AQA GCSE Chemistry 8462: Properties of transition metals – Study Guide

This study guide teaches section 4.1.3 Properties of transition metals of the AQA GCSE Chemistry (8462) specification, for teaching from September 2016 with exams from June 2018 (version 1.1). It covers both statements in that section: 4.1.3.1 Comparison with Group 1 elements and 4.1.3.2 Typical properties. The section sits in Topic 1, Atomic structure and the periodic table, which is assessed on Paper 1 (1 hour 45 minutes, 100 marks, Foundation and Higher tier). Nothing in 4.1.3 is Higher tier only, so everything here is for both tiers, and the specification lists no required practical for this section.

The specification marks 4.1.3 “chemistry only”: it is not in Combined Science. The whole topic is covered in the Atomic structure and the periodic table guide, the atomic structure revision notes and the atomic structure practice questions; this page goes deeper on transition metals only.

What this section covers

Spec	What you must be able to do	Tier
4.1.3.1	Describe how transition metals differ from Group 1 in melting points, densities, strength, hardness, and reactivity with oxygen, water and halogens	Foundation and Higher
4.1.3.1	Give examples of these general properties using Cr, Mn, Fe, Co, Ni, Cu	Foundation and Higher
4.1.3.2	State that many transition elements have ions with different charges, form coloured compounds and are useful as catalysts	Foundation and Higher
4.1.3.2	Give examples of these properties using compounds of Cr, Mn, Fe, Co, Ni, Cu	Foundation and Higher

The six named elements are the ones to learn: chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu). They sit next to each other in the central block of the periodic table, between Group 2 and Group 3. You must describe how they behave and back each point with one of these six. Two ideas run through the section: the transition metals have similar properties to each other, and those properties are different from Group 1 (lithium, sodium, potassium and the rest). Both groups are metals that conduct electricity and heat; the differences lie in the properties below.

4.1.3.1 Comparison with Group 1

Physical properties

Property	Group 1 metals	Transition metals
Melting point	Low (all below 200 °C)	High (all six named metals above 1000 °C)
Density	Low (lithium, sodium and potassium float on water)	High (around 7–9 g/cm³)
Strength	Weak	Strong
Hardness	Soft; can be cut with a knife	Hard

Data for the named elements (values from the Royal Society of Chemistry periodic table, melting points rounded to the nearest degree):

Element	Melting point / °C	Density / g/cm³
Lithium (Li)	181	0.53
Sodium (Na)	98	0.97
Potassium (K)	64	0.89
Chromium (Cr)	1907	7.15
Manganese (Mn)	1246	7.3
Iron (Fe)	1538	7.87
Cobalt (Co)	1495	8.86
Nickel (Ni)	1455	8.90
Copper (Cu)	1085	8.96

You will not be asked to recall these numbers, but you may be given data like this to describe or compare. Strength and hardness are why iron (as steel) is used for structures and tools; sodium is soft enough to cut with a knife and reacts with water, so it could never be used that way.

Worked example 1: describing data

Question. Use the table to compare iron with sodium. Refer to melting point and density. [4]

Step 1 – state the direction for melting point. Iron has a much higher melting point than sodium.

Step 2 – quote figures to back it up. Iron melts at 1538 °C and sodium at 98 °C, a difference of 1538 − 98 = 1440 °C.

Step 3 – state the direction for density. Iron is much denser than sodium.

Step 4 – quote figures. 7.87 ÷ 0.97 = 8.1, so iron is about 8 times as dense as sodium. Sodium’s density is below 1 g/cm³, so it floats on water. Iron sinks.

Pattern: a comparison plus supporting data for each property. Use comparative words: higher, lower, denser, harder.

Reactivity with oxygen, water and halogens

Transition metals are much less reactive than Group 1 metals. The specification names three reactants. Learn a Group 1 example and a transition metal example for each.

