The Mole (Cambridge (CIE) O Level Chemistry): Revision Note

The Mole & the Avogadro Constant

The Mole & Avogadro's Constant

• Chemical amounts are measured in moles

• The mole, symbol mol, is the SI unit of amount of substance

• One mole of a substance contains the same number of the stated particles, atoms, molecules, or ions as one mole of any other substance

• One mole contains 6.02 x 10²³ particles (e.g. atoms, ions, molecules); this number is known as the Avogadro constant

• For example:

  • One mole of sodium (Na) contains 6.02 x 10²³ atoms of sodium

    • One mole of hydrogen (H₂) contains 6.02 x 10²³ molecules of hydrogen

    • One mole of sodium chloride (NaCl) contains 6.02 x 10²³ formula units of sodium chloride

• The mass of 1 mole of a substance is known as the molar mass

• For an element, it is the same as the relative atomic mass written in grams

• For a compound, it is the same as the relative formula mass or relative molecular mass in grams