Chemistry Key Terms and Concepts: Definitions, Models, and Examples

Chemical change

A process that involves one or more substances changing into new substances.

Chemical property

The ability of a substance to combine with or change into one or more other substances.

Chromatography

Technique that separates the component of a mixture on the basis of the tendency of each to travel or be drawn across the surface of another material.

Compound

A combination of two or more different elements that are combined chemically.

Crystallization

Separation technique that results in the formation of pure solid particles of a substance from a solution containing the dissolved substance.

Distillation

Separation technique that is based on differences in the boiling point of the substances involved.

Element

A pure substance that cannot be separated into simpler substances by physical or chemical means.

Extensive properties

Dependent on the amount of substance present.

Filtration

A technique that uses a porous barrier to separate a solid from a liquid.

Gas

A form of matter that flows to conform to the shape of its container and fills the entire volume of its container.

Heterogeneous mixture

Does not blend smoothly throughout and in which the individual substances remain distinct.

Homogeneous mixture

Has constant composition throughout; always has a single phase.

Intensive properties

Independent of the amount of substance present.

Law of conservation of mass

Mass is neither created nor destroyed during a chemical reaction - it is conserved.

Law of definite proportions

Regardless of amount, a compound is always composed of the same elements in the same proportion by mass.

Law of multiple proportions

When different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element.

Liquid

A form of matter that flows, has constant volume, and takes the shape of its container.

Mixture

Combination of two or more pure substances in which each pure substance retains its individual chemical properties.

Percent by mass

Ratio of mass of each element to the total mass of the compound.

Periodic table

Organizes elements into a grid of horizontal rows (periods) and vertical columns (groups or families).

Physical property

Characteristic that can be observed or measured without changing the sample's composition.

Solid

Form of matter that has its own definite shape and volume.

Solution

Also known as homogeneous mixtures.

States of matter

Physical forms that classify matter on Earth.

Substance

Matter that has a uniform and unchanging composition.

Vapor

Gaseous state of a substance that is a solid or a liquid at room temperature.