(1) The properties of the constituent elements of the compound no longer remain in a single state; the mixture has no fixed properties and each substance maintains its original properties (eg, no fixed melting, boiling point).
(2) The compound elements must be separated by chemical methods;
(3) The composition of the compound is usually constant. The mixture is made up of a mixture of different substances. It does not have a certain composition and cannot be represented by a chemical formula.