The shape of the lesson
By the end of the lesson, learners can
- Configurations and the definition: Write the configuration of the atom first, then remove the 4s electrons before any 3d electrons when the ion forms.
- A family of similar metals: Compare the transition metals with calcium, the s-block metal just before them, and notice how little their radii and ionisation energies change from Ti to Cu.
- Definition: stable ion with an incomplete d subshell.
- Ions: remove 4s before 3d.
- Exceptions: Cr 3d54s1, Cu 3d104s1.
- Properties: variable oxidation states, catalysts, coloured, complexes.
One picture every idea returns to
A transition element is a d-block element that forms one or more stable ions with an incomplete d subshell. Scandium (only Sc3+, 3d0) and zinc (only Zn2+, 3d10) are d-block elements but not transition elements. Across Ti to Cu, electrons enter the inner 3d subshell, so the extra nuclear charge is largely shielded: atomic radii and first ionisation energies stay very similar. When ions form, the 4s electrons are lost first. Chromium (3d54s1) and copper (3d104s1) are exceptions to the filling order. Transition elements show variable oxidation states, act as catalysts, form coloured compounds and form complex ions.
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, An incomplete d subshell.. Titanium to copper sit in the middle of period 4, filling the 3d subshell. 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: Configurations and the definition | Write the configuration of the atom first, then remove the 4s electrons before any 3d electrons when the ion forms. Project tab 1 of the lab (Transition elements lab, configurations and the definition) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: A family of similar metals | Compare the transition metals with calcium, the s-block metal just before them, and notice how little their radii and ionisation energies change from Ti to Cu. Project tab 1 of the lab (Transition elements lab, configurations and the definition) and let a student drive it while the class predicts. | 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, 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 A family of similar metals, 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 |
|---|---|
| When forming ions, remove the 4s electrons first: Fe 2+ is [Ar]3d 6, not [Ar]3d 4 4s 2. | Chromium is 3d 5 4s 1 and copper 3d 10 4s 1. Zinc is in the d block but is not a transition element, because Zn 2+ has a full 3d subshell; scandium is excluded because Sc 3+ has no d electrons. |
Physical properties of transition elements: worksheet
6 questions, 16 marks. Written in the style of the papers; no past paper question is reproduced.
Write full electronic configurations for (a) V, (b) V3+, (c) Co2+.
Scandium and zinc are d-block elements. Explain why neither is a transition element, while copper is.
Explain why the copper atom has the configuration [Ar]3d104s1 rather than [Ar]3d94s2.
The first ionisation energies of Ti to Cu lie between 650 and 760 kJ mol−1. Explain why they are so similar.
How many unpaired electrons are present in (a) Fe2+ and (b) Cr3+? Show your reasoning.
State three chemical properties typical of transition elements, giving an example of each.
Answer key and marking notes
- (a) 1s22s22p63s23p63d34s2.
- (b) 1s22s22p63s23p63d2 (4s electrons removed first, then one 3d).
- (c) 1s22s22p63s23p63d7.
- A transition element forms one or more stable ions with an incomplete d subshell.
- Sc forms only Sc3+, [Ar], with no d electrons; Zn forms only Zn2+, [Ar]3d10, a full d subshell.
- Cu forms Cu2+, [Ar]3d9, an incomplete d subshell, so copper is a transition element.
- The 3d and 4s energies are very close.
- A completely filled 3d subshell is especially stable, so one 4s electron occupies 3d instead.
- Across the series the nuclear charge increases by one each time.
- The extra electron goes into the inner 3d subshell, which shields the outer 4s electrons.
- So the attraction for the 4s electron (the one removed) increases only slightly, and the ionisation energies change little.
- (a) Fe2+ is 3d6: one pair plus four single electrons, so 4 unpaired.
- (b) Cr3+ is 3d3: three single electrons in separate orbitals, so 3 unpaired.
- Variable oxidation states: iron forms Fe2+ and Fe3+; manganese forms +2 to +7.
- Catalytic activity: iron in the Haber process; V2O5 in the Contact process.
- Coloured compounds and complex ions: [Cu(H2O)6]2+ is pale blue.
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 is the Cambridge definition of a transition element?
- Aa d-block element that forms one or more stable ions with an incomplete d subshell
- Bany element in the d block of the Periodic Table
- Ca d-block element whose atom has a partially filled d subshell
- Da metal that forms coloured compounds in all of its oxidation states
Why is zinc NOT classed as a transition element?
- Aits only ion, Zn2+, has the configuration [Ar] 3d10, a full d subshell
- Bit is not in the d block of the Periodic Table
- Cits atom has no 3d electrons
- Dit does not form any ions in aqueous solution
What is the electron configuration of a chromium atom (Z = 24)?
