Moles

Mole is a unit like milometers, seconds, or litres.

A long time ago, scientists studied different gases and determined their properties.

They found the masses of hydrogen, oxygen, and carbon dioxide.

By finding the mass, they also discovered that if the gases had the same volume, they have the same ratios

Oxygen : Hydrogen = 16:1

Carbon Dioxide : Hydrogen = 22:1

Carbon Dioxide : Oxygen = 11:8

Different Types of Masses:

Relative Mass: a comparison (mathematically) between the mass of two objects

Hydrogen and Oxygen were all previously used as a standard for comparison but now, we use CARBON (mass= 12amu)as the standard for comparison.

Avogadro is a scientist that recognized the pattern and created:

 AVOGADRO'S HYPOTHESIS

Equal volumes of different gases at the same temperature and pressure have he same number of particles

If the number of particles are the same, that means the mass ratio is due to the mass of the particles.

This principle was then used to create the periodic table.

Atomic Mass: mass of 1 atom of an element in atomic mass units

Example: Sodium has an atomic mass of 23.0 amu

Formula Mass: Mass of all the atoms in an ionic compound

Example: NaCl (salt)

Na = 23.0 amu

Cl = 35.5 amu

23.0 + 35.5 = 58.5 amu

Molecular Mass: Mass of all the atoms in a covalent compound

Example: CO

Carbon = 12.0 amu

                                                        Oxygen = 16.0 amu

                                                       12.0 + 16.0 = 28.0 amu

Molar Mass: Mass of one mole of each element

Example: 1 mole of oxygen = 16.0g/mol

1 mole of fluorine = 19.0 g/mol

Avogadro's number : 6.022x10^23

This is the number of particles in 1 mole of a substance.

The mole is just a unit like kilometers and meters and when it is used to express the molar mass of an atom, the unit for mole is grams/mol.

The mole is important because it allows chemists to use their mass to calculate how much atoms and molecules there are instead of actually counting them.

To give you an idea of how big one mole is, here is a video.