C. 8
• D. 12

Hint:

Remember: In FCC, lattice atom coordination = 12, octahedral site coordination = 6, tetrahedral site coordination = 4.

Answer 1

The Correct Option is B

Step 1: Crystal structure of copper.
Copper crystallizes in an FCC (Face-Centered Cubic) structure. In FCC, atoms form both tetrahedral and octahedral interstitial sites. Step 2: Define octahedral site.
An octahedral site is surrounded by 6 host atoms at equal distances along the Cartesian axes, forming an octahedral geometry. Thus, the coordination number of an octahedral site = 6. Step 3: Check options.
- (A) 4 → This is for a tetrahedral site, not octahedral.
- (B) 6 → Correct for octahedral site.
- (C) 8 → Not relevant to FCC interstitial sites.
- (D) 12 → Coordination number of an FCC lattice atom itself, not interstitial site. Step 4: Conclude.
Hence, the coordination number of an octahedral site in FCC copper is: \[ \boxed{6} \]