Key Stage 3 science · Chemistry – The Periodic Table

KS3 Periodic Table: a guide for parents

The Periodic Table organises all the known elements so that patterns in their properties show up. In Years 7 to 9 children learn how it is laid out, why Mendeleev arranged it as he did, how metals and non-metals differ, and how to use the table to predict how elements and their oxides will behave.

The Periodic Table, explained

An element is a substance made of only one kind of atom, and 118 are known today, each with its own place in the Periodic Table. Each has a name and a symbol of one or two letters, sometimes taken from an older Latin name: Na for sodium, K for potassium, Fe for iron. The table is arranged in rows called periods and columns called groups. Elements in the same group have similar chemical properties, which is why the table is so useful: knowing how one element behaves tells you a lot about its neighbours.

Pupils learn about Dmitri Mendeleev, who published his table in 1869. He arranged the elements known at the time mainly in order of atomic mass, and started a new row so that elements with similar properties lined up in the same column. He left gaps where no known element fitted and predicted the properties of the missing ones. Gallium, found in 1875, and germanium, found in 1886, matched his predictions closely, which convinced scientists the pattern was real. In places he even swapped elements out of mass order so that they sat with their chemical relatives. Modern tables are ordered by atomic number, which keeps those patterns without the exceptions.

Most elements are metals, found on the left and in the middle, and non-metals sit on the right. Metals are usually shiny, good conductors of heat and electricity, malleable (they can be hammered into shape) and have high melting points. Non-metals tend to be dull, brittle when solid, poor conductors and have lower melting points. There are exceptions that make good discussion points: mercury is a liquid metal, sodium is soft enough to cut with a knife, and graphite, a form of carbon, conducts electricity.

Patterns in groups allow predictions. Group 1, the alkali metals (lithium, sodium and potassium), are soft and very reactive, and react with water to make hydrogen and an alkaline solution. They become more reactive down the group. Group 7, the halogens (such as chlorine, bromine and iodine), are reactive non-metals that become less reactive down the group. Group 0, the noble gases, are almost completely unreactive. Pupils also test oxides: when metals burn, their oxides are mostly basic, and if they dissolve they make alkaline solutions, whereas non-metals such as sulfur and carbon burn to make oxides that dissolve to make acidic solutions.

Words your child will hear

Element: A substance made of only one kind of atom, such as iron or oxygen.
Group: A vertical column in the Periodic Table. Elements in a group have similar properties.
Period: A horizontal row in the Periodic Table.
Alkali metals: The metals in Group 1, such as lithium, sodium and potassium, which react vigorously with water.
Halogens: The reactive non-metals in Group 7, such as chlorine and iodine.
Noble gases: The unreactive gases in Group 0, such as helium, neon and argon.
Atomic number: The number that gives an element’s place in the modern Periodic Table.

What the National Curriculum says

The programme of study for Key Stage 3 says:

Pupils should be taught about the varying physical and chemical properties of different elements
Pupils should be taught about the principles underpinning the Mendeleev Periodic Table
Pupils should be taught about the Periodic Table: periods and groups; metals and non-metals
Pupils should be taught about how patterns in reactions can be predicted with reference to the Periodic Table
Pupils should be taught about the properties of metals and non-metals
Pupils should be taught about the chemical properties of metal and non-metal oxides with respect to acidity

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

A worked example

Lithium reacts steadily with water, and sodium reacts faster and melts into a ball. Predict what potassium will do, and what it makes.

Notice the pattern. Lithium, sodium and potassium are all in Group 1 and sit one below another, with lithium at the top and potassium at the bottom.
Look at the trend. Lithium reacts steadily, while sodium reacts more quickly. So reactivity increases as you go down Group 1.
Predict. Potassium is below sodium, so it should react more vigorously still: it will skim about on the water, fizz rapidly, and the hydrogen it gives off will catch fire, burning with a lilac flame.
Name the products. Group 1 metals react with water to make a metal hydroxide and hydrogen.
```
potassium + water
→ potassium hydroxide + hydrogen
```
Predict the colour of universal indicator. Potassium hydroxide dissolves to make an alkaline solution, so the indicator turns blue or purple. (This reaction is shown only as a teacher demonstration behind a safety screen.)

Potassium reacts even more vigorously than sodium and makes potassium hydroxide and hydrogen. The solution is alkaline, so universal indicator turns blue or purple.

Common mistakes and how to help

Assuming all metals are hard, heavy solids

Everyday metals such as iron, copper and steel are strong and dense, so they set the pattern children expect.

What helps: Show the exceptions. Mercury is liquid at room temperature, sodium and potassium can be cut with a knife, and lithium is light enough to float on water. Properties are patterns, not rules.

Thinking element symbols are always the first letters of the English name

Most symbols such as O, C or Ca are, so Na for sodium and Fe for iron seem like mistakes.

What helps: Explain that some come from Latin names (natrium for sodium, ferrum for iron). Learning symbols in families, a group at a time, helps more than chanting them in order.

Believing that reactivity always increases going down a group

It is true for the alkali metals, so children apply the rule to every group.

What helps: Compare Group 1 with Group 7. The alkali metals get more reactive going down, but the halogens get less reactive going down, so the direction of the trend depends on the group. Always check which group you are in.

Thinking all non-metals are gases and cannot conduct electricity

Oxygen, nitrogen and chlorine are well-known non-metal gases, and non-metals are usually poor conductors.

What helps: List the different states: carbon and sulfur are solids, and bromine is a liquid. Graphite, a form of carbon, conducts electricity, which is why it is used in some electrodes and electrical contacts.

How to help at home

Metal or non-metal? Collect a dozen objects, such as a steel spoon, a plastic comb, an aluminium foil tray, a glass jar and a pencil, and sort them by their properties. Is it shiny? Does it bend? Does it feel cold? Which ones are metals, and how do you know?
Play Mendeleev. Write the names and properties of about twenty elements on cards, with one or two left blank. Ask your child to lay them out in rows so that similar elements line up, leaving gaps for the ones they would predict to be missing.
Hunt for elements around the house. Find aluminium foil, copper pipe or wire, steel nails (which are mostly iron), a helium balloon and a pencil “lead” (graphite, a form of carbon). Ask your child to find each element in the Periodic Table, say whether it is a metal or a non-metal, and name the property that makes it useful: foil bends without breaking, copper conducts electricity, and helium is light and unreactive.
Check a label. Cereal and mineral-water labels list minerals such as iron, calcium, sodium and potassium, which are present as compounds. Ask your child to find each one in the Periodic Table and say which part of the table it sits in: sodium and potassium are in Group 1, calcium is in Group 2, and iron is in the central block of metals. Point out that the label means compounds of these metals, not the shiny metals themselves.
Draw a family tree. Pick a group, such as the alkali metals or the halogens, and make a poster showing the elements in order with their properties. Your child can then explain the trend in their own words.

Leads on to

Key Stage 4: Atomic structure, isotopes and moles
Key Stage 4: The Periodic Table and group trends

Everything in Key Stage 3 science

Updated 20 October 2026.