Cambridge IGCSE0620

Properties of metals

Chemistry 0620 Chapter Notes

What this chapter covers

Properties of metalsUses of metalsAlloys and their propertiesReactivity seriesCorrosion of metalsExtraction of metals
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In this chapter

  1. 1Typical Physical Properties of Metals
  2. 2Metallic Bonding: Explaining the Properties
  3. 3Key Chemical Properties of Metals
  4. 4Metals vs. Non-Metals and Exceptions

1. Typical Physical Properties of Metals

Metals share a set of characteristic physical properties that determine their uses. They are generally strong and resistant to breaking. They are shiny when polished (lustrous) and make a ringing sound when struck (sonorous). Most metals have high melting and boiling points, meaning they are solid at room temperature (the exception is mercury). They also tend to have a high density, which means they feel heavy for their size. Crucially, they are excellent conductors of both heat and electricity. Many metals are also malleable (can be hammered into shape) and ductile (can be drawn into wires).

Density = Mass / Volume

Key term

Malleable: The ability of a material, like a metal, to be hammered or pressed into different shapes without breaking or cracking.

Common pitfall

Confusing malleable and ductile. Remember: Malleable is for making sheets (like a mallet), Ductile is for drawing into wires (like a duck's long neck).

Fun fact

The sonorous property of metals is why bells are made from bronze, an alloy of copper and tin. The specific shape and alloy composition are tuned to produce a pleasant musical note.

Worked example 12 marks

A block of aluminium has a mass of 54.0 g and a volume of 20.0 cm³. Calculate its density in g/cm³.

  1. 1

    Step 1: State the formula for density. Density = Mass / Volume.

  2. 2

    Step 2: Substitute the given values into the formula. Density = 54.0 g / 20.0 cm³.

  3. 3

    Step 3: Calculate the result. Density = 2.7 g/cm³.

Worked example 22 marks

Suggest and explain two reasons why copper is used for electrical wiring.

  1. 1

    Reason 1: Copper is a very good conductor of electricity, which allows electric current to flow through it with minimal resistance or energy loss.

  2. 2

    Reason 2: Copper is ductile, which means it can be easily and efficiently drawn out into thin wires without breaking.

Recap

  • Metals are generally strong, dense, and have high melting points.
  • They are good conductors of heat and electricity.
  • Malleable means they can be hammered into shape; ductile means they can be drawn into wires.
  • Most metals are solid at room temperature, except for mercury.
  • Metals are sonorous (make a ringing sound) and lustrous (shiny when polished).

Quick check

  1. What is the term for the property that allows a metal to be drawn into a wire?1 mark
  2. Name the only metal that is a liquid at room temperature.1 mark

2. Metallic Bonding: Explaining the Properties

The unique properties of metals are explained by their internal structure, known as metallic bonding. In a metal, the atoms are arranged in a giant, regular lattice. Each atom loses its outer shell electrons, becoming a positive ion. These electrons are no longer tied to any single atom; instead, they form a 'sea' of delocalised electrons that are free to move throughout the entire structure. The metallic bond is the strong electrostatic force of attraction between the positive metal ions and the negative sea of delocalised electrons. This model perfectly explains why metals behave as they do.

Key term

Delocalised Electrons: Electrons in a metal that are not associated with any single atom and are free to move throughout the entire metallic lattice.

Examiner insight

Examiners award high marks for answers that explicitly link a metal's properties (like conductivity or malleability) to the movement of delocalised electrons within the giant metallic lattice.

Fun fact

The characteristic lustre (shininess) of metals is caused by the delocalised electrons. They absorb photons of light and immediately re-emit them, making the surface appear reflective.

Worked example 13 marks

Explain, in terms of structure and bonding, why a metal like silver is an excellent conductor of electricity.

  1. 1

    Step 1: Describe the structure. Silver has a giant metallic lattice structure consisting of positive silver ions (Ag⁺).

  2. 2

    Step 2: Identify the charge carriers. It is surrounded by a 'sea' of delocalised electrons.

  3. 3

    Step 3: Explain conduction. When a voltage is applied, these delocalised electrons are free to move through the lattice and carry charge, resulting in an electric current.

