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Matter in Chemistry

by Ron Kurtus (5 December 2016)

Since Chemistry is a study of the composition, structure, properties, and change of matter, knowledge about matter is important to you for understanding the subject.

The definition of matter is anything that occupies space and has mass. Matter can be classified according to its state or phase. Matter can also be subdivided into general categories.

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This lesson will answer those questions.

Definition of Matter

Matter is defined as anything that occupies space and has mass. You can compare the masses of substances by their densities.


Mass is the quantity of matter which a substance possesses and, depending on the gravitational force acting on it, has a unit of weight assigned to it. Although the weight then can vary, the mass of the body is a constant and can be measured by its resistance to a change of position or motion. This property of mass to resist a change of position or motion is called inertia.


Since matter does occupy space, we can compare the masses of various substances that occupy a particular unit volume. This relationship of mass to a unit volume is called the density of the substance. It can be shown in a mathematical formula:

D = m/V


States of Matter

Matter occurs in four states or phases: solid, liquid, gas, and plasma. A solid has both a definite size and shape. A liquid has a definite volume but takes the shape of the container and a gas has neither definite shape nor definite volume. The plasma state is not usually considered in chemistry.

These states of matter can often be changed by the addition of heat energy. An example of this is ice changing to liquid water and finally to steam.

Categories of Matter

Matter can be classified under general categories: elements, compounds, and mixtures. Elements and compounds are often considered distinct substances, as opposed to mixtures which are not distinct.


If a substance is made up of only one kind of atom, it is called an element. Examples of elements include: nitrogen, gold, and neon. An element is a homogeneous material since all parts are the same throughout.

Two or more atoms of the same type can bond as a molecule. Examples are the hydrogen molecule and oxygen molecule.


If a material is composed of two or more kinds of atoms joined together in a definite grouping, it is classified as a compound.

Compounds always occur in a definite composition is called the Law of Definite Composition or Proportion. An example of this is water: it always occurs a molecules with a two hydrogen atoms to one oxygen atom relationship to form the compound water.

Compounds are homogeneous and have a definite composition (Examples: water, carbon dioxide). All parts react the same. Properties of the compound are distinct and different from the properties of the individual type of elements that are combined in its make-up.


Mixtures, however, can vary in their composition. Some have indefinite composition and are generally heterogeneous (Example: marble). However, the properties of the constituents are retained. Parts of the mixture react differently to changed conditions.


Solutions are mixtures (like sugar in water) but since the substance, like sugar, is distributed evenly throughout the water, it can be said to be an homogeneous mixture.


Knowledge about matter is important for understanding Chemistry. Matter is defined as anything that occupies space and has mass. It can be classified according to its state or phase. Matter can also be subdivided into general categories.

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