When two or more atoms combine they give rise to a molecule. A molecule can be made up of many atoms of the same element. There are 112 elements known to man, so can you imagine the different permutations and combinations of molecules...

The ideal gas law is an empirical law; it's a relationship between the pressure in a system of gases to the volume, the temperature, and the number of gas atoms/molecules in the system. This "law" is valid if the gas atoms/molecules are...