Compounds

The idea

Compounds are formed when different elements combine chemically to form something entirely new; their constituent elements cannot be separated by any physical method.

Hydrogen and oxygen

Hydrogen and oxygen are elements. Water is made of them.

Can we separate hydrogen from oxygen in water by a physical method?

• No, they are tightly joined
• Yes, by filtering
• Yes, by picking them out

Make a compound

Press Next step.

What is a compound

In water, the particles of hydrogen and oxygen are so tightly attached that it is generally impossible to separate them by physical methods. So water is a compound.

Compounds form when different elements combine chemically to give something entirely new. Their elements cannot be separated by any physical method.

Notes

A compound is made when different elements combine chemically.

Check yourself

A compound is formed when …

The elements in a compound can be separated by …

Water is a compound because …

A compound is …

• different elements are only mixed. Mixing makes a mixture. A compound needs a chemical combination.
• different elements combine chemically — correct. Yes!
• one element is cut in pieces. A compound has different elements.
• filtering. They cannot be separated by physical methods.
• picking by hand. They cannot be separated physically.
• no physical method — correct. Yes!
• hydrogen and oxygen are tightly attached and cannot be separated physically — correct. Yes!
• it is a liquid. Being a liquid does not make a compound.
• it has only one kind of atom. Water has atoms of two different elements.
• the same as its elements. A compound is something entirely new.
• something entirely new, made from elements — correct. Yes!
• a mixture of elements. The elements are chemically combined, not just mixed.