Worked example 23 marks

Explain why metals are typically malleable.

  1. 1

    Step 1: Refer to the structure. Metals consist of layers of positive ions in a sea of delocalised electrons.

  2. 2

    Step 2: Describe what happens under force. When a force is applied, the layers of positive ions can slide over one another.

  3. 3

    Step 3: Explain why it doesn't break. The delocalised electrons move with the ions, maintaining the electrostatic attraction (the metallic bond). The structure is therefore reshaped rather than shattered.

Recap

  • Metallic bonding is the attraction between positive metal ions and a sea of delocalised electrons.
  • The structure is a giant lattice of positive ions.
  • Delocalised electrons are free to move and are responsible for conducting electricity and heat.
  • Malleability and ductility are possible because layers of ions can slide over each other without breaking the bond.
  • The strong electrostatic forces in metallic bonds lead to high melting and boiling points.

Quick check

  1. What two types of particles are present in a metallic lattice?2 marks

3. Key Chemical Properties of Metals

In chemical reactions, metals tend to lose electrons to form positive ions (cations). This behaviour defines their key chemical properties. 1. Reaction with Acids: Most metals react with dilute acids (like hydrochloric or sulfuric acid) to produce a salt and hydrogen gas. You can observe this as fizzing or effervescence. 2. Reaction with Oxygen: Metals react with oxygen, especially when heated, to form metal oxides. For example, magnesium burns brightly in air to form white magnesium oxide. 3. Nature of Oxides: Metal oxides are typically basic. This means they are bases that can neutralise acids to form a salt and water. Some metal oxides, like sodium oxide, dissolve in water to form alkaline solutions (metal hydroxides).

Metal + Dilute Acid → Salt + Hydrogen

Metal + Oxygen → Metal Oxide

Basic Oxide (Metal Oxide) + Acid → Salt + Water

Key term

Basic Oxide: An oxide, typically of a metal, which is a base and therefore neutralises acids to form a salt and water.

Examiner insight

Examiners expect you to know that the gas produced from a metal-acid reaction is hydrogen, and to be able to describe the test for hydrogen (a lit splint gives a 'squeaky pop').

Worked example 13 marks

Zinc metal is added to a test tube containing dilute sulfuric acid. Describe one observation and write the word equation for the reaction.

  1. 1

    Step 1: Identify the reactants and reaction type. A metal (zinc) is reacting with an acid (sulfuric acid).

  2. 2

    Step 2: Predict the observation. The reaction produces hydrogen gas, so the observation would be fizzing or effervescence. The zinc metal will also dissolve.

  3. 3

    Step 3: Write the word equation. Metal + Acid → Salt + Hydrogen. So, Zinc + Sulfuric acid → Zinc sulfate + Hydrogen.

Worked example 23 marks

Copper(II) oxide, a black powder, is warmed with dilute nitric acid. Write a balanced chemical equation for this reaction.

  1. 1

    Step 1: Identify the reactants and products. This is a basic metal oxide reacting with an acid to form a salt and water. The salt will be copper(II) nitrate.

  2. 2

    Step 2: Write the formulae for the reactants and products. Reactants: CuO and HNO₃. Products: Cu(NO₃)₂ and H₂O.

  3. 3

    Step 3: Write the unbalanced equation: CuO + HNO₃ → Cu(NO₃)₂ + H₂O.

  4. 4

    Step 4: Balance the equation. There are two nitrate (NO₃) groups on the right, so we need 2HNO₃ on the left. This also gives 2 H atoms, which balances the H₂O. The final balanced equation is: CuO(s) + 2HNO₃(aq) → Cu(NO₃)₂(aq) + H₂O(l).

Recap

  • Metals react by losing electrons to form positive ions (cations).
  • Reactive metals react with dilute acids to produce a salt and hydrogen gas.
  • Metals react with oxygen to form metal oxides.
  • Most metal oxides are basic and will neutralise acids.
  • The formation of positive ions is a defining chemical characteristic of metals.

