Science lesson plan · 10th grade (Year 11 in England) · 45 minutes
Relative formula mass
Atoms, elements and the periodic table
CCSS NGSS.HS-PS1-7England: KS4 Combined Science: Chemical changes (quantitative chemistry)
Objective and success criteria
Students will: Relative formula mass.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Chemical formulae
Leads to: Atom economy and greener reactions; Percentage by mass of an element in a compound
Materials: Periodic tables, Atom model kits, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Chemical formulae). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- How many atoms in total are in one molecule (formula unit) of calcium carbonate, CaCO₃? → 5Prompt: A small number after a symbol tells you how many of that atom.
- How many oxygen atoms (O) are in Al₂O₃? → 3Prompt: Find every O in the formula.
- How many different elements are in sodium hydroxide, NaOH? → 3Prompt: Count the different symbols. Each starts with a capital letter.
Hook · 5 min
- Show the periodic table and ask what patterns students can see before anything is explained.
- Share the objective: Relative formula mass. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Calculate the relative formula mass (Mr) of COâ‚‚. Relative atomic masses: C = 12, O = 16.
- Step 1: 1 × 12 + 2 × 16 = 44
- Step 2: So the answer is: 44
- Answer: 44
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Calculate the relative formula mass (Mr) of NaCl. Relative atomic masses: Na = 23, Cl = 35.5. → 58.5Prompt: Multiply each relative atomic mass by the number of those atoms.
- Calculate the relative formula mass (Mr) of aluminium (aluminum) oxide, Al₂O₃. Relative atomic masses: Al = 27, O = 16. → 102Prompt: Count the atoms of each element first, including any brackets.
You do: independent practice · 10 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Calculate the relative formula mass (Mr) of ethanol, C₂H₅OH. Relative atomic masses: C = 12, H = 1, O = 16. → 46Prompt: Count the atoms of each element first, including any brackets.
- What is the percentage by mass of calcium in CaCO₃? Relative atomic masses: Ca = 40, C = 12, O = 16. Give 1 decimal place. → 40 %Prompt: Work out Mr first.
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: Chemical formulae.
- Use concrete materials: periodic tables.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Atom economy and greener reactions; Percentage by mass of an element in a compound.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-10.
Free lesson plan from eurekami.com/lesson-plan-builder