Question

The substance calcium is found to crystallize in a cubic lattice, with an edge length of 556.0 pm. If the density of solid calcium is 1.549 g/cm³, how many Ca atoms are there per unit cell?

Your answer should be an integer:______ atoms

Answer 1

Vol of Ca unit cell = (556pm)³ = (5.56A^o)³ = 171.879 X 10^-24 cm³

Density of Ca = m/V = 1.549 g/cm³

1cm³                                    ======= 1.549 g

171.879 X 10^-24 cm³ ======= ?

? = 1.549X171.879 = 266.24 X 10^-24 g

Ca molecular weight = 40.078g/mol (means)

40.078g          ====== 6.023X 10²³

266.24X10^-24g   ======    ?

? = 4atoms