The coinage metals—copper, silver, and gold—crystallize in a cubic closest packed structure. Use the density of copper (8.95 g/cm³) and its molar mass (63.55 g/mol) to calculate an approximate atomic radius for copper.



Answer :

The cubic closest packet structure is a face-centered cubic cell in which atoms are on corners and faces.

Each atom on the corner is shared between 8 cells and each atom at the face is shared between 2 cells so the number of atoms per unit cell

8x1/8+6x1/2=1+3=4

The volume of the unit cell can be calculated from density.

d=m/V

m is mass of unit cell

m=4 xm(Cu)

m(Cu)=mass of one Cu atom=M(Cu)/NA=63.55 (g/mol)  / ( 6.10 ^23 x1/ mol)

=10.59x 10^−23 g

V=m/d=42.37x10−23 g  /   8.95( g/cm3) =4.733⋅10−23 cm3

The edge of the unit cell is equal to:

a= 3√V

=√47.33x10−24cm3  

=3.62x 10−8 cm

=3.62x10−8 cm x 1 m  /100 cmx 10^12 pm /1 m

=362 pm

radius of the copper : 4r^2 =a^2+a^2

16r^2=2a^2

8r^2=a^2

r=​√a^2/8   =√(362)^2/8

where a =362   =127.9pm​

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