All around us, and in the rocks

Elements, compounds and mixtures are everywhere. Air is a mixture of gases such as oxygen, nitrogen and carbon dioxide. Water is a compound of hydrogen and oxygen. Elements such as iron and aluminium build bridges, buildings and vehicles.

Knowing them is the key to invention. Chemists study how elements combine into compounds to make medicines, vaccines and fertilisers that help feed a growing population.

Engineers design materials with the properties they need. Stainless steel is an alloy stronger and longer-lasting than pure iron. Wood, steel and concrete are all mixtures. Graphene aerogel, made from carbon, is said to be the lightest material on Earth (a blade of grass can hold it up!) and is so full of tiny holes that it may be used to soak up oil spills at sea and on land.

Most rocks are mixtures of minerals, which you can see with your eyes, a magnifying glass or a microscope.

Many everyday things come from minerals: cement is made from calcite, quartz, alumina and iron oxide; talcum powder from the mineral talc.

Elements and compounds are the building blocks of matter: everything that has mass and takes up space. But not everything is matter. Light, heat, electricity, and even thoughts and feelings, are part of our world but aren't made of matter.

The Dhokra craft of Bihar and Odisha uses these ideas: a design is made in beeswax and covered in clay, the wax is melted out, and the hollow is filled with molten brass or bronze.