Understanding Inorganic chemistry: Group 1 (alkali metals) – lithium, sodium and potassium to Reactivity series: Edexcel IGCSE Chemistry Explained

Groups 1 and 7 demonstrate the power of the Periodic Table: within each group, elements share a family resemblance, yet a clear trend in reactivity runs from top to bottom.

The inorganic chemistry section of the Edexcel IGCSE Chemistry specification is where abstract ideas about electron configuration meet observable, sometimes dramatic, chemical behaviour. Lithium fizzing gently on water, potassium igniting with a lilac flame, chlorine bleaching indicator solution: these are the reactions that bring the Periodic Table to life. This article covers Group 1 (alkali metals), Group 7 (halogens), gases in the atmosphere, and the reactivity series. These topics are examined in almost every session, so thorough preparation pays dividends.

These edexcel igcse chemistry revision notes cover the igcse 4ch1 inorganic chemistry: group 1 (alkali metals) – lithium, sodium and potassium to reactivity series material with the precision the exam demands.

Group 1: the alkali metals

Lithium, sodium and potassium are the three Group 1 metals named in the specification. They are soft metals with low melting points (relative to other metals), low densities, and a single electron in their outer shell. It is that single outer electron that defines their chemistry.

Reactions with water:

All three alkali metals react with cold water to produce a metal hydroxide and hydrogen gas:

2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

The observations differ in vigour:

• Lithium floats, fizzes steadily, and slowly dissolves.
• Sodium floats, melts into a ball, fizzes vigorously, and moves rapidly across the surface.
• Potassium floats, melts, fizzes violently, and the hydrogen produced ignites with a lilac flame. The metal may spit.

The increasing vigour from lithium to potassium demonstrates the trend in reactivity going down Group 1.

Reactions with oxygen (air): the alkali metals tarnish quickly in air, forming metal oxides. Potassium tarnishes fastest. This provides further evidence for the trend in reactivity.

Explaining the trend: Going down Group 1, atoms get larger because each successive element has one more electron shell. The outer electron is further from the nucleus and is shielded by more inner electron shells. This means the outer electron is held less tightly by the nuclear charge and is lost more easily. Since reactivity in metals depends on how readily they lose their outer electron, reactivity increases down the group.

Group 7: the halogens

Chlorine, bromine and iodine are the three Group 7 elements covered in the specification. Unlike the alkali metals, reactivity decreases down Group 7.

The trend in physical properties going down the group: colour darkens, boiling point increases, and the elements become less volatile.

Displacement reactions provide evidence for the trend in reactivity. A more reactive halogen can displace a less reactive halide from solution:

Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq)

Chlorine displaces bromine because chlorine is more reactive. The solution turns from colourless to orange-brown as bromine is released. Bromine can displace iodine, but iodine cannot displace either chlorine or bromine.

Explaining the trend: Going down Group 7, atoms get larger. The outer shell is further from the nucleus and more shielded by inner electrons. It becomes harder for the atom to attract an additional electron to fill its outer shell. Since reactivity in non-metals depends on how readily they gain electrons, reactivity decreases down the group.

Gases in the atmosphere

Dry air is approximately 78% nitrogen, 21% oxygen, 0.9% argon, and 0.04% carbon dioxide by volume. You need to know these approximate percentages.

Determining the percentage of oxygen in air: Pass air repeatedly over heated iron wool (or burn phosphorus in a sealed container of air). The oxygen reacts, and the reduction in volume indicates the proportion of oxygen. With iron: the iron reacts with oxygen to form iron oxide, and the volume of gas decreases by about one-fifth.

Combustion of elements in oxygen:

• Magnesium burns with a bright white flame: 2Mg(s) + O₂(g) → 2MgO(s)
• Hydrogen burns with a squeaky pop: 2H₂(g) + O₂(g) → 2H₂O(l)
• Sulfur burns with a blue flame: S(s) + O₂(g) → SO₂(g)

Carbon dioxide: It can be formed by the thermal decomposition of metal carbonates. For instance:

CuCO₃(s) → CuO(s) + CO₂(g)

Carbon dioxide is a greenhouse gas. Increasing levels in the atmosphere from burning fossil fuels may contribute to climate change by trapping infrared radiation that would otherwise escape into space.

