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NCERT Class XII Chemistry
Chapter - The Solid State
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Question : 14 of 50
Marks: +1, -0
If the radius of the octahedral void is r and radius of the atoms in close- packing is R, derive relation between r and R.
Solution:  
R and r are the radii of the octahedral site and atoms respectively,
then from Pythagoras theorem we get
AC2=AB2+BC2A C^{2}=A B^{2}+B C^{2}
(2R)2=(R+r)2+(R+r)2(2R)^{2}=(R+r)^{2}+(R+r)^{2}
or   2R=R+r\; \sqrt{2} R = R + r
⇒(2−1)R=r\Rightarrow (\sqrt{2} - 1) R = r
∴  r=0.414R\therefore \; r = 0.414 R
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