Egypt Secondary 3 Chemistry, Week 1: The first series in use: scandium to manganese

The d block and the first series in use

Week 1 · Chapter 1 Transition Elements (A): chapter opener and objectives, the d block and the four transition series, the first series Sc to Zn and the uses of each element (light, descriptive week) · 3 lessons

The first series in use: scandium to manganese

Chemistry Sec 3 Term 1, Chapter 1: pp. 1–8

GoalLink each of scandium, titanium, vanadium, chromium and manganese to a useful property and a use, with one compound each.

New words

alloy · a metal mixed with small amounts of other elements to improve its propertiesoxide layer · a thin film of metal oxide on a metal surface; if it is tight it protects the metal underneathoxidising agent · a substance that takes electrons from another substance in a reaction

Explanation

In the Earth’s crust the first series accounts for about 6 % of the mass, and iron alone for about 5 %. All ten are hard metals with high melting points, but each has a special property that decides its use. Scandium: a little in aluminium gives a light, very hard alloy for aircraft parts and sports equipment; it is also added to some lamps to give light close to daylight. Titanium: as strong as steel but lighter, and inert in the body, so it is used for aircraft parts, joints and dental implants; tiny particles of its oxide TiO₂ in sun creams block UV light. Vanadium: a little in steel gives a hard steel that resists corrosion, used for springs; V₂O₅ colours glass and ceramics and is a catalyst. Chromium: an active metal, yet a thin tight oxide layer protects it, so it is used for plating and in leather tanning; Cr₂O₃ is a green pigment and K₂Cr₂O₇ is an oxidising agent. Manganese: brittle by itself, so it is used in alloys (ferromanganese for rails, aluminium–manganese for drink cans) or as compounds such as MnO₂ and KMnO₄, both oxidising agents.

Element	Property that matters	Use
scandium	very hard alloy with aluminium, light	aircraft parts, lamps
titanium	strong, light, inert	aircraft parts, implants, TiO₂ in sun creams
vanadium	hardens steel, resists corrosion	springs, V₂O₅ as colour and catalyst
chromium	tight oxide layer	plating, tanning, Cr₂O₃ pigment
manganese	alloys harder than steel; brittle alone	rails, drink cans, MnO₂, KMnO₄

Worked examples

Choose the metal. A designer needs a metal that is as strong as steel but lighter, and that is inert in the body. The first property suits aircraft parts and the second suits an implant: both point to titanium.

Why is manganese never used as a pure metal? It is brittle, so it breaks instead of bending. Mixed with iron it makes ferromanganese, harder than ordinary steel and used for rails; mixed with aluminium it gives an alloy that resists corrosion, used for drink cans.

A chromium-plated tap stays bright even though chromium is an active metal. Chromium does react with oxygen at once, but the oxide forms a thin tight layer that covers the surface without gaps (the oxide takes up more room than the metal atoms it came from). Oxygen cannot reach the metal below, so the reaction stops after the first thin layer.

Class activity

A metal hunt at home, with a grown-up. Find three metal objects, for example a spring, a drink can, a tap or a bicycle part. For each, write which property of its metal matters most: hardness, low mass, resistance to corrosion or shine. Read any label on the object and note which metals it names. Do not scratch, cut or heat anything.

Practice

Match each use to one of the elements V, Ti, Mn: (a) springs of corrosion-resistant steel, (b) drink cans, (c) body implants.

Which element of this lesson is an active metal but resists corrosion, and why?

Give a use of each compound: (a) TiO₂, (b) V₂O₅, (c) K₂Cr₂O₇.

Scandium is found only in tiny amounts spread thinly through the crust. Why is it still useful to add a little of it to aluminium?