The smallest unit of an element - a small particle that is the building block of matter.

A pure substance that consists of only one type of atom that cannot be broken down into simpler substances.

Elements that are traditionally found in pairs.

A substance containing atoms of two or more different elements connected together.

Two or more atoms that are held together and that act as a unit.

A chart of the elements arranged into rows and columns according to their physical and  chemical properties.

One or two letters that represent an element.

A group of chemical symbols and numbers that represent the elements and the number of atoms of each element that make up a compound.

A characteristic of matter that can be observed or measured without changing the identity of the matter.

A change in the size, shape, form, or state of matter that does not change the matter’s identity.

To form a solution by mixing evenly.

Particles are tightly packed and fixed in place.

Particles are close but can move and flow.

Particles are far apart and move freely.

The total energy of a substance - the energy associated with the random motion of particles (atoms, molecules, or ions) in a substance.

A change in matter in which the substances that make up the matter change into other substances with different chemical and physical properties.

A solid that sometimes forms when two liquids combine - a solid that forms and separates from a liquid solution during a chemical reaction.