- A[Ar] 3d5 4s1
- B[Ar] 3d4 4s2
- C[Ar] 3d6
- D[Ar] 3d5 4s2
What is the electron configuration of the Fe3+ ion? (Fe is [Ar] 3d6 4s2)
- A[Ar] 3d5
- B[Ar] 3d3 4s2
- C[Ar] 3d6
- D[Ar] 3d4 4s1
Which statement is NOT a characteristic property of the transition elements?
- Athey have low densities and low melting points, like the Group 1 metals
- Bthey show variable oxidation states in their compounds
- Cthey and their compounds often act as catalysts
- Dthey form complex ions and coloured compounds
Which ion has an incomplete d subshell?
- ACu2+, [Ar] 3d9
- BCu+, [Ar] 3d10
- CSc3+, [Ar]
- DZn2+, [Ar] 3d10
How many unpaired electrons are there in a gaseous Co2+ ion? (Co is [Ar] 3d7 4s2)
- A3
- B5
- C7
- D1
Manganese ([Ar] 3d5 4s2) shows oxidation states from +2 to +7. Which statement best explains this?
- Athe 3d and 4s electrons are close in energy, so different numbers of them can be lost or used in bonding, up to all seven
- Bmanganese has seven electrons in its 3d subshell, which can be lost one at a time
- Cmanganese can also lose electrons from its 4p subshell
- Dmanganese ions gain extra electrons from ligands, raising the oxidation state
Quiz key
A transition element is a d-block element that forms one or more stable ions with an incomplete d subshell, so titanium to copper qualify in Period 4. Simply being in the d block is not enough: scandium and zinc are d-block elements but are not transition elements. A definition based on the atom fails too, because the scandium atom ([Ar] 3d1 4s2) has a partly filled d subshell, yet its only ion Sc3+ has none. Colour is a typical property, not the definition, and some oxidation states (for example Cu+, 3d10) are colourless.
Zinc is [Ar] 3d10 4s2 and forms only Zn2+, [Ar] 3d10. Neither the atom nor the ion has an incomplete d subshell, so zinc fails the definition. Zinc is in the d block (its last electrons in the build-up go into 3d), so that option is wrong. The zinc atom has ten 3d electrons, not none. Zinc readily forms Zn2+(aq), for example in zinc sulfate solution.
Chromium is [Ar] 3d5 4s1: one electron sits in each of the five 3d orbitals and one in 4s. Spreading the electrons out like this reduces repulsion and gives a stable half-filled 3d subshell. [Ar] 3d4 4s2 is what the simple filling rule predicts, and it is the classic error. [Ar] 3d6 empties 4s completely, which does not happen for the atom. [Ar] 3d5 4s2 has 25 electrons, so it is manganese, not chromium. Copper, [Ar] 3d10 4s1, is the other exception.
The 4s electrons are lost first, then 3d. Fe [Ar] 3d6 4s2 loses two 4s electrons and one 3d electron to give Fe3+ [Ar] 3d5. [Ar] 3d3 4s2 removes all three from 3d, which is the classic error: 4s fills first but also empties first. [Ar] 3d6 is Fe2+, which has lost only two electrons. [Ar] 3d4 4s1 has lost one 4s and two 3d electrons, again not the 4s-first order.
Transition elements are dense metals with high melting points, because both 3d and 4s electrons are delocalised in metallic bonding and the ions are small. The low density, low melting point option describes Group 1, so it is the statement that is NOT characteristic. Variable oxidation states (3d and 4s are close in energy), catalytic activity (for example Fe in the Haber process, V2O5 in the Contact process) and the formation of complexes and coloured compounds are all genuine characteristic properties.
Copper loses its 4s electron to form Cu+ ([Ar] 3d10), then one 3d electron to form Cu2+ ([Ar] 3d9). Only Cu2+ has a partly filled d subshell, which is why copper counts as a transition element and why copper(II) compounds are coloured. Cu+ and Zn2+ have full 3d subshells, and Sc3+ has no 3d electrons at all, so none of those has an incomplete d subshell.
Co2+ is [Ar] 3d7. Seven electrons in five d orbitals: one in each orbital (5), then two more pair up, leaving 3 unpaired. 5 comes from removing the two electrons from 3d instead of 4s ([Ar] 3d5 4s2, five unpaired). 7 counts every 3d electron as unpaired, ignoring that only five orbitals are available. 1 pairs electrons before every orbital is singly occupied, which breaks Hund's rule.
The 3d and 4s subshells are close in energy, so there is no large jump in successive ionisation energies until all the 4s and 3d electrons have gone. Manganese can therefore use 2, 3, 4, 6 or all 7 of them, as in MnO4− (+7). Manganese has five 3d electrons, not seven; the seven comes from 3d5 + 4s2. The 4p subshell is empty in manganese. Gaining electrons from ligands (dative bonds) does not raise an oxidation state; oxidation means losing electrons.
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.