Quick check

  1. What are the two products when magnesium reacts with hydrochloric acid?2 marks
  2. Is sodium oxide an acidic, basic, or neutral oxide?1 mark

4. Metals vs. Non-Metals and Exceptions

The periodic table is broadly divided into metals (on the left and centre) and non-metals (on the top right). Their properties are generally opposites. While metals are lustrous, strong, malleable, and good conductors, solid non-metals are typically dull, brittle (shatter easily), and poor conductors (insulators). Chemically, metals form positive ions and basic oxides, whereas non-metals tend to form negative ions and acidic oxides. However, it's crucial to know the exceptions. For example, sodium is a metal but is very soft, and mercury is a metal but is liquid at room temperature. On the non-metal side, graphite (a form of carbon) is a good electrical conductor, and diamond (another form of carbon) is extremely hard with a very high melting point.

Key term

Brittle: A property of a material, typical of solid non-metals, that causes it to fracture or shatter when subjected to stress.

Examiner insight

Questions asking you to compare a metal and a non-metal are common. For full marks, you must give a property for both the metal and the non-metal, for example, 'Iron is a good conductor while sulfur is a poor conductor'.

Common pitfall

Making absolute statements like 'All metals are solid' or 'All non-metals are insulators'. Always use general terms like 'usually' or 'typically' and be aware of the key exceptions.

Worked example 13 marks

State two physical properties and one chemical property that distinguish a typical metal, like iron, from a typical non-metal, like sulfur.

  1. 1

    Physical Property 1: Iron is a good conductor of electricity, whereas sulfur is an electrical insulator.

  2. 2

    Physical Property 2: Iron is malleable and ductile, whereas sulfur is brittle and will shatter if hammered.

  3. 3

    Chemical Property: Iron reacts with oxygen to form a basic oxide (iron oxide), whereas sulfur reacts with oxygen to form an acidic oxide (sulfur dioxide).

Recap

  • Metals are on the left of the periodic table; non-metals are on the right.
  • Metals are lustrous, malleable, ductile, and good conductors; non-metals are dull, brittle, and insulators.
  • Metals form basic oxides and positive ions; non-metals form acidic oxides and negative ions.
  • Key exception: Mercury (metal) is a liquid at room temperature.
  • Key exception: Sodium (metal) is very soft.
  • Key exception: Graphite (non-metal) conducts electricity.

Quick check

  1. Name a non-metal that is a good conductor of electricity.1 mark
  2. Would you expect the oxide of phosphorus (a non-metal) to be acidic or basic?1 mark

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. Define the terms 'malleable' and 'ductile' as they apply to metals.2 marks
  2. A piece of an unknown metal has a mass of 142.2 g and a volume of 18.0 cm³. Calculate its density. Given that the density of iron is 7.9 g/cm³, is it likely that the unknown metal is iron? Justify your answer.3 marks
  3. Explain, with reference to structure and bonding, why aluminium is used for overhead power cables. You should refer to two different properties in your answer.4 marks
  4. Write a balanced chemical equation, including state symbols, for the reaction between magnesium metal and dilute hydrochloric acid.3 marks
  5. Compare the general physical properties of a typical metal, such as copper, with a typical solid non-metal, such as iodine, in terms of: (i) electrical conductivity and (ii) appearance.2 marks
  6. A student states, 'All metals are hard, magnetic solids with high melting points.' Critically evaluate this statement, giving three distinct examples that challenge its accuracy.3 marks
  7. Calcium is a metal in Group 2 of the Periodic Table. Predict the formula of its ion and the chemical nature (acidic, basic or neutral) of its oxide.2 marks
  8. Explain in detail why a metal can be bent into shape, but an ionic compound like sodium chloride shatters when hit with a hammer. Refer to the bonding and structure of both substances.5 marks
  9. Graphite is a form of the non-metal carbon, but it has a property that is more typical of a metal. Name this property and explain why graphite has it, with reference to its bonding.3 marks
  10. Describe a simple chemical test you could carry out in a school laboratory to distinguish between a piece of magnesium (a reactive metal) and a piece of silver (an unreactive metal). State the expected result for each metal.3 marks

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