4.1.3.1Comparison with Group 1 elements
Chemistry only — not assessed in Combined Science: Trilogy.
The transition elements are metals with similar properties which are different from those of the elements in Group 1. They occupy the central block of the periodic table, between Group 2 and Group 3.
They are still metals, so they still form positive ions and conduct heat and electricity. What is being tested here is the contrast with the alkali metals, which behave very unlike a metal in everyday use — soft enough to cut with a knife, and violently reactive with water.
You should be able to describe the difference compared with Group 1 in melting points, densities, strength, hardness and reactivity with oxygen, water and halogens.
You should also be able to exemplify these general properties by reference to Cr, Mn, Fe, Co, Ni and Cu — chromium, manganese, iron, cobalt, nickel and copper. Naming one of those six turns a general statement into an answer that scores: not "transition metals are less reactive", but "copper does not react with water, whereas potassium reacts violently with it".
Common mistake
Less reactive does not mean unreactive. Iron reacts with oxygen and water — that is what rusting is — just far more slowly than a Group 1 metal does. Say slower or less vigorous, not "does not react", unless you mean a metal such as copper with water.
- Transition elements
- the metals occupying the central block of the periodic table between Group 2 and Group 3, with properties different from those of Group 1
4.1.3.2Typical properties
Chemistry only — not assessed in Combined Science: Trilogy.
Many transition elements have ions with different charges, form coloured compounds and are useful as catalysts. Those three are the typical properties, and each one separates the transition metals from Group 1, where the ion is always 1+, the compounds are white and the metals are not used as catalysts.
- Transition element
- A metal from the central block of the periodic table, with properties different from those of Group 1.
- Catalyst
- A substance that speeds up a reaction without being used up in the reaction.
You should be able to exemplify these general properties by reference to compounds of Cr, Mn, Fe, Co, Ni and Cu. As with the previous section, name the compound — copper(II) sulfate solution is blue; iron(II) sulfate solution is pale green — rather than only stating that transition metal compounds are coloured.
The Roman numeral in a name such as iron(III) chloride exists precisely because of the first property: it says which of the possible charges the ion carries. Iron(II) chloride is FeCl₂ and iron(III) chloride is FeCl₃, and the compounds are different colours.
Worked example
A green solid dissolves to give a pale green solution, and the solid acts as a catalyst in a different reaction. Suggest which element it contains, and justify each part of your answer.
- A coloured compound points to a transition element rather than a Group 1 metal, whose compounds are white and give colourless solutions.
- Being useful as a catalyst is a second typical property of the transition elements, so both clues agree.
- Pale green in solution is characteristic of iron(II) compounds.
- Name the element and the evidence for it, not just the group.
Answer: Iron. The colour shows it is a transition element compound rather than a Group 1 compound, the pale green points specifically to iron(II), and transition elements are useful as catalysts.
Before you practise
- This sub-topic is chemistry only — it is not assessed in Combined Science: Trilogy.
- The transition elements are metals with similar properties, different from those of Group 1.
- Compared with Group 1 they have higher melting points, higher densities, and are stronger and harder.
- They are much less reactive with oxygen, water and the halogens than the alkali metals are.
- Many have ions with different charges — Fe²⁺ and Fe³⁺, Cu⁺ and Cu²⁺.
- Many form coloured compounds, and many are useful as catalysts.
- Use Cr, Mn, Fe, Co, Ni and Cu, and their compounds, as your named examples.