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Question
Gold (atomic radius = 0.144 nm) crystallises in a face-centred unit cell. What is the length of a side of the cell?
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Solution
For a face-centred unit cell:
`a = 2 sqrt 2 r`
It is given that the atomic radius, r = 0.144 nm
So, `a = 2 sqrt 2 xx 0.144` nm
= 2 × 1.414 × 0.144 nm ...`(∴ sqrt2 = 0.414)`
= 0.407 nm
Hence, length of a side of the cell = 0.407 nm
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