Pure substances are defined as substances that are made of only one type of atom or only one type of molecule (a group of atoms bonded together). The measure of whether a substance is pure is known as purity.

the only way too see the individual parts of pure substance would be with a microscope. However in a mixture you can see the different parts and the parts are not evenly distributed. One example of this is a pizza.

Elements? A substance that cannot be decomposed into simpler substances by chemical means, and is made up of atoms all with identical number of protons.

compounds? A thing that is composed of two or more separate elements; a mixture.

you may ask what a homogeneous mixture is? A mixture which has uniform composition and properties throughout. For example, air is a homogeneous mixture of gases. A teaspoonful of table salt stirred into a glass of water also makes a homogeneous mixture.

What is a solution? A solution is a homogeneous mixture of two or more substances. A solution may exist in any phase. A solution consists of a solute and a solvent. The solute is the substance that is dissolved in the solvent.

Heterogeneous mixture? A mixture is a combination of two or more pure substances in which the original substances retain their chemical properties. In some mixtures, the initial substances cannot be detected after they have been mixed.

if you have ever shined a light through a liquid you have experienced suspension.

Then you have colloids. a homogeneous, noncrystalline substance consisting of large molecules or ultra microscopic particles of one substance dispersed through a second substance. Colloids include gels, sols, and emulsions; the particles do not settle and cannot be separated out by ordinary filtering or centrifuging like those in a suspension.

This video should help explain everything a little better.