Types of Matter

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Classifying Matter

We can classify substances depending on what it consists of. All matter exists as either pure substances or mixtures. Pure substances contain only one type of chemical. Examples of pure substances are gold, salt and sugar.

There are two kinds of pure substances:

Elements are pure substances made of one type of atom only. Elements cannot be changed into simpler chemical substances.
Compounds are pure substances that contain different types of atoms bonded together. Compounds can be broken down into elements in chemical reactions.

On the other hand, mixtures are impure substances that occur when pure substances (e.g. salt and sand) are mixed together without a chemical reaction occurring.

Elements

The particles that make up everything are formed from 118 different elements, 92 of which are naturally occurring. An element is a simple chemical made up of only one type of atom. For example, pure gold is an element because it contains gold atoms only.

An element cannot be broken down chemically into simpler substances. Water can be broken down into hydrogen and oxygen gases, so it is not an element. Liquid mercury cannot be broken down into simpler substances, so it is an element.

Most of the elements are solids. Eleven are gases (hydrogen, helium, nitrogen, oxygen, fluorine, neone, chlorine etc.) and just two are liquids (mercury and bromine). Most of the elements are metals. Only 20 or so are non-metals.

Compounds

A substance may be made up of particles of only one element (e.g. a gold nugget), but most substances have particles made of two or more elements chemically combined into compounds. A compound is a substance made up of groups of atoms joined together with chemical bonds. Water, sugar and salt are common examples.

A compound is made from a chemical reaction and has different physical and chemical properties from those of the element atoms that make it up.

A compound has fixed proportions of different elements (e.g. table salt, NaCl, always has equal numbers of sodium and chlorine atoms). In the compound water (H₂O) there are always twice as many hydrogen atoms as there are oxygen ones.

The chemical name of a compound often tells you what elements it is made of.

Water, (H₂O), is an example of a compound. It is made from hydrogen and oxygen, combined. In its formula:

H is the symbol for hydrogen.
O is the symbol for oxygen.
the little number '2' below the H tells you there are 2 hydrogen atoms to each 1 oxygen atom.

In the ball and stick model below, the white spheres are hydrogen and the red sphere is oxygen.

Sulfur dioxide (SO₂) is a compound made from sulfur and oxygen, combined. The two oxygens are bonded to the sulfur.

In the ball and stick model below, the red spheres are oxygen and the yellow sphere is sulfur.

Sodium chloride (salt) is another example of a compound. Its formula is NaCl. It is made of sodium and chlorine combined. Sodium chloride has very different properties from the elements sodium (a reactive metal) and chlorine (a poisonous gas).

In the models below, the purple sphere is sodium and the green sphere is chlorine.

A compound is a chemical in which atoms of different elements are joined by chemical bonds. Table salt is a compound in which atoms of the elements sodium and chlorine are bonded together to give sodium chloride crystals.

Mixtures and Pure Substances

Most matter is found in mixtures. In mixtures, the elements and/or compounds are combined without a chemical reaction occuring to change them. A solution of seawater, can of Coke, the air we breathe, metal alloys, a bucket of mixed sand and sticks from the beach, or soil from the garden are all mixtures.

When you mix two chemicals and no reaction occurs, then you have made a mixture (e.g. of sand and sugar are combined together, the result is a mixture). The substances in a mixture retain their original properties

Sugar is sweet on its own, and when mixed with water, it is still sweet.
If sand is mixed with sugar, the sugar is still sweet and the sand will still be gritty.
Iron powder is still attracted to a magnet, even when it is mixed with sand or powdered sulfur. The iron has kept its properties.

The air we breathe is a mixture of elements, including nitrogen, oxygen and argon, and the compounds such as water vapour, carbon dioxide, and the stuff coming out of this chminey!

These properties can be used to separate the substances in the mixture! The substance making up a mixture can usually be separated using physical processes such as filtering, evaporating or distilling. For example, if water is added to a sand and salt mixture, the sand can be filtered out and dried, and the salt regained by evaporating the water.

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