318923 Total volume of atoms present in a face-centred cubic unit cell of a metal is ( r is atomic radius)
The face centred cubic unit cell contains 4 atoms∴ Total volume of atoms =4×43πr3=163πr3
318924 The empty space left in a hexagonal close packing of spheres in three dimensions is
Empty space in a HCP arrangement =100- Packing efficiency =100−74=26%
318925 The number of atoms in 4.5 g of a face-centred cubic crystal with edge length 300 pm is:(Given density =10 g cm−3 and NA=6.022×1023 )
d=Z×MNA×a3⇒M=10×6.022×1023×(300×10−10)34M=40.5gmTherefore atoms 40.5gm→6.022×10234.5gm→xx=6.6×1022 atoms(or) d=ZMNA⋅a3(or) No. of atoms =Z× mass of crystal d×a=4×4.510×(300×10−10)3=6.6×1022 atoms
318926 In which pair most efficient packing is present?
Packing efficiency of HCP and CCP is 74%.
318927 The percentage packing efficiency of bcc lattice is x% and the percentage packing efficiency of simple cubic lattice is y%.The value of (x−y) is
Percentage packing efficiency:bcc lattice =68%Simple cubic lattice =52.4%∴x−y=68−52.4=15.6