The shape of the lesson
By the end of the lesson, learners can
- Read the numbers: Change the proton and neutron counts and watch the nuclide notation update.
- Count from the notation: The two numbers give the protons and the total, and neutrons follow by subtraction.
- Protons: the bottom number (proton number Z).
- Neutrons: top minus bottom (A - Z).
- Electrons: equal to protons in a neutral atom.
One picture every idea returns to
A nuclide is written with the nucleon number on top and the proton number below, before the element symbol. The proton number is the number of protons, the number of neutrons is the nucleon number minus the proton number, and in a neutral atom the electrons equal the protons.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Counting the nucleus.. Two small numbers beside an element symbol tell you everything about its nucleus: how many protons it has, and how many particles in total. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Read the numbers | Change the proton and neutron counts and watch the nuclide notation update. Project tab 2 of the lab (Nuclide notation) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Count from the notation | The two numbers give the protons and the total, and neutrons follow by subtraction. Model the worked example Worked example on the board, one line at a time. | Frayer Model |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 14 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Count from the notation, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Frayer Model
Pairs fill a four-box grid for the key term: definition, characteristics, examples and non-examples. The non-examples box is where the misconceptions surface, so give it the most time.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| The bottom number is the proton number Z and the top number is the nucleon number A. | The neutron number is not written directly. Find it by subtracting: neutrons = A minus Z. |
Protons, neutrons and nuclide notation: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
State the relative charge of a proton, a neutron and an electron.
Compare the relative mass of an electron with the relative mass of a proton.
A neutral atom has a nucleon number of 19 and a proton number of 9. State the number of protons, neutrons and electrons it contains.
Define the proton number and the nucleon number of an atom.
Atom X has 8 protons. Atom Y has 9 protons. Explain why X and Y must be different elements.
An atom of nucleon number 7 and proton number 3 loses one electron to become an ion. State the charge of the ion and explain why.
Answer key and marking notes
- Proton: charge +1. ✓
- Neutron: charge 0 (no charge). ✓
- Electron: charge -1. ✓
- A proton has a relative mass of 1. ✓
- An electron is far lighter, about 1/1840 of a proton, so its mass is almost nothing. ✓
- Protons = 9. ✓
- Neutrons = A - Z = 19 - 9 = 10. ✓
- Electrons = 9 (neutral atom). ✓
- The proton number is the number of protons in the nucleus. ✓
- The nucleon number is the total number of protons and neutrons in the nucleus. ✓
- The element is decided by the proton number. ✓
- X and Y have different proton numbers, so they are different elements. ✓
- The ion has a charge of +1. ✓
- It now has 3 protons but only 2 electrons, so there is one more positive charge than negative. ✓
3 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
In nuclide notation, the top number written before the chemical symbol is the nucleon number. What does it count?
- Athe total number of protons and neutrons in the nucleus
- Bthe number of protons only
- Cthe number of neutrons only
- Dthe number of electrons
An atom of sodium has nucleon number 23 and proton number 11. How many neutrons are in its nucleus?
- A12
- B11
- C23
- D34
A helium nucleus has nucleon number 4 and proton number 2. What does it contain?
- A2 protons and 2 neutrons
- B4 protons and 2 neutrons
- C2 protons and 4 neutrons
- D4 protons and 4 neutrons
Quiz key
The nucleon number A counts all the particles in the nucleus, that is protons plus neutrons. The lower number, the proton number Z, counts just the protons.
Neutrons = A − Z = 23 − 11 = 12. Option C is the nucleon number and B is the proton number, not the neutron count.
There are 2 protons (the proton number) and 4 − 2 = 2 neutrons. A helium nucleus is therefore 2 protons and 2 neutrons, which is also an alpha particle.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.