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The Solid State

Question
CBSEENCH12010241

Silver crystallizes in face-center cubic unit cell. Each side of this unit cell has a length of 400 pm. Calculate the radius of the silver atom. (Assume the atoms just touch each other on the diagonal across the face of the unit cell. That is each face atom is touching the four corner atoms.) 

Solution

Given, silver crystallizes in fcc unit cell 
So, 
space straight r equals space fraction numerator straight a over denominator 2 square root of 2 end fraction

Where space straight r space is space the space radius space of space the space solver space atom space and space straight a space is space the space edge space length
Now comma space edge space length space equals space 400 pm space equals space 400 space straight x space 10 to the power of negative 10 end exponent space cm

Thus comma

straight r space fraction numerator 400 space straight x space 10 to the power of negative 10 end exponent over denominator 2 space straight x space 1.414 end fraction space equals space 141.44 space straight x space 10 to the power of negative 10 end exponent cm space equals space 141.4 space pm

Thus comma space the space radius space of space the space silver space atoms space was space found space to space be space 141.4 space pm