A compound is different from a mixture because a compound

Compound: A substance that is made up of more than one type of atom bonded together.

Mixture: A combination of two or more elements or compounds which have not reacted to bond together; each part in the mixture retains its own properties.

Explanation:

The different substances in a mixture are not chemically combined, whereas the different elements in a compound are. The atoms do not combine in the mixture, but they combine when they form a compound.