Silicon used in computer chips must have an impurity level below 10-9 (that is, fewer than...

Silicon used in computer chips must have an impurity level below 10-9 (that is, fewer than one impurity atom for every 109 Si atoms). Silicon is prepared by the reduction of quartz (SIO2) with coke (a form of carbon made by the destructive distillation of coal) at about 2000°C:

Next, solid silicon is separated from other solid impurities by treatment with hydrogen chloride at 350°C to form gaseous trichlorosilane (SiCl3H):

Finally, ultrapure Si can be obtained by reversing the above reaction at 1000°C:

The molar heat of vaporization of trichlorosilane is 28.8 kJ/mol and its vapor pressure at 2°C is 0.258 atm. (a) Using this information and the equation

determine the normal boiling point of trichlorosilane. (b) What kind(s) of intermolecular forces exist between trichlorosilane molecules? (c) Each cubic unit cell (edge length a = 543 pm) contains eight Si atoms. If there are 1.0 × 1013 boron atoms per cubic centimeter in a sample of pure silicon, how many Si atoms are there for every B atom in the sample? (d) Calculate the density of pure silicon.