IGCSE Chemistry — The Periodic Table: Notes, Practice Questions & Worked Solutions

IGCSE Chemistry 0620 · Topic 8: The Periodic Table

The Periodic Table

Elements are arranged by increasing proton number, and their position tells you almost everything about how they’ll react — especially for Group I and Group VII, which show clear, opposite trends in reactivity.

1. Groups and Periods

A group (vertical column) contains elements with the same number of outer-shell electrons, giving them similar chemical properties. A period (horizontal row) shows elements with the same number of electron shells.

2. Group I — The Alkali Metals

Reactivity increases down the group (the outer electron is further from the nucleus and more easily lost), while melting point decreases down the group.

2Na + 2H₂O → 2NaOH + H₂

3. Group VII — The Halogens

Reactivity decreases down the group (harder to gain an extra electron as atoms get bigger), while melting and boiling points increase down the group.

Worked example — displacement reactions Chlorine gas is bubbled through a solution of potassium bromide. Predict and explain what happens.
Chlorine is more reactive than bromine (higher up Group VII), so it displaces bromine from potassium bromide solution: Cl₂ + 2KBr → 2KCl + Br₂. The solution turns from colourless to orange/brown as bromine is formed.

4. Transition Elements and Noble Gases

Transition elements (the central block) are typically dense, have high melting points, form coloured compounds, show variable oxidation states, and are often good catalysts.

Noble gases (Group VIII/0) are unreactive because they already have a full outer shell of electrons. Uses include helium (balloons, airships — low density), neon (advertising lights), and argon (filling light bulbs to prevent the filament reacting with oxygen).

Common mistakes to watch for

Mixing up the Group I and Group VII trends — they go in OPPOSITE directions for reactivity (I increases down, VII decreases down).
Forgetting that a more reactive halogen displaces a less reactive one from solution, not the other way round.
Describing noble gases as “never reacting” — they are extremely unreactive, but a few compounds of heavier noble gases do exist (beyond IGCSE scope, but “unreactive” rather than “never reacts” is the safer wording).

Key Vocabulary Recap

Group — a vertical column of the periodic table, same number of outer electrons

Period — a horizontal row, same number of electron shells

Displacement reaction — a more reactive element takes the place of a less reactive one in a compound

Syllabus Reference

This note covers IGCSE Chemistry 0620 Topic 8, The Periodic Table: groups and periods, periodic trends, Group I alkali metals, Group VII halogens, transition elements, and noble gases.

Practice questions

IGCSE Chemistry 0620 · Topic 8: The Periodic Table — Practice Question Bank (no answers)

The Periodic Table — Practice

Covers: groups, periods, Group I/VII trends, transition elements, and noble gases. 10 questions.

Q1 Core

Explain how elements are arranged in the Periodic Table.

Q2 Core

State how reactivity changes down Group I, and explain why.

Q3 Core

Write the word and symbol equation for the reaction between sodium and water.

Q4 Core

State how reactivity changes down Group VII, and explain why.

Q5 Extended

Chlorine gas is bubbled through a solution of potassium bromide. Predict what you would observe, and write the symbol equation.

Q6 Extended

Explain why fluorine can displace chlorine from a solution of a chloride, but chlorine cannot displace fluorine.

Q7 Core

State three typical physical properties of transition elements.

Q8 Core

Explain why the noble gases are so unreactive.

Q9 Core

Give one everyday use of helium, and explain why it is suitable.

Q10 Core

Explain the difference between a group and a period in the Periodic Table.

Worked solutions

Show worked solutions

IGCSE Chemistry 0620 · Topic 8: The Periodic Table — Solutions

The Periodic Table — Practice: Solutions

How are elements arranged?

✓Elements are arranged in order of increasing proton (atomic) number, into periods (rows, elements with the same number of electron shells) and groups (columns, elements with the same number of outer-shell electrons).

Group I reactivity trend and reason.

✓Reactivity increases down Group I. Going down the group, the single outer electron is in a shell further from the nucleus, so it is more easily lost — making the atom more reactive.

Sodium + water equation.

✓sodium + water → sodium hydroxide + hydrogen; 2Na + 2H₂O → 2NaOH + H₂

Group VII reactivity trend and reason.

✓Reactivity decreases down Group VII. Going down the group, the outer shell needing one more electron is further from the nucleus, so it is harder for the atom to attract and gain an extra electron — making the atom less reactive.

Cl₂ + KBr solution.

✓The colourless solution turns orange/brown, as chlorine (more reactive) displaces bromine from potassium bromide. Cl₂ + 2KBr → 2KCl + Br₂

Why can F displace Cl but not vice versa?

✓Fluorine is more reactive than chlorine (higher up Group VII), so it can displace the less reactive chlorine from a chloride solution. Chlorine, being less reactive than fluorine, cannot displace the more reactive fluorine from a fluoride solution — a less reactive halogen can never displace a more reactive one.

Three properties of transition elements.

✓Any three of: high density, high melting point, form coloured compounds, show variable oxidation states, often useful as catalysts.

Why are noble gases unreactive?

✓Noble gas atoms already have a full outer shell of electrons, so they have no tendency to gain, lose, or share electrons with other atoms — making them extremely unreactive.

Use of helium.

✓Helium is used to fill balloons and airships, because it has a very low density (making things float) and, being a noble gas, is non-flammable (unlike hydrogen), making it much safer.

Q10

Group vs period.

✓A group is a vertical column, containing elements with the same number of outer-shell electrons (and hence similar chemical properties). A period is a horizontal row, containing elements with the same number of electron shells.

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