The shape of the lesson
By the end of the lesson, learners can
- Groups and periods: Step across Period 3 in the simulator, from sodium to argon.
- Predicting behaviour: Extended.
- Order: increasing proton number.
- Group number = outer-shell electrons (I to VII).
- Period number = occupied shells.
- Across: metal to non-metal.
One picture every idea returns to
The Periodic Table arranges elements in order of increasing proton number. Vertical columns are groups; horizontal rows are periods. For Groups I to VII the group number equals the number of outer-shell electrons, and the period number equals the number of occupied shells. Elements change from metallic to non-metallic across a period. Extended: elements in the same group have similar chemical properties because they have the same number of outer electrons; the group number predicts the charge on the ion: I +1, II +2, III +3, V −3, VI −2, VII −1.
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 map built from electrons.. The Periodic Table is not a random list. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Groups and periods | Step across Period 3 in the simulator, from sodium to argon. Project tab 1 of the lab (Periodicity lab, trends across period 3) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Predicting behaviour | Extended. | Think-Pair-Share |
| 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 Predicting behaviour, 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.
Think-Pair-Share
Pose the question, give thirty seconds of silent thinking, then a minute to compare with a partner before a few pairs share with the class. The silent minute is the part that cannot be cut.
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 Periodic Table is ordered by proton number, not by relative atomic mass. | Argon (A r 40) comes before potassium (A r 39) because argon has 18 protons and potassium 19. And Group VIII (noble gases) has 8 outer electrons, except helium, which has 2. |
Arrangement of the Periodic Table: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
State how the elements are arranged in the Periodic Table, and name the vertical columns and horizontal rows.
Element Q has proton number 16. Give its electronic configuration, its group and its period.
Describe how the character of the elements changes across Period 3 from sodium to argon.
(Extended) Explain why elements in the same group have similar chemical properties.
(Extended) Predict the formula of the ion formed by (a) calcium, Group II, (b) nitrogen, Group V, and (c) bromine, Group VII.
Element Z is in Group I and Period 4. Predict whether Z is a metal or a non-metal, and state the number of electrons in its outer shell.
Answer key and marking notes
- In order of increasing proton number.
- Columns are groups; rows are periods.
- 2,8,6.
- Group VI.
- Period 3.
- The elements change from metals (sodium, magnesium, aluminium) to non-metals (phosphorus, sulfur, chlorine, argon).
- Silicon, in the middle, has properties between the two.
- They have the same number of electrons in their outer shell.
- Chemical reactions involve the outer electrons, so these elements react in similar ways.
- (a) Ca2+
- (b) N3−
- (c) Br−
- A metal (Group I elements are metals; it is potassium).
- One outer-shell electron.
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 statement is true for all the elements in the same period of the Periodic Table?
- ATheir atoms have the same number of occupied electron shells.
- BTheir atoms have the same number of outer-shell electrons.
- CThey have similar chemical properties.
- DThey have the same relative atomic mass.
The diagram shows an outline of part of the Periodic Table with five elements labelled A to E. Which labelled element has the electronic configuration 2,8,6?
- AB
- BA
- CD
- DE
An element has proton number 12. Where is it found in the Periodic Table?
- APeriod 3, Group II
- BPeriod 2, Group II
- CPeriod 3, Group III
- DPeriod 2, Group VIII
Which element in Period 3 has properties that are between those of a metal and a non-metal?
- Asilicon
- Baluminium
- Cphosphorus
- Dmagnesium
Tellurium (Ar = 128) is placed before iodine (Ar = 127) in the Periodic Table. What is the reason?
- ATellurium has 52 protons and iodine has 53 protons.
- BTellurium has the higher relative atomic mass.
- CElements are placed in order of their number of neutrons.
- DTellurium is a solid and iodine is a gas.
Element X is a metal in Group III. What is the most likely formula of its oxide?
- AX2O3
- BXO3
- CX3O2
- DXO
Element Y has the electronic configuration 2,8,7. Element Z is directly below Y in the Periodic Table. Why do Y and Z both react with sodium to form a compound with the formula NaY or NaZ?
- ABoth atoms have seven outer-shell electrons and gain one electron to form a 1− ion.
- BBoth atoms have the same number of electron shells.
- CBoth elements are in the same period.
- DBoth atoms lose seven electrons to form a 7+ ion.
Which pair of ions have charges correctly predicted from the group numbers of their elements?
- AAl3+ and S2−
- BMg+ and N3−
- CK2+ and Cl−
- DCa2+ and O6−
Quiz key
The period number equals the number of occupied electron shells, so every atom in a row has the same number of shells. The same number of outer-shell electrons, and the similar chemical properties that follow from it, belong to a group (a column), not a period. Relative atomic mass increases along a row; it is never the same for every element.
The configuration 2,8,6 has three occupied shells, so the element is in Period 3, and six outer-shell electrons, so it is in Group VI. That is position B (sulfur). A is in Period 2, Group I (2,1). D is in Period 2, Group VIII (2,8). E is in Period 4, Group VII, so its outer shell holds seven electrons, not six.
Twelve electrons are arranged 2,8,2 (magnesium). Three occupied shells means Period 3 and two outer electrons means Group II. Period 2 would mean only two shells; Group III would need three outer electrons; and 2,8 alone (Period 2, Group VIII) accounts for only ten of the twelve electrons.
Across Period 3 the elements change from metals (sodium, magnesium, aluminium) to non-metals (phosphorus, sulfur, chlorine, argon). Silicon sits in the middle and is a semi-metal. Aluminium and magnesium are metals, and phosphorus is a non-metal.
The Periodic Table is arranged in order of increasing proton number. Tellurium has 52 protons and iodine 53, so tellurium comes first even though its relative atomic mass is slightly higher. Ordering by relative atomic mass would put them the other way round, and ordering by neutrons is not the rule. Iodine is a grey-black solid at room temperature, not a gas.
A Group III metal loses its three outer electrons to form X3+; oxygen, in Group VI, gains two electrons to form O2−. Two X3+ (total +6) balance three O2− (total −6), giving X2O3, as in aluminium oxide Al2O3. X3O2 swaps the numbers the wrong way round; XO would suit a Group II metal; XO3 does not balance the charges.
Y is chlorine and Z is bromine; both are in Group VII with seven outer-shell electrons. Chemical reactions involve the outer electrons, so both gain one electron to complete the outer shell and form a 1− ion, giving NaCl and NaBr. Z has one more shell than Y, so they are not in the same period and do not have the same number of shells. Losing seven electrons would need far too much energy; halogens gain one.
Aluminium (Group III) loses three electrons to form Al3+, and sulfur (Group VI) gains two to form S2−. Magnesium is in Group II, so it forms Mg2+, not Mg+. Potassium is in Group I and forms K+. Oxygen gains two electrons, not six, so its ion is O2−; the group number is the number of outer electrons, not the ion charge for a non-metal.
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.