Atomic Mass and Molecular Mass

Atomic Mass and Molecular Mass

Atomic Mass

• Atomic mass is the mass of a single atom compared to 1/12th of the mass of a carbon-12 atom.

• Example:

  • Hydrogen: 1 u

  • Oxygen: 16 u

Molecular Mass

• The sum of the atomic masses of all atoms in a molecule.

Example Calculation of Molecular Mass:

• Water (H₂O)

  • H = 1u, O = 16u

  • Molecular Mass = (2 × 1) + 16 = 18 u

• Carbon Dioxide (CO₂)

  • C = 12u, O = 16u

  • Molecular Mass = 12 + (2 × 16) = 44 u

(Diagram: Molecular mass calculations for H₂O, CO₂, etc.)

Formula Unit Mass

• The formula unit mass is the sum of the atomic masses of ions in an ionic compound.

Example Calculation:

• Sodium Chloride (NaCl)

  • Na = 23u, Cl = 35.5u

  • Formula Unit Mass = 23 + 35.5 = 58.5 u

• Calcium Carbonate (CaCO₃)

  • Ca = 40u, C = 12u, O = 16u

  • Formula Unit Mass = 40 + 12 + (3 × 16) = 100 u

(Diagram: Calculation examples for NaCl, CaCO₃)