🔩 Metals
Secondary School Chemistry • MalawiHub
1. Introduction
Metals are elements that generally have good electrical and thermal conductivity, are malleable and form positive ions by losing electrons.
Learning Objectives
- Describe physical properties of metals.
- Use the reactivity series.
- Explain reactions of metals.
- Describe extraction of metals.
- Explain corrosion and methods of prevention.
- Explain the importance of alloys.
2. Physical Properties
- Good conductors of electricity.
- Good conductors of heat.
- Malleable.
- Ductile.
- Usually shiny when polished.
- Usually strong and dense.
- Many have high melting points.
3. Reactivity Series
| More reactive |
|---|
| Potassium (K) |
| Sodium (Na) |
| Calcium (Ca) |
| Magnesium (Mg) |
| Aluminium (Al) |
| Carbon (C) |
| Zinc (Zn) |
| Iron (Fe) |
| Hydrogen (H) |
| Copper (Cu) |
| Silver (Ag) |
| Gold (Au) |
The higher a metal is in the series, the more readily it loses electrons and forms positive ions.
4. Metals and Oxygen
Many metals react with oxygen to form metal oxides.
Metal oxides are often basic, although some are amphoteric.
5. Metals and Water
Some reactive metals react with water to form metal hydroxides and hydrogen.
Less reactive metals may react only with steam or may not react with water under ordinary conditions.
6. Metals and Acids
Metals above hydrogen in the reactivity series can generally react with dilute acids to produce a salt and hydrogen gas.
7. Displacement Reactions
A more reactive metal can displace a less reactive metal from its compound.
Zinc is more reactive than copper, so it displaces copper.
8. Extraction of Metals
Metal extraction depends on the position of the metal in the reactivity series.
- Very reactive metals are commonly extracted by electrolysis.
- Moderately reactive metals can often be extracted by reduction of their oxides using carbon or carbon monoxide.
- Very unreactive metals may occur naturally.
Iron can be extracted from iron oxide by reduction using carbon monoxide in a blast furnace.
9. Corrosion and Rusting
Corrosion is the gradual destruction of a metal through chemical reactions with its environment.
Rusting is the corrosion of iron in the presence of oxygen and water.
Preventing corrosion
- Painting.
- Oiling or greasing.
- Galvanising.
- Electroplating.
- Using alloys.
10. Alloys
An alloy is a mixture containing a metal and one or more other elements.
| Alloy | Main components | Example use |
|---|---|---|
| Steel | Iron + carbon | Construction |
| Stainless steel | Iron + chromium and other elements | Cutlery |
| Brass | Copper + zinc | Fittings |
| Bronze | Copper + tin | Engineering/art |
11. MANEB Examination Focus
- Arrange metals according to reactivity.
- Predict displacement reactions.
- Write equations for metal reactions.
- Explain extraction methods.
- Explain rusting.
- State methods of preventing corrosion.
- Explain why alloys are useful.
Why can zinc displace copper from copper(II) sulfate solution?
Zinc is more reactive than copper, so zinc loses electrons more readily and displaces copper from its compound.
12. Practice Exercises
- State two physical properties of metals.
- Which is more reactive: zinc or copper?
- Write the equation for magnesium reacting with oxygen.
- What gas is produced when zinc reacts with dilute hydrochloric acid?
- Define an alloy.
- State three methods of preventing rusting.
- Why are very reactive metals extracted by electrolysis?
Answers
- Good electrical conductivity and malleability.
- Zinc.
- 2Mg + O₂ → 2MgO.
- Hydrogen.
- A mixture containing a metal and one or more other elements.
- Painting, oiling and galvanising.
- They are too reactive to be easily reduced using carbon.
13. Common Mistakes
- Do not confuse corrosion with only rusting; rusting specifically involves iron.
- Remember that a more reactive metal displaces a less reactive metal.
- Do not say all metals react with water in the same way.
14. Exam Tip
When predicting a displacement reaction, compare the two metals in the reactivity series first.