A substance consisting of two or more elements chemically combined in a fixed proportion.

The smallest unit of an element that retains the properties of that element.

A pure substance that cannot be broken down into simpler substances by chemical means, made up of only one kind of atom.

A combination of two or more substances that are not chemically bonded and can be separated by physical means.

A charged particle that occurs when an atom gains or loses one or more electrons.

A group of two or more atoms bonded together, representing the smallest fundamental unit of a compound.

A type of bond that involves the sharing of electron pairs between atoms.

A substance formed when two or more elements react chemically and bond together in a fixed ratio.

A negatively charged ion formed when an atom gains one or more electrons.