What is a compound in the context of matter?

A compound, in the context of matter, refers specifically to a substance that is made up of two or more different kinds of atoms that are chemically combined in a fixed ratio. This means that when elements combine to form a compound, they create a new substance with its own unique properties that differ from those of the individual elements. For example, water (H2O) is a compound consisting of two hydrogen atoms and one oxygen atom.

Understanding this definition helps differentiate a compound from other types of matter. A single type of atom would represent an element, not a compound. An elementary substance is also an element, while an uncombined atom is simply an atom that has not reacted with other atoms to form a compound. Therefore, identifying a compound as a substance formed from different types of atoms is crucial in distinguishing it within the broader classification of matter.