Understanding Chemistry: Inorganic chemistry: Edexcel IGCSE Science Single Award Explained

Inorganic chemistry is where pattern recognition pays off: learn the trends once and apply them everywhere

The inorganic chemistry section of the Pearson Edexcel IGCSE Science Single Award (4SS0) brings together six topics that share a common thread: the behaviour of elements and compounds that do not contain carbon chains. From the violent reactions of Group 1 metals to the colour changes of flame tests, this section rewards students who learn the patterns rather than trying to memorise every individual fact.

These edexcel igcse science single award revision notes cover all six topics in the inorganic chemistry section. Each one is broken down into the specification points, with exam-focused advice on where marks are won and lost. Use these as your edexcel igcse science single award notes for targeted revision, and follow up with the self-check questions at the end.

Group 1: the alkali metals

The specification focuses on lithium, sodium and potassium. These are the first three elements of Group 1, and they share similar properties because they each have one electron in their outermost shell.

When these metals react with water, they produce a metal hydroxide and hydrogen gas. The pattern is the same for all three:

metal + water -> metal hydroxide + hydrogen

For example: 2Na(s) + 2H₂O(l) -> 2NaOH(aq) + H₂(g)

The key trend is that reactivity increases as you go down Group 1. Lithium reacts gently, fizzing on the surface. Sodium reacts more vigorously, moving rapidly across the surface and sometimes producing a yellow flame. Potassium reacts violently, igniting with a lilac flame. This trend exists because, as you move down the group, the outermost electron is further from the nucleus and easier to lose.

The specification asks you to use knowledge of trends in Group 1 to predict the properties of other alkali metals. If asked about rubidium (below potassium), you should predict that it reacts even more violently with water than potassium does.

Group 7: the halogens

The specification focuses on chlorine, bromine and iodine. You need to know their physical states at room temperature and their colours:

Halogen	Colour	State at room temperature
Chlorine	Pale yellow-green	Gas
Bromine	Red-brown	Liquid
Iodine	Dark grey / purple vapour	Solid

The trend in Group 7 is the opposite of Group 1: reactivity decreases as you go down the group. Chlorine is more reactive than bromine, which is more reactive than iodine. The melting and boiling points increase going down the group, which is why chlorine is a gas, bromine is a liquid, and iodine is a solid at room temperature.

Exam tip: If you are asked to predict the properties of astatine (below iodine in Group 7), state that it would be a solid with a higher melting point than iodine and that it would be less reactive than iodine. Follow the trend.

Gases in the atmosphere

You need to know the approximate percentages by volume of the four most abundant gases in dry air:

Nitrogen: approximately 78%
Oxygen: approximately 21%
Argon: approximately 0.9%
Carbon dioxide: approximately 0.04%

The specification also requires you to describe how to determine the percentage of oxygen in air experimentally. The classic method involves passing air repeatedly over heated copper in a sealed apparatus. The copper reacts with the oxygen to form copper oxide, removing the oxygen from the air sample. By measuring the volume of air before and after, you can calculate the proportion that was oxygen. The expected result is approximately one-fifth (21%).

You must also be able to describe the combustion of elements in oxygen:

Magnesium burns with a bright white flame, producing magnesium oxide (a white powder): 2Mg + O₂ -> 2MgO
Hydrogen burns with a squeaky pop, producing water: 2H₂ + O₂ -> 2H₂O
Sulfur burns with a blue flame, producing sulfur dioxide (a colourless, choking gas): S + O₂ -> SO₂

The specification requires you to know that carbon dioxide is a greenhouse gas and that increasing amounts in the atmosphere may contribute to climate change. This links back to the carbon cycle in the biology section of this edexcel igcse single award course.

Reactivity series

The reactivity series ranks metals in order of how readily they react. The specification gives this order, from most reactive to least reactive:

Potassium > Sodium > Lithium > Calcium > Magnesium > Aluminium > Zinc > Iron > Copper > Silver > Gold

You can establish this order by observing reactions with water and with dilute hydrochloric or sulfuric acid. The most reactive metals (potassium, sodium) react vigorously with cold water. Moderately reactive metals (magnesium, zinc, iron) react with dilute acids but not noticeably with cold water. The least reactive metals (copper, silver, gold) do not react with water or dilute acids.

