1. The substance silicon is found to crystallize in a cubic lattice, with an edg

Question

1. The substance silicon is found to crystallize in a cubic lattice, with an edge length of 541.7 pm. if the density of solid silicon is 2.348 g/cm3, how many Si atoms are there per unit cell? your answer should be an integer:------- atoms

2. Solid strontium fluoride has the same kind of crystal structure as CaF2 which is pictured below:

a. How many F- ions are there per unit cell in solid strontium fluoride?

b. How many SrF2 formula units are there per unit cell?

3a. How many F- ions are there per unit cell in solid cadmiun fluoride?
3b How many F- ions are there per unit cell in solid cadmiun fluoride?

4a. How many F- ions are there per unit cell in solid cadmiun fluoride

4b. How many CdF2 formula units are there per unit cell

4c. If the edge length of the unit cell is 618.4 pm, what is the density of BaF2 in g/cm3.
g/cm3

Explanation / Answer

Calculate the volume of the cell:

V=a^3,

1 pm = 1012m = 1010cm

Vcell = (541.7 pm)3 = (541.7 x 1010 cm)3 = 1.590 x 1022 cm^3

Density of the cell=Mass of the cell/volume of the cell

Mass of the cell=2.348 g/cm3 x 1.590 x 1022 cm3 = 3.732 x 1022 g

The molecular weeight of the Si is 28.09 g/mol

convert mass in g to mass in g/atom

1 mol contains 6.023*10^23 atoms,

Mass of silicion atoms=28.09 g /mol/(6.023*10^23 1/mol)=4.665 10^-23 g/atom

Number of atom= 3.732 x 1022 g/4.665 10^-23 g/atom=8 atoms/cell

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