Valency

To study the nature of different chemicals requires knowledge of the fundamental building blocks of all chemicals, the molecule.

Explain the following term:

Compound  

The valency of hydrogen is

Write the valency of the following radicals and represent them by a putting a positive or a negative sign. 

${\mathrm{CO}}_3, {\mathrm{SO}}_4, \mathrm{Cl}, {\mathrm{PO}}_4, \mathrm{Al}, \mathrm{Na}, \mathrm{Ca}, \mathrm{Mg}.$

What are monatomic and diatomic molecules?

State the combining capacities of aluminium and oxygen in ${\mathrm{Al}}_2{\mathrm{O}}_3$.