Lesson Plan: C1.5.02

Hamble Lesson Observation Plan
Learning About
What does the relative formula mass tell us?
Keywords:
  • atomic number: The total number of protons in an element. (1)
  • Mass number: Total number of protons and neutrons in an element. (1)
  • Compound: A substance consisting of atoms or ions of two or more different elements in definite proportions joined by chemical bonds into a molecule. (1)
  • Relative Formula Mass: A total of all the atomic mass values for all the atoms in a formula. (1)
Memory Anchor:
Method Precise Learning Objective Linked Question / Activity
(Designed for maximum working out)		 Stepping Stones Pitstop Check
(Thinking Map)
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. How do we calculate the relative formula mass (Mr) of a compound?

Review the definition of relative atomic mass. Recall how to find the relative atomic mass from the Periodic Table. Define the relative molecular mass. Extended writing: write instructions to another student how to calculate the relative formula mass. Model compounds with different sized and coloured lego bricks pre-marked with symbol and Ar of different elements. Sum the Ars marked on the bricks to obtain the Mr.
In a balanced chemical equation, the sum of the relative formula masses of the reactants in the quantities shown equals the sum of the relative formula masses of the products in the quantities shown. Why must the total relative formula mass of all of the reactants equal that of all of the products made?
Links To the Big Ideas
ForcesParticlesEnergyCells