The Mole

 Equal volumes of different gases have a constant ratio:
Oxygen             :  Hydrogen   16:1
Carbon Dioxide :  Hydrogen   21:1

Relative Mass:
-Expressed by comparing it mathematically to mass to the mass of another object.

Avogadro's Hypothesis:
-Equal volumes of different gases at the same temperature and pressure have the same number of particles.
-If they have the same number of particles, the mass ratio is due to the mass of the particles.
-We now use this principle for the relative masses of all atoms on the periodic table.

Atomic Mass:
-The mass of a specific isotope of a given atom. Expressed as amu (atomic mass unit)

Formula Mass:
All the atoms of a formula of an ionic compound.
Example:  Potassium Fluoride
                K            +         F
                39.1        +    19.0
                KF = 58.1 amu

Molecular Mass:
-The mass of one molecule of a substance.  Expressed as amu.

Molar Mass
-Atomic/Molecular/Formula mass of any pure substance (in grams per mole)
Example: 1 mole of oxygen = 16.0 g/mol
               1 mole of carbon = 12.0 g/ml
-The molar atomic mass of an element is the mass of 1 mole of that element.
This video explains how to find molar mass:


Avogadro's Number
-The number of particles in 1 mole of any amount of substance is 6.022 x 10^23 particles/mol

-The mole is important because it allows chemist to count atoms and molecules 


A chemistry song