When two or more substances are present together but are not chemically combined with each other, it is referred to as a mixture. A mixture can exist as a solution, a suspension, or a colloid. Examples of mixtures are common salt dissolved in water, in this there is no chemical bonding between the salt molecules and molecules of water. An example of a suspension is the state achieved when pressurized gas is released in the air. There is no linkage between the gas released and the air and it will eventually settle down if it is heavier than air or rise upwards. An example of a colloid is milk. This consists of many chemical substances though none of them are chemically bonded with each other. Milk will remain in this state for a long time, until it starts to spoil or an acid is added at which point the protein separates and the liquid left is known as whey.
A compound refers to a unit formed by two or more atoms that are chemically bonded to each other. The bonding is a way by which atoms are able to achieve a stable electron configuration. Chemical bonds are broadly classified into covalent and ionic.
When a compound is formed, the new substance created has entirely different properties from those of the constituent particles. A mixture on the other hand continues to have the same properties as the substances it is composed of.