The Periodic Table (Years 7–11) — Science

How the elements are organised — periods, groups, metals and the key groups to know.

There are around 118 known elements — the pure building blocks that make up everything in the universe. Left as a random list they would be chaos. The periodic table lines them all up in order and, brilliantly, sorts the ones that behave alike into the same columns. It is the single most useful chart in all of chemistry.

Why this matters: the table lets you predict how an element will react before you ever put it in a test tube, just from where it sits. That is a superpower — and it is why chemists call it the map of matter.

Group 1 (alkali metals) and group 0 (noble gases)

Reading the layout

A period is a row (across); a group is a column (down).

Every element is placed in order of its atomic number — the number of protons in its atom. The grid then has two directions:

Rows are called periods.
Columns are called groups. Elements in the same group share similar chemical properties, because they have the same number of outer-shell electrons — and it is those outer electrons that control how an element reacts.

Picture the table as a seating plan at a huge dinner: people at the same table (group) share the same interests (react in similar ways), while the row you are in (period) just tells you how far along you sit.

Metals and non-metals

Metals sit left and centre; non-metals cluster top-right, split by a staircase.

A diagonal staircase splits the table. Metals sit on the left and in the middle — the vast majority of elements, and the ones that tend to be shiny, strong and good at conducting electricity. Non-metals huddle on the right-hand side, and are often dull, brittle and poor conductors. The big block of metals wedged in the centre are the transition metals — familiar names like iron, copper and gold live there.

Three groups worth knowing

Group	Name	Example	Behaviour
Group 1	Alkali metals	Sodium	Soft, very reactive metals
Group 7	Halogens	Chlorine	Reactive non-metals
Group 0	Noble gases	Helium	Unreactive gases

Predicting from position.

The group number tells you the number of outer-shell electrons.

Suppose you are told an element is in group 1. Straight away you know: it is a metal, it sits on the far left, it is soft and very reactive, and it has one outer-shell electron just like sodium. You worked all that out purely from the group number — no experiment needed. That is the whole point of the table.

Common mix-up: do not swap the words period and group. Periods run across (rows); groups run down (columns). It is the group — the column — that tells you how an element reacts, because a column shares outer electrons.

Memory hook: think “grouPs go dowP” (columns), and elements in a group are chemical family members that behave the same. Group number ≈ number of outer electrons.