Ch 4 · Transition Elements · IGCSE Chemistry 0620
Topic 4 of 5 in The Periodic Table — IGCSE Chemistry 0620 — 38 lessons.
Introduction
Iron in bridges, copper in wiring, titanium in aircraft, platinum in catalytic converters: the transition elements are the metals that industry actually uses. They sit in the block between Groups II and III and behave very differently from the soft, violently reactive metals of Group I. This lesson lists their characteristic properties, explains why iron needs a Roman numeral in its compound names, and sets out the comparison with Group I that examiners like to ask for.
Key ideas — Characteristic properties of the transition elements
The transition elements are the metals in the central block of the Periodic Table, including titanium, chromium, manganese, iron, cobalt, nickel, copper and zinc, with silver, platinum and gold further down. They are typical metals, malleable, shiny and good conductors of heat and electricity, and in addition they share four characteristic properties:
🧑🏫 Teacher's explanation
Imagine you are comparing a group of lightweight, hyper-reactive gymnasts (Group I metals like Sodium) to a group of heavy, incredibly strong weightlifters (Transition Metals). The gymnasts are light and react violently with just a drop of water, but the weightlifters are dense, tough, and can handle much more stress before they change their state or react.
📖 Definitions
🔍 Worked example — Easy
Calculate the density of a block of copper with a mass of 53.5 g and a volume of 6.0 cm^3.
🔍 Worked example — Standard
Identify the oxidation state of Iron in FeCl_2 and FeCl_3.
🔍 Worked example — Exam-style
A student observes that CuSO_4(aq) is blue, while NaCl(aq) is colorless. Explain this difference based on the properties of transition elements.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Name the catalyst used in the Haber process for the production of ammonia. [1] (b) State one difference between the reactivity of transition metals and Group I metals with water. [1] [2 marks]
Key ideas — Variable oxidation numbers
🧑🏫 Teacher's explanation
Imagine you have a collection of Lego bricks. Most bricks (like Group I metals) are 'single-use'—they only have one way to snap onto another piece. Transition metals, however, are like 'multi-tool' bricks; they can change their shape or how they connect depending on the situation. This 'flexibility' is what we call variable oxidation numbers.
📖 Definitions
🔍 Worked example — Easy
Identify the oxidation number of Iron in the compound FeCl_2 and FeCl_3 using the Roman numeral convention.
🔍 Worked example — Standard
A reaction involves the oxidation of iron(II) ions to iron(III) ions. Write the half-equation for this process.
🔍 Worked example — Exam-style
Calculate the mass of Fe_2O_3 produced if 2.0 moles of Fe^3+ ions react completely with oxygen ions to form the oxide. (Ar: Fe = 56, O = 16)
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State the color of the precipitate formed when sodium hydroxide is added to the iron(II) solution. [1] (b) Explain why transition metals like iron are often used as catalysts in industrial processes. [2] [3 marks]
Key ideas — Comparing transition elements with Group I metals
The similarities are that both are metals: conductors, malleable, and both form positive ions and basic oxides. The differences are what make the transition elements useful as structural materials, while Group I metals are useful mainly as their compounds.
🧑🏫 Teacher's explanation
Think of Group I metals like soft, reactive butter. They are light, they melt easily, and they react violently if you even look at them wrong. They are 'unstable' in their environment. Transition elements, however, are like heavy, tough steel. They are dense, hard, and much more 'chill' when meeting water or air.
📖 Definitions
🔍 Worked example — Easy
State two physical properties that distinguish transition elements from Group I metals.
🔍 Worked example — Standard
An unknown metal M reacts very slowly with water and forms a blue coloured solution when reacted with acid. Is M likely a Group I metal or a transition element? Justify your answer.
🔍 Worked example — Exam-style
Iron can form Fe^2+ and Fe^3+ ions. Calculate the mass of 0.5 moles of Fe^2+ ions. (Ar of Fe = 56).
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
Worked example
Question. The table gives some data for two metals.
🔍 Worked example — Easy
Metal X has a melting point of 961^° C and a density of 7.87 g/cm^3. Metal Y has a melting point of 98^° C and a density of 0.97 g/cm^3. Which is a transition element? Give two reasons.
🔍 Worked example — Standard
Explain why transition metals are often used as catalysts in industrial processes.
🔍 Worked example — Exam-style
Iron can form FeCl_2 and FeCl_3. Name the ions present in each and explain why iron can form both.
⚠️ Common errors
Common mistakes
Practice
Answers High density [B1]; high melting point [B1]; form coloured compounds [B1]; act as catalysts [B1]. Any correct pair, for example iron in the Haber process, vanadium(V) oxide in the Contact process, nickel in hydrogenation of oils, or platinum in catalytic converters [B2]. Potassium has a lower density and a lower melting point [B1]; it is soft and far more reactive, reacting violently with water [B1]; its compounds are white or colourless whereas copper compounds are coloured [B1]. FeSO_4 [B1]; Fe_2(SO_4)_3 [B1]; the Roman numeral gives the oxidation number (charge) of the iron ion, +2 or +3 [B1].