Mole

The mole is a unit of measurement used in chemistry to express of a chemical substance.



Avogadro's Hypothesis:
Two equal volumes of gas, at the same temperature and pressure, contain the same number of molecules.

Avogadro's Law: 

At a constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of that gas.

Avogadro's Number:
6.022*10^23 particles/mole



Atomic Mass:
the mass of a specific isotope, expressed in atomic mass unit (amu)
Formula Mass:
the mass of all atoms of an ionic compound (in amu)
Molecular Mass:
the mass of all atoms of a covalent compound (in amu)

Example:

What is the relative mass formula of sodium chloride? (Relative atomic masses: Na = 23, Cl = 35.5)

Solution:

Sodium Chloride is an ionic solid with the formula Na⁺Cl^-.
The relative mass formula of sodium chloride is

Example:

What is the relative mass formula of water? (Relative atomic masses: H = 1, O = 16)

Solution:

The formula for water is H₂O. Each molecule contains 2 hydrogen atoms and 1 oxygen atom.
The relative mass formula of water is