CHEMISTRY · Stage 7 · Chapter 6: The Earth and Plate Tectonics

Chemistry Stage 7 Comprehensive Review

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Stage 7 Comprehensive Review — Alhussan International Academy — Chemistry (Stages 7–9) notes: Revise and connect the main ideas of Stage 7 chemistry: particles, elements, reactions, acids and the Earth.Particle model — all matter is made of particles.Solids — particles are close …

Changes of state
Non-metals
Comparing elements
Reactants and products
Signs of reaction
Neutralisation

Section 1 of 8Particles and states of matter

Particle model
- all matter is made of particles.
Solids
- particles are close together in fixed positions and vibrate.
Liquids
- particles are close but can move past each other.
Gases
- particles are far apart and move randomly and quickly.
Changes of state
- melting, freezing, evaporation, boiling and condensation are physical changes.
- Energy goes in during melting and boiling and comes out in freezing and condensing.
- A heating curve has flat sections at the melting and boiling points.
- Models have limits.

Section 2 of 8Elements, compounds and mixtures

Element
- a substance with only one type of atom, listed in the periodic table by atomic number.
Compound
- different elements chemically bonded in a fixed ratio, with new properties.
- Formulae show the number of atoms, for example H₂SO₄.
Mixture
- substances that are not bonded and can be separated by physical methods.
- Methods include filtration, evaporation, distillation and chromatography.

Section 3 of 8Metals, non-metals and alloys

Metals
- they are shiny, malleable and conduct because of delocalised electrons.
Non-metals
- they are mostly brittle insulators with low melting points.
Alloys
- they are harder than pure metals because atoms of different sizes disrupt the layers.
Comparing elements
- properties can be shown in a bar chart, where the tallest bar is the highest value, and symbols are matched to the periodic table.

Section 4 of 8Chemical reactions

Reactants and products
- reactants form products, with atoms rearranged but conserved.
Signs of reaction
- colour change, gas, precipitate and temperature change.
Rusting
- it needs oxygen and water.

Section 5 of 8Acids and alkalis

pH scale
- acids have pH below 7 and alkalis above 7.
Neutralisation
- acid plus base gives a salt and water.
Acids with metals
- they give hydrogen.
Acids with carbonates
- they give carbon dioxide.
Acid rain
- it forms from sulfur dioxide and nitrogen oxides.
Testing lake water
- add a few drops of universal indicator and match the colour to the pH chart.

Test	Result
Hydrogen	Squeaky pop
Carbon dioxide	Limewater turns cloudy
Acid	Universal indicator turns red to yellow

Section 6 of 8Lakes and pH

Calm bays
- more carbon dioxide dissolves, and carbon dioxide is acidic, so the water is more acidic.
Moving water
- less carbon dioxide dissolves, so the water is more alkaline.
Acid rain effect
- if rain became more acidic, the pH of lakes might decrease.
Tilapia
- they prefer water of pH 6 to 9, and many survive pH 5 to 10, so only lakes within these ranges are suitable.

Section 7 of 8The Earth

Layers
- the Earth has a crust, mantle, liquid outer core and solid inner core.
Plates
- the lithosphere is broken into plates driven by mantle convection.
Boundaries
- plate boundaries produce earthquakes, volcanoes and fold mountains.
Wegener's theory
- it was supported by evidence from fossils, rocks, coastlines and sea-floor spreading.

Section 8 of 8Practical skills

Method
- name apparatus and write a method with control variables.
Results
- record results in a table with units.
Graphs
- draw graphs with labelled axes and a line of best fit.
Conclusion
- write a conclusion supported by data.
Safety
- wear eye protection, tie back hair, handle acids and hot objects carefully, and use fume cupboards for toxic gases.
Evaluation
- spot anomalous results, suggest improvements and decide whether data are reliable.

Last updated: 13 October 2026