Rusting of iron

The specification requires you to know the conditions under which iron rusts: iron rusts when it is exposed to both water and oxygen. If either is absent, rusting does not occur.

Prevention methods include:

Barrier methods: painting, oiling, greasing, or plastic coating the iron to keep water and oxygen away from the surface.
Galvanising: coating the iron with a layer of zinc. Even if the zinc layer is scratched, the zinc corrodes preferentially because it is more reactive than iron, sacrificing itself to protect the iron underneath.

Acids and alkalis

The pH scale runs from 0 to 14. The specification classifies solutions as:

pH range	Classification
0 to 3	Strongly acidic
4 to 6	Weakly acidic
7	Neutral
8 to 10	Weakly alkaline
11 to 14	Strongly alkaline

Litmus paper turns red in acidic solutions and blue in alkaline solutions. Universal indicator gives a range of colours depending on the pH, allowing a more precise measurement.

In aqueous solution, acids are a source of hydrogen ions (H⁺) and alkalis are a source of hydroxide ions (OH^-). Neutralisation occurs when an acid reacts with an alkali:

H⁺(aq) + OH^-(aq) -> H₂O(l)

Common mistake: Confusing the pH scale with acidity strength. A pH of 1 is more acidic than a pH of 3, not the other way around. The lower the number, the stronger the acid. Students sometimes write that a higher pH means a stronger acid because they associate "higher" with "more." Double-check the direction.

Chemical tests

This topic is highly specific and rewards pure recall. The specification lists the following tests:

Tests for gases

Gas	Test	Positive result
Hydrogen	Hold a burning splint near the gas	Squeaky pop
Oxygen	Hold a glowing splint in the gas	Splint relights
Carbon dioxide	Bubble through limewater	Limewater turns milky (cloudy)
Ammonia	Hold damp red litmus paper in the gas	Litmus turns blue
Chlorine	Hold damp litmus paper in the gas	Litmus is bleached white

Flame tests

Ion	Flame colour
Li⁺	Crimson red
Na⁺	Yellow
K⁺	Lilac
Ca²⁺	Orange-red
Cu²⁺	Blue-green

Test for carbonates

Add dilute hydrochloric acid to the substance. If it contains carbonate ions (CO₃^2-), the acid reacts to produce carbon dioxide gas, which turns limewater milky when bubbled through it.

Test for water

Add the liquid to anhydrous copper(II) sulfate, which is a white powder. If water is present, the powder turns blue as it forms hydrated copper(II) sulfate.

Self-check questions

Write the word equation for the reaction of potassium with water and predict how vigorous the reaction would be compared to sodium.
State the colour and physical state of each of the three halogens at room temperature.
Name the four most abundant gases in dry air and give their approximate percentages.
Place these metals in order of reactivity from most to least reactive: iron, magnesium, copper, potassium, zinc.
State two conditions required for iron to rust and describe two methods of rust prevention.
What is the pH range for a weakly alkaline solution?
Describe the flame test colour for each of these ions: Li⁺, Na⁺, K⁺, Ca²⁺, Cu²⁺.
Explain how you would test a gas to confirm it is carbon dioxide.

Pulling it all together

The chemistry: inorganic chemistry edexcel igcse section is wide but not deep. Each topic has a small number of key facts, trends and tests that you need to know precisely. The flame test colours, the gas tests, the reactivity series order, the pH classifications: these are all items where accuracy is everything. A "yellowish" flame is not the same as a "crimson" flame, and examiners will not award marks for vague descriptions.

For your igcse 4ss0 chemistry: inorganic chemistry revision, create flashcards for the fact-heavy topics (flame tests, gas tests, halogen properties) and use them daily in the weeks before the exam. For the conceptual topics (trends in Groups 1 and 7, the reactivity series, rusting), make sure you can explain the reasoning behind the patterns, not just state what happens.

These edexcel igcse science single award notes are your starting point. Move on to edexcel igcse science single award practice questions to see how these facts are tested in context. The edexcel igcse science single award explained format here gives you the theory; the exam rewards its application. The Green Bridge CBT platform lets you practise inorganic chemistry questions with instant feedback, so you can close the gap between what you know and what you can demonstrate under timed conditions.