How is the Periodic Table arranged and what does an element's position tell you?

The Periodic Table is arranged in order of increasing proton number. Vertical columns are groups and horizontal rows are periods. The group number equals the number of electrons in the outer shell, and the period number equals the number of electron shells. So an element's position tells you its electron arrangement: for example, an element in Group II, Period 3 has 2 electrons in its outer shell and 3 shells in total.

What are the trends down Group I, the alkali metals?

The Group I metals (such as lithium, sodium and potassium) all have one outer electron and become more reactive as you go down the group. Going down, the atoms get larger and the outer electron is further from the nucleus and more easily lost, so reactions with water become more vigorous. They are soft, low-density metals that react with water to form an alkaline hydroxide and hydrogen.

What are the trends down Group VII, the halogens?

The Group VII non-metals (such as chlorine, bromine and iodine) all have seven outer electrons and become less reactive as you go down the group. Going down, the atoms get larger so it is harder to gain the one electron needed to fill the outer shell. They also get darker and denser down the group, going from a pale green gas (chlorine) to a red-brown liquid (bromine) to a dark grey solid (iodine).

What is special about the transition metals?

The transition metals form a block in the centre of the Periodic Table, between Groups II and III. Compared with the Group I metals, they are harder, stronger, denser and have higher melting points. They are also typically less reactive, form coloured compounds, and often act as catalysts. Iron, copper and zinc are common examples used in everyday materials and industry.

How is the Periodic Table topic assessed in N(A)-Level Science 5107?

It is examined in the two Chemistry papers. Paper 3 (multiple choice, 20 marks) tests linking position to electron arrangement, the group trends, and identifying transition metals. Paper 4 (structured, 30 marks) asks you to explain a group trend in terms of atom size and electron arrangement, predict a property from position, and contrast the transition metals with the Group I metals. A Periodic Table is provided in the multiple choice paper.

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The Periodic Table (Singapore N(A)-Level Science Chemistry 5107): how the table is arranged into groups and periods, the trends down Group I, Group VII and Group 0, and the difference between metals, non-metals and the transition block

A Singapore N(A)-Level Science Chemistry (SEAB 5107) overview of the Periodic Table. How the table is arranged into groups and periods and how position links to electron arrangement, the trends down the Group I metals, the Group VII non-metals and the Group 0 noble gases, and how metals, non-metals and the transition block differ, with links to every dot point.

Generated by Claude Opus 4.85 min readSEAB-5107Updated 2026-06-13

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this topic is really about
The Periodic Table and periods
Groups and their trends
Metals, non-metals and the transition block
How this topic is examined
Check your knowledge

What this topic is really about

The Periodic Table is the great organising tool of chemistry: it arranges the elements so that those with similar properties line up, and it lets you predict an element's behaviour from its position. Once you connect position to electron arrangement, the trends and the families fall into place. This guide ties the three dot points together and links to each one for the worked answers and practice.

The complete set of dot-point pages for this topic lives at /sg-n-level/chemistry/syllabus/the-periodic-table.

The Periodic Table and periods

The Periodic Table and periods explains how the table is arranged by increasing proton number into groups (columns) and periods (rows), and how position links to electron arrangement. The group number gives the number of outer electrons, and the period number gives the number of shells.

Groups and their trends

Groups and their trends covers the three families you need: Group I (the alkali metals, getting more reactive down the group), Group VII (the halogens, getting less reactive down the group), and Group 0 (the noble gases, very unreactive because they have full outer shells).

Metals, non-metals and the transition block

Metals, non-metals and the transition block locates the metals on the left and the non-metals on the right, compares their properties, and describes the transition metals in the centre, which are harder, denser, often coloured in their compounds, and useful as catalysts.

How this topic is examined

Read position as electron arrangement. Group number is outer electrons, period number is shells.
Explain group trends with atom size. Down Group I the outer electron is further out and lost more easily (more reactive); down Group VII it is harder to gain an electron (less reactive).
Contrast transition metals with Group I. Harder, denser, higher melting points, less reactive, coloured compounds, catalytic.

Check your knowledge

A mix of recall, reasoning and prediction questions covering the Periodic Table. Attempt them under timed conditions, then check against the solutions.

State what the group number and the period number tell you about an atom. (2 marks)
An element has the electron arrangement 2, 8, 7. State its group and period. (2 marks)
Explain why reactivity increases down Group I. (2 marks)
Explain why reactivity decreases down Group VII. (2 marks)
State two ways in which the transition metals differ from the Group I metals. (2 marks)

Sources & how we know this

Singapore-Cambridge GCE Normal (Academic) Level Science (Physics, Chemistry) and Science (Chemistry, Biology) (Syllabus 5107) — Singapore Examinations and Assessment Board (2026)
Cambridge Assessment International Education, working with SEAB on the Singapore-Cambridge GCE N(A)-Level — Cambridge Assessment International Education (2026)