CLASSIFICATION OF MATTER BASIC INFORMATION AND TUTORIALS

Matter is made up of very tiny units called atoms. Each different type of atom is the building block of a different chemical element. Presently, the International Union of Pure and Applied Chemistry (IUPAC) recognizes 112 elements, and all matter is made up of just these types! The known elements range from common substances, such as carbon, iron, and silver, to uncommon ones, such as lutetium and thulium.

About 90 of the elements can be obtained from natural sources. The remainder do not occur naturally and have been created only in laboratories. On the inside front cover you will find a complete listing of the elements and also a special tabular arrangement of the elements known as the periodic table. The periodic table is the chemist s directory of the elements.

Chemical compounds are substances comprising atoms of two or more elements joined together. Scientists have identified millions of different chemical compounds. In some cases, we can isolate a molecule of a compound.

A molecule is the smallest entity having the same proportions of the constituent atoms as does the compound as a whole. A molecule of water consists of three atoms: two hydrogen atoms joined to a single oxygen atom.

A molecule of hydrogen peroxide has two hydrogen atoms and two oxygen atoms; the two oxygen atoms are joined together and one hydrogen atom is attached to each oxygen atom. By contrast, a molecule of the blood protein gamma globulin is made up of 19,996 atoms, but they are of just four types: carbon, hydrogen, oxygen, and nitrogen.


The composition and properties of an element or a compound are uniform throughout a given sample and from one sample to another. Elements and compounds are called substances. (In the chemical sense, the term substance should be used only for elements and compounds.)

A mixture of substances can vary in composition and properties from one sample to another. One that is uniform in composition and properties throughout is said to be a homogeneous mixture or a solution. A given solution of sucrose (cane sugar) in water is uniformly sweet throughout the solution, but the sweetness of another sucrose solution may be rather different if the sugar and water are present in different proportions.

Ordinary air is a homogeneous mixture of several gases, principally the elements nitrogen and oxygen. Seawater is a solution of the compounds water, sodium chloride (salt), and a host of others.

Gasoline is a homogeneous mixture or solution of dozens of compounds.

In heterogeneous mixtures sand and water, for example the components separate into distinct regions. Thus, the composition and physical properties vary from one part of the mixture to another. Salad dressing, a slab of concrete, and the leaf of a plant are all heterogeneous. It is usually easy to distinguish heterogeneous from homogeneous mixtures.