Definition of matter in chemistry; the basis of the physical world

In chemistry, matter is a fundamental concept; everything around us—from the smallest particles in the air to the largest galaxies—is made of matter. To properly understand chemical phenomena, one must first know what matter is, its properties, what it is composed of, and how it changes. This article provides a comprehensive overview of the definition of matter, its various states of matter, its atomic structure, its distinction from energy, and its significance in chemistry.

Subject definition

In short, matter is anything that has mass and occupies space. This simple definition encompasses all material objects and even some immaterial ones, such as air and gases. For example, rocks, water, wood, metals, steam, and even the human body are made of matter.

In chemistry, matter is defined as a mixture of atoms and molecules . An atom is the smallest unit of matter, retaining the chemical properties of its element. A molecule consists of two or more atoms linked together by chemical bonds. For example, a water molecule (H₂O) consists of two hydrogen atoms and one oxygen atom.

Basic material properties

Matter possesses certain fundamental properties that distinguish it from other concepts such as energy:

Mass: The amount of matter contained in an object is called its mass. Mass is a measure of an object’s resistance to changes in its state of motion and is usually measured in kilograms or grams.
Volume: The space a substance occupies. For example, water in a cup fills part of this space.
Density: The ratio of mass to volume is called density. This property is very useful for distinguishing between different materials. Iron, for example, is denser than wood.
Physical states of matter: Matter can exist in different states of matter, such as solid, liquid, gaseous, and plasma. Each state has its own specific properties.
Variability: Matter can undergo physical and chemical changes. Physical changes refer to substances whose properties remain constant (e.g., melting ice), while chemical changes refer to substances whose atomic structure changes (e.g., burning wood).

Different states of matter

1. Solids

In the solid state, the particles of a substance are very close together and their movement is restricted. Therefore, solids have a constant shape and a constant volume. Examples of solids are rocks, minerals, wood, and ice.

2. Liquid

Liquid particles have greater freedom of movement than solid particles. The shape of a liquid depends on the volume of the container it is in, but its volume itself remains constant. Examples of liquids are water, oil, and alcohol.

3. Gas

In gases, the particles are far apart and move freely in a vacuum. Gases have no fixed shape or volume and are easily compressible. The most common gases include air, oxygen, and carbon dioxide.

4. Plasma

Plasma is a state of matter that exists at extremely high temperatures. In this state, atoms lose electrons and become charged particles. Plasma occurs in sunlight, lightning, and some industrial devices (such as neon lamps).

5. Bose-Einstein condensates

This rare state of matter occurs at temperatures near absolute zero. Under these conditions, atoms lose almost all of their kinetic energy and behave like a single quantum system.

Physical structure at the atomic level

All matter is made up of atoms . Atoms, in turn, consist of three basic subatomic particles:

Proton (positively charged)
Neutron (uncharged)
Electron (negatively charged)

Protons and neutrons are located in the atomic nucleus, while electrons orbit it. The structure and arrangement of these particles determine the chemical properties of each element.
Different atoms combine to form molecules or compounds . The type of bond between the atoms (ionic, covalent, or metallic) is crucial for the final properties of a substance.

The difference between matter and energy

Although matter and energy are distinct concepts, they can be used synonymously according to Einstein’s famous theory of relativity (E=mc²) . Matter possesses mass and a physical structure, while energy is characterized by its ability to do work or cause change. Heat and light, for example, are two different forms of energy that act upon matter, such as the melting of ice or the evaporation of water.

Kinko’s revised Accurate-PSG

physical changes

Changes in matter can be divided into two main categories:

Physical changes: In this type of change, the properties of matter remain constant, but its shape, state of matter, or size changes. Examples: melting ice, freezing water, fracturing rocks.
Chemical changes: This type of change alters the atomic structure of a substance and leads to the formation of new substances with different properties. Examples include the oxidation of iron , the combustion of wood, and the fermentation of sugar.

Classification of materials

Materials are generally divided into two main categories:

1. Pure substance

Materials whose composition remains constant within the sample . These materials include elements (such as oxygen, iron, and gold) and compounds (such as water, salt, and carbon dioxide).

2. Mixture

A mixture is a combination of two or more substances without a chemical reaction. Mixtures are divided into two categories:

Homogeneous (solution): The components are evenly distributed (e.g., water and sugar).
Heterogeneous: Its components are clearly recognizable (e.g., sand in water or lettuce).

Understanding the importance of matter in chemistry

Understanding the nature of matter is the foundation of all areas of chemistry. A comprehensive understanding of the properties and structure of matter enables us to predict chemical reactions, develop new materials, and realize numerous industrial, pharmaceutical, and environmental applications.
For example:

Organic chemistry is the study of compounds that contain carbon (organic materials).
Inorganic chemistry deals with materials that do not contain carbon, such as metals and salts.
Physical chemistry investigates the relationship between the structure of matter and energy.
Analytical chemistry uses various methods to identify and measure substances.

In conclusion

Matter is therefore a fundamental concept in chemistry and physics. Everything around us consists of matter, which exists in various states of matter, such as solids, liquids, gases, and plasma. Understanding the structure, properties, and changes of matter is essential for a deeper understanding of natural phenomena and modern technologies.
This understanding forms the basis not only of chemistry but of all experimental sciences.