Transition Metals

The metals you meet most often in everyday life — iron in steel, copper in wiring, the chromium on a tap — are not the dramatic, dangerously reactive alkali metals of Group 1. They belong to a large block in the centre of the periodic table called the transition metals, and they have exactly the properties that make a good structural and engineering material: they are hard, strong, dense and far less reactive than Group 1. This lesson, part of Topic C2 of OCR Gateway Science A, sets out the characteristic properties of the transition metals, contrasts them with the alkali metals, and looks at their special features — coloured compounds, catalytic activity and variable charges.

By the end of this lesson you should be able to locate the transition metals on the periodic table, compare their properties with the Group 1 metals, and describe their characteristic properties: forming coloured compounds, acting as catalysts, and forming ions with variable charges.

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Where the Transition Metals Are

The transition metals form the large central block of the periodic table, positioned between Group 2 and Group 3. They include many of the most familiar metals — iron (Fe), copper (Cu), zinc (Zn), nickel (Ni), chromium (Cr) and others. Because they are all metals, they share the general metallic properties (they conduct electricity and heat, and are shiny when freshly cut), but they also have a distinctive set of properties of their own that mark them out from the Group 1 metals.

flowchart LR
  A["Group 1<br/>alkali metals"] --> B["Transition metals<br/>(central block)"]
  B --> C["Group 7<br/>halogens"]
  B --> D["Hard, strong, dense"]
  B --> E["High melting points"]
  B --> F["Much less reactive"]

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Transition Metals Compared with Group 1

The clearest way to understand the transition metals is to contrast them directly with the alkali metals, which sit just to their left.

Property	Group 1 (alkali metals)	Transition metals
Hardness	Soft (cut with a knife)	Hard and tough
Strength	Weak	Strong
Density	Low (some float on water)	High (dense)
Melting point	Low	High
Reactivity	Very reactive (react fast with water and oxygen)	Much less reactive (react slowly or not at all)

So the transition metals are harder, stronger, denser and have much higher melting points than the Group 1 metals, and they are far less reactive. For example, iron reacts only slowly with oxygen and water (it rusts over days and weeks), and copper is so unreactive it can be used for water pipes and roofing — a world away from sodium, which fizzes violently on water within seconds. This low reactivity, combined with their strength, is exactly why transition metals are used for tools, machinery, construction and wiring.

Exam Tip: A reliable comparison sentence: transition metals are harder, stronger, denser, have higher melting points and are much less reactive than the Group 1 metals. Iron and copper react slowly (or barely) with water, unlike the alkali metals.

What "Much Less Reactive" Means in Practice

It is worth being concrete about the reactivity difference, because exam questions often test it through observations. A Group 1 metal such as sodium, dropped into water, reacts immediately and violently — it fizzes, melts into a ball, skates across the surface and may ignite, all within a few seconds. A transition metal such as iron does almost nothing when placed in cold water; it reacts only very slowly, needing both air and water over days and weeks to form rust. Copper is even less reactive: it does not react with water at all under normal conditions, which is precisely why copper has been used for water pipes and roofing for centuries.

This contrast matters because reactivity decides what a metal can be used for. You would never build anything from sodium — it would react with the moisture in the air. But the low reactivity of transition metals, combined with their strength and hardness, makes them ideal for structures, machinery, tools and pipework that must last. So the physical properties and the low reactivity work together to make transition metals the practical, everyday metals.

Exam Tip: If a question shows a transition metal reacting slowly or not at all with water while a Group 1 metal reacts vigorously, the point being tested is that transition metals are much less reactive — and that this low reactivity (plus strength) is why they are used as structural metals.

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Characteristic Property 1: Coloured Compounds

A striking feature of the transition metals is that they form coloured compounds, whereas Group 1 (and many other) compounds are white and dissolve to give colourless solutions. The colour depends on the metal and on its charge.

Transition-metal ion	Colour of compound / solution
Copper(II), $\text{Cu}^{2+}$Cu2+	blue / blue-green
Iron(II), $\text{Fe}^{2+}$Fe2+	pale green
Iron(III), $\text{Fe}^{3+}$Fe3+	orange-brown
Chromium(III), $\text{Cr}^{3+}$Cr3+	green

These colours are genuinely useful: the blue of copper sulfate, the green of iron(II) compounds and the orange-brown of iron(III) (rust) are all recognisable, and the colour can even tell a chemist which ion is present and what its charge is. By contrast, sodium, potassium and calcium compounds are white and their solutions colourless.

Exam Tip: Forming coloured compounds is a characteristic property of transition metals — it is a quick way to tell a transition-metal compound from a Group 1 one (which is white/colourless). Learn copper = blue, iron(II) = pale green, iron(III) = orange-brown.

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Characteristic Property 2: Catalysts

Transition metals (and their compounds) are widely used as catalysts — substances that speed up a reaction without being used up. Their catalytic ability is one of the main reasons they are so important in industry.

Key examples to remember:

• Iron is the catalyst in the Haber process, which makes ammonia from nitrogen and hydrogen.
• Nickel is used as a catalyst in the hydrogenation of vegetable oils (turning unsaturated oils into solid fats, e.g. for margarine).
• Platinum (and other transition metals) are used in catalytic converters in car exhausts.

Because a catalyst is not consumed, a small amount can be used over and over, which makes transition-metal catalysts very cost-effective in large-scale manufacturing.

Exam Tip: Learn two named catalysts: iron in the Haber process and nickel in hydrogenation (of oils). Acting as a catalyst is a characteristic property of the transition metals — Group 1 metals do not do this.

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Characteristic Property 3: Variable Charges (Oxidation States)

Group 1 metals always form +1 ions and Group 2 always +2, but a transition metal can form ions with more than one charge — it has variable oxidation states. This is why we use Roman numerals in the names of their compounds, to show which charge is present.

• Iron forms $\text{Fe}^{2+}$Fe2+ (iron(II)) and $\text{Fe}^{3+}$Fe3+ (iron(III)). Iron(II) compounds are pale green; iron(III) compounds are orange-brown.
• Copper is usually $\text{Cu}^{2+}$Cu2+ (copper(II)) but can also form $\text{Cu}^+$Cu+ (copper(I)).