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Given that the ionic radius of Li+ is 60 pm and that of F- is 136 pm, what crystal structure does LiF adopt and what is its coordination number?

1. Same as NaCl, coordination number 6
2. Same as CsCl, coordination number 8
3. Antifluorite type, coordination number 8
4. None of the above

Correct answer: Same as NaCl, coordination number 6

Solution

Li+/F- radius ratio = 60/136 = 0.44, which lies in the 0.414-0.732 octahedral range, so LiF takes the NaCl (rock-salt) structure with coordination number 6, not the antifluorite type.

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