An element is a pure substance which cannot be split up into two or more simpler substances by chemical means. Sugar is not an element as it can be broken down into carbon and water.
A compound: can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means), has properties that are different from its component elements, and always contains the same ratio of its component atoms. A compound is a substance which is made up of two or more elements chemically combined together.
A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together. a mixture: consists of two or more different elements and/or compounds NOT chemically combined . Can be homogeneous or non-homogeneous can be separated into its components by physical means , and often retains many of the properties of its components .