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How metal atoms are bonded, why metals have their properties, and the particle model of solids, liquids and gases.
Specification references this topic covers: AQA 5.2.1, 5.2.2, 5.3.1, 5.8.1; Edexcel C1.33, C1.40, C2.1, C2.2, C2.3, C2.4, C6.16.
Why can you bend a copper wire but not snap it? Why does a puddle turn to ice and then to steam? Both questions come down to how tiny particles are arranged and held together.
This matters because it explains why we use metals for pans, wires and bridges. It also explains why water can be a solid, a liquid or a gas.
By the end you will be able to describe metallic bonding and explain why metals behave as they do. You will describe solids, liquids and gases. You will name changes of state and predict the state of a substance.
A metal is a giant structure of positive metal ions in a regular pattern. Each atom has let go of its outer electrons. These electrons are delocalised, which means they are free to move through the whole structure.
You can picture a sea of electrons with the ions sitting in it. Metallic bonding is the strong electrostatic attraction between the positive ions and the delocalised electrons. It holds the structure together.
Metals have high melting and boiling points. A lot of energy is needed to overcome the strong attraction between the ions and the electrons. They are good conductors of heat and electricity, because the delocalised electrons carry energy and charge through the metal.
Metals are malleable, which means they can be hammered into shape. They are also ductile, which means they can be drawn into wires.
The layers of ions can slide over each other, like a pack of cards. The bonding does not break, because the electrons still hold the ions together.
In a solid, the particles are close together in a regular pattern and only vibrate in place. In a liquid, they are close together but random, and they slide past each other. In a gas, they are far apart and move quickly in all directions.
A solid has a fixed shape and volume. A liquid has a fixed volume but takes the shape of its container. A gas has no fixed shape or volume and can be squashed.
State symbols show the state in an equation. They are (s) solid, (l) liquid and (g) gas. The symbol (aq) means dissolved in water.
Melting is solid to liquid. Freezing is liquid to solid. Boiling or evaporating is liquid to gas. Condensing is gas to liquid. Sublimation is solid straight to gas.
These are physical changes. The particles are not changed, only their energy and arrangement. At the melting point, they have enough energy to overcome some of the forces between them. At the boiling point, they can break free from each other.
To predict the state, compare the temperature with the two points. Below the melting point it is a solid. Between them it is a liquid. Above the boiling point it is a gas. Bromine melts at −7 °C and boils at 59 °C, so at 20 °C it is a liquid.
The stronger the forces between particles, the more energy is needed to melt or boil the substance. So the melting and boiling points are higher. Think of a crowd holding hands tightly. It takes more effort to pull them apart.
Ionic compounds and metals have strong forces, so they are solids at room temperature. Simple molecular substances have weak forces between their molecules, so they are often liquids or gases.
When you explain a change of state, say what is overcome. For water boiling it is the weak forces between molecules. For sodium chloride melting it is the strong attraction between ions.
The simple particle model shows particles as solid spheres. It explains the arrangement in solids, liquids and gases very well. But it has limits.
It does not show the forces between particles. It shows the spaces between them as much smaller than they really are. It treats all particles as the same size and shape, though real atoms and molecules differ.
If you are asked to evaluate a model, give one thing it explains well and one limitation.
Metals are positive ions in a sea of delocalised electrons. This makes them good conductors and malleable.
Solids are fixed and close. Liquids are close and random. Gases are far apart and fast.
Below the melting point is a solid. Between the two points is a liquid. Above the boiling point is a gas.
The particle model leaves out the forces between particles.
Name the change of state when a solid turns into a liquid.
Answer: melting
Chlorine melts at −101 °C and boils at −34 °C. What state is chlorine at 20 °C?
Answer: gas
Explain why copper conducts electricity and can be drawn into wires.
Answer: Delocalised electrons carry charge, and layers of ions slide over each other without breaking the bonding.
Metallic bonding and states of matter practice questions for GCSE Combined Science Chemistry. Try each one, then open the answer. Easy questions come first.
What is the name for the change from liquid to gas?
Answer: boiling
What is the state symbol for a solution in water?
Answer: (aq)
Which type of particle in a metal is delocalised?
Answer: electrons
Are the particles in a solid close together or far apart?
Answer: close together
What is the name for the change from gas to liquid?
Answer: condensing
What does the state symbol (s) mean?
Answer: solid
Ethanol melts at −114 °C and boils at 78 °C. What state is ethanol at 20 °C?
Answer: liquid
Iron melts at 1538 °C. What state is iron at 1600 °C, assuming it has not reached its boiling point?
Answer: liquid
Longer questions in the style of a written paper, with the marking points. These are Yumio practice questions.
The table shows the melting point and boiling point of two substances. Substance A: melting point −219 °C, boiling point −183 °C. Substance B: melting point 801 °C, boiling point 1413 °C. (a) State the state of substance A at 20 °C. [1 mark] (b) State the state of substance B at 1000 °C. [1 mark] (c) Substance B conducts electricity when molten but not when solid. Explain why. [2 marks]
Answer: (a) gas (b) liquid (c) When molten the ions are free to move and carry charge. In the solid the ions are fixed in place.
(a) Describe the arrangement and movement of the particles in a liquid. [2 marks] (b) Explain how metals can conduct electricity and be bent without breaking. [2 marks]
Answer: (a) The particles are close together in a random arrangement and move past each other. (b) The delocalised electrons carry the charge. The layers of ions slide over each other.
Saying metals conduct because their ions move
The positive ions are fixed. It is the delocalised electrons that move.
Saying the particles themselves get hotter or bigger when a substance melts
The particles stay the same. They gain energy and move more.
Saying the covalent bonds break when a simple molecular substance boils
Only the weak intermolecular forces are overcome.
Using (aq) for a pure liquid
(aq) means dissolved in water. A pure liquid is (l).
Metallic bonding and states of matter is on both Foundation and Higher papers for GCSE Combined Science Chemistry, aimed at around grade 4.
Saying metals conduct because their ions move. The positive ions are fixed. It is the delocalised electrons that move.
Open Show answer under each question on this page. The questions are Yumio practice questions, not past exam questions.
See how the papers are set: AQA Combined Science papers and Edexcel Combined Science papers.
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