Elements, Compounds & Mixtures

A molecule consists of the same element chemically bonded, or two or more atoms of different elements. Please note that two nitrogen atoms containing nitrogen molecules move as one unit.

It can be decomposed into simpler substances (elements) by chemical methods (but not by physical methods).

There are few similarities between elements, compounds, and mixtures. At the most basic level, all three are composed of atoms. Elements and compounds are purely homogeneous materials with a constant composition throughout the process. Elements and compounds can not be physically separated into their respective constituents. Compounds and mixtures are composed of different elements or different atoms

Note: This is one of a series of simple pages that introduce important concepts of chemical entries. Other pages in this section contain pages on elements, mixtures, compounds, related substances, elements, mixtures, compounds, and atoms, molecules, isotopes. If you need more information, please consult your chemical tutor.

The concept of physical and chemical change can be used to understand the difference between mixture and compound. In a mixture, two or more substances, elements or compounds are physically combined. The nature of the mixture usually reflects the nature of the various materials. For example, salt and water become mixed when salt and water are mixed. In many cases, the mixture can be separated into its own material by physical change. For example, a mixture of tomatoes, lettuce, croutons, carrots and raisins in a salad can be divided into different materials.

A homogeneous mixture is a mixture of two or more chemicals (elements or compounds) that can not visually distinguish different components. The composition of the homogeneous mixture is constant. It is generally more difficult to separate the components of the homogeneous mixture than to separate the components of the heterogeneous mixture. Differentiating between homogeneous and heterogeneous mixtures is a matter of sampling size. On a sufficiently small scale, the sample can be as small as a single molecule, so any mixtures can be said to be heterogeneous. Indeed, regardless of how many kinds of mixtures are used, the mixture is homogeneous if the desired properties are the same.

The pure substance may be an element consisting of only one atom or a compound composed of a molecule containing two or more elements. The mixture may be uniform or non-uniform depending on the degree of mixing of the components. The homogeneous mixture has the same appearance and characteristics throughout the mixture. The heterogeneous mixture is coarser and has a detectable appearance and property change in different parts of the mixture. Pure substances consist of materials with consistent properties, and the mixture consists of two or more pure substances with different properties. Therefore, you can not separate pure substances into other substances, but you can separate them into pure substances using different properties of mixed ingredients.