The scientific definition of a mixture is more complicated than the definition you use in everyday life. The degree of combination, the presence or lack of chemical reactions, the size of the particles and the distribution of one substance among another all determine whether something fits the scientific characterization of a mixture and what type of mixture it is.

In science, specifically in chemistry, a mixture is when you combine two or more substances and each of the substances retains its own chemical makeup. To be a mixture, the substances cannot form or break chemical bonds with each other.

In order to be considered a mixture, the substances must satisfy three general properties. The components in a mixture can easily be separated, they each keep their own chemical properties and the proportion of the components is variable.

A homogeneous mixture is one where all the substances in the mixture are distributed evenly within the entire mixture. This type of mixture can be sampled at any area and get the same composition of the substances. An example of this is salt and water. The salt dissolves in water and forms a homogeneous mixture throughout the entire container it is in.

A heterogeneous mixture is basically the opposite of a homogeneous mixture. It's a mixture of two or more items that do not produce evenly distributed substances throughout the container, even though the mixture has the same composition throughout. A good example of this is a mixed cereal or chocolate chip cookies, in which you can see different items with the naked eye.

Mixtures are classified as heterogeneous or homogeneous and further classified due to the particle size of the components or substances. These classifications are a solution, a colloid and a suspension.

A solution has tiny particles sizes that are less than 1 nanometer in diameter. Components of a solution can't be separated by centrifuging or decanting the mixture. An example of this is air.

A colloid mixture looks homogeneous without magnification, but when you see it under a microscope, you can see that it's not mixed evenly. Particle sizes of colloids are from 1 nanometer to 1 micrometer. The separate substances in a colloid can be isolated by a centrifuge. An example of a colloid is hair spray where the liquid is an aerosol that combines with a gas.

A suspension has larger particles than the above two mixtures. At times, the mixture appears heterogeneous. Suspensions have stabilizing agents to keep the particles from separating naturally from each other. Both decantation and centrifugation can separate suspensions. An example of a suspension is salad dressing with vinegar and water. The heavier substance of the oil separates and goes to the bottom of the container while the water floats on top.