8. Solve Problem 10, Chapter XVIII, without using molecular weights. Compare your results.
9. The specific heat of aluminium is 0.214; of lead is 0.031. From these specific heats calculate the atomic weights of each of the elements.
CHAPTER XX
THE PHOSPHORUS FAMILY
| SYMBOL | ATOMIC WEIGHT | DENSITY | MELTING POINT | |
| Phosphorus | P | 31.0 | 1.8 | 43.3° |
| Arsenic | As | 75.0 | 5.73 | — |
| Antimony | Sb | 120.2 | 6.7 | 432° |
| Bismuth | Bi | 208.5 | 9.8 | 270° |
The family. The elements constituting this family belong in the same group with nitrogen and therefore resemble it in a general way. They exhibit a regular gradation of physical properties, as is shown in the above table. The same general gradation is also found in their chemical properties, phosphorus being an acid-forming element, while bismuth is essentially a metal. The other two elements are intermediate in properties.
Compounds. In general the elements of the family form compounds having similar composition, as is shown in the following table:
| PH3 | PCl3 | PCl5 | P2O3 | P2O5 |
| AsH3 | AsCl3 | AsCl5 | As2O3 | As2O5 |
| SbH3 | SbCl3 | SbCl5 | Sb2O3 | Sb2O5 |
| BiCl3 | BiCl5 | Bi2O3 | Bi2O5 |