A pure substance made from more than one type of element chemically bonded together. Elements bond in fixed ratios and so can be represented by a chemical formula. For example, sodium chloride has the ...

The formula H₂O shows that water is made from two atoms of hydrogen (H) bonded to one atom of oxygen (O). Katie: Time for some science. And today it's a chemistry classic, the periodic table. And here ...

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the ...

A chemical element is one of those squares on the periodic table that adorns many a classroom wall. Sure. But what is an element really? It is a more subtle question that you might realise. To get to ...