The shape of the lesson
By the end of the lesson, learners can
- Inside the atom: Build an atom in the simulator.
- Proton number and mass number: The symbol 23 11 Na carries two numbers.
- Shells and the Periodic Table: Fill the shells in order, 2 then 8 then 8, and the Periodic Table's layout appears on its own.
- Protons = proton number; electrons = protons in a neutral atom.
- Neutrons = mass number − proton number.
- Shells fill 2, 8, 8 for the first 20 elements.
- Outer electrons = group (I to VII); shells = period.
One picture every idea returns to
An atom has a small central nucleus of protons and neutrons, surrounded by electrons in shells. The proton number (atomic number) is the number of protons; in a neutral atom it also equals the number of electrons. The mass number (nucleon number) is protons plus neutrons. Electrons fill shells in order: 2 in the first, then 8, then 8 for the first 20 elements. The number of outer-shell electrons gives the group (I to VII), and the number of occupied shells gives the period.
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, A tiny nucleus, a cloud of shells.. Every atom has the same three ingredients: protons, neutrons and electrons. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Inside the atom | Build an atom in the simulator. Project tab 1 of the lab (Atomic structure lab, atom and ion builder) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Proton number and mass number | The symbol 23 11 Na carries two numbers. | Pairs |
| 21 to 30 min | Teach and check: Shells and the Periodic Table | Fill the shells in order, 2 then 8 then 8, and the Periodic Table's layout appears on its own. | Corners |
| 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, 16 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 Shells and the Periodic Table, 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.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
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 mass number is not the number of neutrons. | It counts protons and neutrons together, so always subtract: neutrons = mass number − proton number. Also check which number is which: the mass number is always the larger one. |
Atomic structure and the Periodic Table: worksheet
6 questions, 16 marks. Written in the style of the papers; no past paper question is reproduced.
Copy and complete: give the relative charge and relative mass of a proton, a neutron and an electron.
Define proton number and mass number.
For an atom of 3919K, state the number of protons, neutrons and electrons, and write its electronic configuration.
Element X has the electronic configuration 2,8,3. State its group and period, and identify the element.
An atom contains charged particles. Explain why the atom has no overall charge.
An atom of element Y has mass number 40 and contains 22 neutrons. Identify Y, give its electronic configuration and explain whether it is likely to be reactive.
Answer key and marking notes
- Proton: relative charge +1, relative mass 1.
- Neutron: relative charge 0, relative mass 1.
- Electron: relative charge −1, relative mass 1/1836.
- Proton number: the number of protons in the nucleus of an atom.
- Mass number: the total number of protons and neutrons in the nucleus of an atom.
- 19 protons and 19 electrons.
- 39 − 19 = 20 neutrons.
- Configuration 2,8,8,1.
- Three outer-shell electrons: Group III.
- Three occupied shells: Period 3.
- 2 + 8 + 3 = 13 electrons, so proton number 13: aluminium.
- The number of electrons equals the number of protons.
- Each proton has charge +1 and each electron −1, so the charges cancel (neutrons have no charge).
- Protons = 40 − 22 = 18, so Y is argon.
- Configuration 2,8,8.
- Its outer shell is full, so it is a noble gas and is unreactive.
8 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.
Which particle has a relative charge of +1 and a relative mass of 1?
- Aa proton
- Ba neutron
- Can electron
- Dan atom of hydrogen
The diagram shows the arrangement of the electrons in a neutral atom. Which element is it?
- Aphosphorus
- Bnitrogen
- Csulfur
- Dsilicon
An atom has a mass number of 35 and contains 18 neutrons. How many electrons does it have?
- A17
- B18
- C35
- D53
Magnesium has proton number 12. In which group and period of the Periodic Table is it?
- AGroup II, Period 3
- BGroup II, Period 2
- CGroup III, Period 2
- DGroup VIII, Period 2
Which statement about the structure of an atom is correct?
- AAlmost all of the mass of the atom is in the nucleus
- BThe nucleus takes up most of the volume of the atom
- CThe electrons are in the nucleus together with the protons
- DNeutrons carry a negative charge that balances the protons
Element Q is in Group VII and Period 3 of the Periodic Table. What is the electronic configuration of an atom of Q?
- A2,8,7
- B2,7
- C2,8,3
- D2,8,8,7
Which two elements have the same number of electrons in their outer shell? (Proton numbers are given in brackets.)
- Asodium (11) and potassium (19)
- Bsodium (11) and magnesium (12)
- Cneon (10) and sodium (11)
- Dcarbon (6) and oxygen (8)
The number of occupied electron shells in an atom is equal to the element's:
- Aperiod number
- Bgroup number
- Cproton number
- Dmass number
Quiz key
A proton has relative charge +1 and relative mass 1. A neutron also has relative mass 1 but no charge. An electron has charge −1 and a tiny relative mass (1/1836). A hydrogen atom has mass about 1, but it is neutral because its one electron cancels the charge of its one proton.
The configuration is 2,8,5, so there are 2 + 8 + 5 = 15 electrons. A neutral atom has equal numbers of protons and electrons, so the proton number is 15: phosphorus. Nitrogen (2,5) also has five outer electrons, and so is in the same group, but only has two shells. Sulfur (2,8,6) has 16 electrons and silicon (2,8,4) has 14.
Protons = mass number − neutrons = 35 − 18 = 17. In a neutral atom, electrons = protons = 17 (this is chlorine). 18 is the number of neutrons, 35 is the mass number, and 53 comes from adding the mass number and the neutrons.
12 electrons are arranged 2,8,2. Two outer electrons put magnesium in Group II; three occupied shells put it in Period 3. Period 2 would mean only two shells. Group VIII would need a full outer shell, which comes from reading the 8 in the second shell as the outer shell.
Protons and neutrons (relative mass 1 each) are in the nucleus, and electrons have almost no mass, so nearly all the mass is in the nucleus. The nucleus is tiny compared with the atom; most of the atom is the space occupied by the electron shells. Electrons are in shells, not in the nucleus, and neutrons have no charge: it is the electrons that balance the protons.
Period 3 means three occupied shells and Group VII means seven outer electrons: 2,8,7 (chlorine). 2,7 has only two shells, so it is fluorine in Period 2. 2,8,3 swaps the group and period numbers, and 2,8,8,7 has four shells, which would be Period 4.
Sodium is 2,8,1 and potassium is 2,8,8,1: both have one outer electron, which is why they are both in Group I. Magnesium (2,8,2) has two; neon (2,8) has a full outer shell of eight; carbon (2,4) has four and oxygen (2,6) has six. Elements next to each other in a period differ by one outer electron.
Each new period starts when electrons begin to fill a new shell, so the number of occupied shells equals the period number. The group number is linked to the number of outer-shell electrons. The proton number equals the total number of electrons, and the mass number counts protons plus neutrons.
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.