What is 'Matter' ?

Definition of Matter:

Chemistry is the study of matter, which may be classified in many different ways, such as:

• State of matter (gas, liquid or solid)
• Chemical form (substance, e.g. elements and compounds, or mixtures)
• Chemical structure (atoms or molecules, etc.)

and so on.

The relationship between terms used to describe certain types of matter is summarized in the following diagram:

Examples of what is, and is not, 'matter':

Examples of things that are NOT 'matter':

Heat - You can sometimes see or sense the effects of heat, e.g. warm air rising but heat itself is a form of energy, rather than matter. Wind - Although we can sense wind or other movement of air. e.g. a draft from an ill-fitting door or window, it does not have mass so it isn't matter. Worry - There is an expression about worries "weighing on one's mind" but in reality states of mind (emotions) do not have mass or, therefore weight, and are not 'matter'. Laser beams - are sometimes visible (depending on the wavelength of the laser) and it may be possible to see particles of dust illuminated by the laser beam but the beam (column of light) itself is light, which is a form of energy, it doesn't have mass so it isn't matter.

Examples of things that are 'matter':

Air is a mixture of gases. Aluminium has mass so it is a type of matter. More specifically aluminium is a metal element Biological Cells have mass and are therefore composed of matter. That is, the atoms and molecules that together form the cell are "matter" (regardless of whether the cell is living or not). Milk is a special type of mixture called a colloid because the particles are microscopically dispersed evenly - though there are of course variations between different types of milk (e.g. from different animals and according to processing so e.g. cream may or may not be present and rise to the top over time). The screen on which you are viewing this consists of many different types of matter.

Examples of things that are NOT 'matter':

Heat - You can sometimes see or sense the effects of heat, e.g. warm air rising but heat itself is a form of energy, rather than matter. Wind - Although we can sense wind or other movement of air. e.g. a draft from an ill-fitting door or window, it does not have mass so it isn't matter. Worry - There is an expression about worries "weighing on one's mind" but in reality states of mind (emotions) do not have mass or, therefore weight, and are not 'matter'. Laser beams - are sometimes visible (depending on the wavelength of the laser) and it may be possible to see particles of dust illuminated by the laser beam but the beam (column of light) itself is light, which is a form of energy, it doesn't have mass so it isn't matter.

Although the above examples are simple, sometimes classification of something being 'matter' or not requires more thought. Here's another example:

Is a smell a form of matter?
The simple answer is "no" because 'smell' is a sensation. People and animals are more sensitive to some smells than others. However, the sensation of smell is usually due to tiny particles reaching particular nerve cells in your nose. Such small particles within the air might be atoms or molecules of gases. Atoms and molecules are matter. 'Smells' are not 'matter' but are an animal's psychophysical response to certain types of matter being present in or around its nose.

General list of categories of things that are not matter:

• Types of energy, e.g. heat, motion
• Sensations, e.g. smells
• Emotions, e.g. anger
• Time, e.g. hours, minutes

See also the page about Elements Mixtures and Compounds, and Atoms and Molecules.

Note: This is one of a series of simple pages introducing key concepts in introductory chemistry. Other pages in this section include elements, mixtures and compounds and individual pages about substances, elements, mixtures and compounds, plus pages about atoms, molecules and isotopes. If you need further information ask your chemistry tutor.