The Mole

• Scientists in early days found masses for hydrogen, oxygen and carbon dioxide.
• Discovered that equal volumes of different gases have a constant ratio. For example, oxygen : hydrogen 16:1

Relative Mass

• Is expressed by comparing it mathematically to the mass of another thing.
• Hydrogen and oxygen were used as standard for comparison.
• Now, carbon is used as standard. Assigned "12" amu therefore the mass of 1 atom = 1/12 the mass of carbon.

Avogadro's Hypothesis

• Equal volumes of different gases at the same temperature and pressure have the same number of particles. Which means that their mass ratio is due to mass of the particles.

Formula Mass

• All atoms of a formula is ionic (in amu)

Molecular Mass

• All atoms of formula in a covalent compound (in amu)

Molar Mass

• Mass of one mole of each element (in g/mol)
• The atomic/ molecular/ formula mass of any pure substance
• Eg. 1 mole of oxygen = 16.0g/mol ALL OF THESE HAVE THE SAME NUMBER OF PARTICLES.

Avogadro's Number

• The number of particles in a mole of any amount of substance
• 6.022 x 10^23 particles/ mole
• Is a counting unit like a dozen.
• Eg. A mole of atoms equals 6.022 x 10^23 atoms.