The reactivity series

Metals can be ranked in a reactivity series based on how vigorously they react with water and with dilute acids.

Displacement reactions also confirm the order. A more reactive metal displaces a less reactive metal from a solution of its salt or from its oxide:

Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Zinc displaces copper because zinc is more reactive. The blue solution fades, and a brown deposit of copper appears.

Rusting of iron: Iron rusts when exposed to both water and oxygen. Both must be present. Rusting is prevented by:

• Barrier methods: painting, oiling, greasing, plastic coating (keep water and oxygen away).
• Galvanising: coating iron with zinc. Even if the zinc layer is scratched, zinc is more reactive than iron, so it reacts preferentially.
• Sacrificial protection: attaching blocks of a more reactive metal (e.g. zinc or magnesium) to the iron structure. The more reactive metal corrodes instead of the iron.

Oxidation and reduction (redox):

• Oxidation is the gain of oxygen or the loss of electrons.
• Reduction is the loss of oxygen or the gain of electrons.
• A redox reaction involves both occurring simultaneously.
• An oxidising agent causes oxidation (and is itself reduced).
• A reducing agent causes reduction (and is itself oxidised).

Common mistakes

• Reversing the reactivity trend for Group 7. Reactivity increases down Group 1 but decreases down Group 7. Many students apply the Group 1 trend to both groups.
• Confusing displacement and decomposition. Displacement involves one element replacing another in a compound. Decomposition involves one substance breaking down into simpler substances. They are not interchangeable terms.
• Stating that aluminium is unreactive. Aluminium is actually quite reactive, but its oxide layer protects it. The exam expects you to explain this distinction.
• Forgetting that rusting requires both water and oxygen. Students often cite one without the other.
• Using "oxidation" and "reduction" inconsistently. If you define oxidation as loss of electrons in one answer, do not switch to "gain of oxygen" in another without acknowledging both definitions apply.

Linking topics across the exam

The edexcel igcse chemistry inorganic chemistry: group 1 (alkali metals) – lithium, sodium and potassium to reactivity series material is not tested in isolation. Exam questions frequently combine reactivity with displacement equations, with redox definitions, and with predictions about unfamiliar metals. The inorganic chemistry: group 1 (alkali metals) – lithium, sodium and potassium to reactivity series edexcel igcse content also overlaps with metal extraction (you need the reactivity series to decide whether carbon reduction or electrolysis is required) and with acids and bases (metals above hydrogen in the series react with dilute acid; those below do not).

A strong candidate can answer a question that moves seamlessly from "place these metals in order of reactivity" through "write the balanced equation" to "identify the oxidising and reducing agents," all within a single five or six mark response. That fluency comes from understanding the connections between these igcse 4ch1 inorganic chemistry: group 1 (alkali metals) – lithium, sodium and potassium to reactivity series topics, not just memorising each one separately.

The edexcel igcse chemistry explained here maps directly to the mark scheme language. Use that language in your answers. "The outer electron is further from the nucleus and is more shielded" is the phrasing that earns the reactivity trend marks. Paraphrasing it weakly ("the electron is not held as tightly") may earn partial credit but risks missing the key point the examiner needs to see.

Self-check questions

1. Write a balanced equation with state symbols for the reaction of potassium with water.
2. Explain why reactivity increases down Group 1 in terms of electronic configuration.
3. Predict what would happen if chlorine water is added to a solution of potassium iodide. Write the equation.
4. A student places iron filings into copper sulfate solution. Describe and explain what happens.
5. A ship's hull is protected by zinc blocks bolted to the surface. Explain how this prevents the iron hull from rusting.

These edexcel igcse chemistry practice questions test the core skills the exam demands: recalling the reactivity order, writing balanced equations, and explaining trends in terms of atomic structure. For more inorganic chemistry: group 1 (alkali metals) – lithium, sodium and potassium to reactivity series edexcel igcse revision material, the Green Bridge CBT platform offers topic-matched edexcel igcse chemistry notes and practice sets aligned directly to the specification.