Science lesson plan · 8th grade (Year 9 in England) · 45 minutes
Chemical formulae
Atoms, elements and the periodic table
CCSS NGSS.MS-PS1-1England: KS3 Chemistry: Atoms, elements and compoundsEngland: KS4 Combined Science: Chemical changes
Objective and success criteria
Students will: Chemical formulae.
- 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: Elements, compounds and mixtures
Leads to: Relative formula mass; Count the atoms in a chemical formula; Build ionic formulae from ion charges
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 (Elements, compounds and mixtures). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Is soil an element, a compound or a mixture? (element / compound / mixture) → mixturePrompt: How many types of atom are there?
- Sodium is a reactive metal and chlorine is a poisonous gas. What is sodium chloride like? (exactly like sodium / table salt, which is safe to eat in small amounts / a shiny metal / a poisonous gas) → table salt, which is safe to eat in small amountsPrompt: A compound can be very different from its elements.
- Elements and compounds: which statement is NOT true? (A compound contains two or more elements chemically joined. / Mixtures can be separated by physical methods such as filtering. / A compound has the same properties as its elements. / Air is a mixture.) → A compound has the same properties as its elements.Prompt: Is water made of one kind of atom?
Hook · 5 min
- Show the periodic table and ask what patterns students can see before anything is explained.
- Share the objective: Chemical formulae. 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: How many atoms in total are in one molecule (formula unit) of sodium hydroxide, NaOH?
- Step 1: Na: 1, O: 1, H: 1
- Step 2: 1 + 1 + 1 = 3
- Step 3: So the answer is: 3
- Answer: 3
- 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.
- How many atoms in total are in one molecule (formula unit) of ammonia, NH₃? → 4Prompt: A small number after a symbol tells you how many of that atom.
- How many sulfur atoms (S) are in (NH₄)₂SO₄? → 1Prompt: Find every S in the formula.
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.
- How many atoms in total are in one molecule (formula unit) of sodium hydroxide, NaOH? → 3Prompt: A small number after a symbol tells you how many of that atom.
- How many magnesium atoms (Mg) are in MgO? → 1Prompt: Find every Mg in the formula.
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: Elements, compounds and mixtures.
- 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: Relative formula mass; Count the atoms in a chemical formula; Build ionic formulae from ion charges.
- 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-8.
Free lesson plan from eurekami.com/lesson-plan-builder