With oxygen

• Group 1: freshly cut sodium or potassium tarnishes within seconds in air as an oxide forms. They are stored under oil. Lithium burns in oxygen: 4Li + O₂ → 2Li₂O.
• Transition metals: react slowly or only when heated. Copper heated in air forms a black coating of copper(II) oxide: 2Cu + O₂ → 2CuO. Iron rusts slowly at room temperature, but only when both air and water are present. Iron wool burns when heated in oxygen.

With water

• Group 1: react with cold water, fizzing and releasing hydrogen, to form an alkaline hydroxide solution: 2Na + 2H₂O → 2NaOH + H₂. Potassium reacts so fast that the hydrogen ignites.
• Transition metals: copper does not react with water. Iron reacts with cold water only very slowly, and only as part of rusting with oxygen. This is why copper is used for water pipes.

With halogens

• Group 1: react vigorously with chlorine. Sodium burns with a bright yellow flame to form white sodium chloride: 2Na + Cl₂ → 2NaCl.
• Transition metals: react, but less vigorously, and usually need heating. Hot iron wool glows in chlorine to form brown iron(III) chloride: 2Fe + 3Cl₂ → 2FeCl₃. Heated copper reacts with chlorine to form copper(II) chloride: Cu + Cl₂ → CuCl₂.

The reactions of the first three alkali metals with oxygen, chlorine and water are covered in more detail in section 4.1.2.5, in the topic study guide.

Worked example 2: a six-mark comparison

Question. Compare the properties of potassium and nickel. [6]

A strong answer makes paired comparisons, one property at a time:

1. Nickel has a much higher melting point than potassium (potassium melts at a low temperature; nickel needs well over 1000 °C).
2. Nickel is much denser; potassium floats on water.
3. Nickel is hard and strong; potassium is soft and can be cut with a knife.
4. Potassium reacts vigorously with cold water, releasing hydrogen that ignites. Nickel does not react with cold water in this way.
5. Potassium tarnishes rapidly in air; nickel does not.
6. Potassium reacts vigorously with chlorine; nickel reacts far less vigorously.

Each point names both metals or uses a comparative word. “Nickel is hard” alone does not compare.

4.1.3.2 Typical properties of transition metals

The specification gives three typical properties. Many (not necessarily all) transition elements:

1. have ions with different charges
2. form coloured compounds
3. are useful as catalysts.

You must give examples using compounds of Cr, Mn, Fe, Co, Ni and Cu.

Ions with different charges

A Group 1 metal always forms a 1+ ion (Na⁺, K⁺). A transition metal can often form ions with more than one charge. The charge appears as a Roman numeral in the compound’s name.

Element	Ions	Example compounds
Iron	Fe²⁺ and Fe³⁺	iron(II) sulfate FeSO₄; iron(III) chloride FeCl₃
Copper	Cu⁺ and Cu²⁺	copper(I) oxide Cu₂O; copper(II) oxide CuO
Chromium	Cr²⁺ and Cr³⁺	chromium(III) oxide Cr₂O₃
Cobalt	Co²⁺ and Co³⁺	cobalt(II) chloride CoCl₂

Manganese also shows different charges: it is Mn²⁺ in manganese(II) compounds, and manganese(IV) oxide is MnO₂.

Worked example 3: writing formulae from Roman numerals

Question. Write the formulae of (a) iron(II) chloride and (b) iron(III) oxide. [2]

(a) Iron(II) means Fe²⁺. Chloride is Cl⁻. Two Cl⁻ balance one Fe²⁺. Formula: FeCl₂.

(b) Iron(III) means Fe³⁺. Oxide is O²⁻. Find the lowest common multiple of 3 and 2, which is 6. Two Fe³⁺ give 6+, three O²⁻ give 6−. Formula: Fe₂O₃.

Check: total positive charge must equal total negative charge. In Fe₂O₃, 2 × 3 = 6 and 3 × 2 = 6.

