The 118 building blocks that everything — living or not — is made from.
That second sentence is the test. Water can be broken down into hydrogen and oxygen, so water is not an element. Hydrogen cannot be broken down into anything simpler, so hydrogen is. At the particle level, an element contains only one kind of atom.
There are 118 known elements at present. Each has a chemical symbol — one or two letters, the first always a capital: O for oxygen, Na for sodium, Cl for chlorine.
All 118 are arranged in the Periodic Table of Elements. The arrangement is not alphabetical and not random — elements are placed according to their properties, so elements with similar properties end up near each other. That is why the table is useful: it lets us predict patterns in the properties of elements we have never handled.
The most basic pattern is the split into metals (on the left and in the middle) and non-metals (on the right). Click through the explorer.
Most elements are metals. Non-metals are a minority, crowded into the top right.
Hydrogen sits alone at the top — it is a non-metal but does not fit neatly into any column.
Two elements are liquids at room temperature: mercury (a metal) and bromine (a non-metal). Everything else is a solid or a gas.
Elements have very different properties — hardness, thermal conductivity, and so on — which is why different elements are chosen for different jobs.
| Object | Main element, and why it is chosen |
| Coins | Copper — hard-wearing and does not corrode quickly. |
| Pencil “lead” | Carbon (as graphite) — soft enough to leave a mark on paper. |
| Instant ice cream | Nitrogen, as a liquid at −196 °C — freezes the mixture in seconds. |
| Glowing shop signs | Neon — glows when electricity passes through it. |
| Cooking pot | Aluminium — light, conducts heat well, does not rust. |