Coloured compounds

Compounds of Group 1 metals are white solids that dissolve to give colourless solutions (sodium chloride, potassium sulfate). Transition metal compounds are usually coloured. Good examples:

Element	Compound	Colour
Copper	copper(II) sulfate (hydrated crystals or solution)	blue
Copper	copper(II) carbonate	green
Iron	iron(II) compounds	pale green
Iron	iron(III) compounds	orange-brown
Chromium	chromium(III) oxide	green
Chromium	potassium dichromate	orange
Manganese	potassium manganate(VII)	purple
Cobalt	hydrated cobalt(II) chloride	pink
Nickel	nickel(II) sulfate	blue-green

The colour often depends on the ion’s charge. Iron(II) and iron(III) compounds are different colours. This is used in chemical analysis (section 4.8.3.2): adding sodium hydroxide solution gives a blue precipitate with copper(II) ions, a green precipitate with iron(II) ions and a brown precipitate with iron(III) ions. For example:

CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄
         blue precipitate: Cu(OH)₂

See the Chemical analysis study guide for the full set of ion tests.

Catalysts

A catalyst changes the rate of a reaction but is not used up. Many transition metals and their compounds are useful catalysts. Two examples you should know:

• Iron is the catalyst in the Haber process, which makes ammonia: N₂ + 3H₂ ⇌ 2NH₃.
• Manganese(IV) oxide speeds up the decomposition of hydrogen peroxide: 2H₂O₂ → 2H₂O + O₂.

Other examples you may meet: nickel is used to add hydrogen to vegetable oils, and copper(II) sulfate speeds up the reaction between zinc and dilute acid. The specification says you do not need to know catalyst names other than those it specifies, so iron in the Haber process is the one to have ready.

You can spot a catalyst in an equation or method because it is not in the chemical equation: it is written over the arrow or listed as a condition. In experiments, it speeds up the reaction and the same mass is left at the end.

Worked example 4: identifying a catalyst from data

Question. A student adds 0.5 g of three different metal oxides, A, B and C, to separate 25 cm³ portions of the same hydrogen peroxide solution. She measures the volume of oxygen made in 50 s.

Oxide	Volume of oxygen in 50 s / cm³	Mass of solid at end / g
none	6	–
A	48	0.5
B	30	0.5
C	6	0.5

(a) Which oxides act as catalysts? (b) Calculate the mean rate of oxygen production with oxide A. [4]

(a) A and B. Each gives more oxygen in 50 s than with no oxide, so the reaction is faster. Each mass is unchanged, so the solid is not used up. Oxide C gives the same volume as no oxide, so it is not a catalyst for this reaction.

(b) Mean rate = volume ÷ time = 48 ÷ 50 = 0.96 cm³/s.

The mass check matters. A solid that speeds up a reaction but gets used up is a reactant, not a catalyst. Rates of reaction and how catalysts work are in Topic 6: see the rate and extent of chemical change study guide.

Common errors

• Writing “transition metals are more reactive”. They are less reactive than Group 1.
• Saying “transition metals are heavier”. Write denser: a large lump of sodium can weigh more than a small iron nail.
• Describing only one metal when the question says “compare”.
• Giving an example from outside the list when asked about Cr, Mn, Fe, Co, Ni or Cu.
• Naming iron(II) and iron(III) compounds without the Roman numeral, or swapping their colours (iron(II) green, iron(III) orange-brown).
• Writing the catalyst into the equation as a reactant.
• Saying all transition metals form coloured compounds or that all are catalysts. The specification says many.

Next steps

Use the revision notes, then the practice questions. The AQA GCSE Chemistry hub, the printable checklist and the free diagnostics show where else to work.

Official syllabus

AQA GCSE Chemistry (8462) specification, for teaching from September 2016, GCSE exams June 2018 onwards, version 1.1, published by AQA – section 4.1.3 Properties of transition metals (4.1.3.1 and 4.1.3.2).