What is matter | States of Matter | Classification of Matter

Matter is anything that has mass and occupies space such as atoms, protons, compounds, tree, house, table, computer, etc. So, as per the definition of matter, light, heat, and radiations are not matter. So, we can say that everything in the universe that has mass and occupies space and the presence of which can be felt by any of our senses is matter.

A matter consists of particles such as atoms or elements. The constituting particles of a particular matter have specific chemical and physical properties, so they cannot be broken down into any other substance. For example, a bar of the gold element is made of gold atoms (particles). There are 118 elements out of which 92 elements are found naturally and the rest of the elements are created in laboratories and they are unstable.

Physical classification of matter (Physical Forms)

It means based on the physical state or properties under normal conditions of temperature and pressure, we can classify the matter into three states which are solids, liquids and gases. For example, the things that we see around us exist in three different states such as chair is in the solid-state, the water in a glass is in the liquid state and the oxygen that we inhale is present in the gaseous state. So, physically matter exists in three different states in nature. Each state has its own unique physical properties. The three physical states of matter are described below;

States of Matter I Physical forms

i) Solids

In this state of matter, a substance possesses definite volume and a definite shape. We can say that a substance with fixed volume and shape is called a solid. For example, iron, gold, wood, sugar, etc.

In this state of matter, the constituting particles of a substance are very close to each other as there are strong intermolecular forces between the particles and space between the particles is also very less or negligible.

Characteristic features or physical properties of solids are as follows:

• The particles remain fixed at their positions as they do not have enough energy to move. We can say that the thermal energy is very less which can make particles vibrate at their positions.
• The particles in solids are packed in a regular pattern and have very little free space between them. So, they do not move past one another.
• The density is high in the solid-state as compared to the same amount of substance in other states such as ice and water.
• Solids may be crystalline or amorphous and they are usually hard and incompressible such as wood, metal, stone, etc.
• Solids have definite shape and volume as their particles vibrate around a fixed axis.
• Due to the close tight packing and the strong intermolecular forces, the intermolecular distance between constituent particles in a matter in the solid state is short. For example, the intermolecular distance in a solid is around 0.3 x 10^-9

ii) Liquids

In this state of matter, a substance has a definite volume but its shape is not fixed. We can say that a substance is said to be a liquid if its volume is fixed but the shape is not fixed. For example, water, milk, mercury, alcohol, etc.

The constituent particles are less tightly packed as compared to solids. It is the intermediate state between solid and gas. The characteristic feature or physical properties of liquids are given below;

• The intermolecular force of attraction between particles is less as compared to solids.
• The intermolecular space in liquids is more than solids, so, particles in liquids are more free to move and do not remain fixed.
• They have fixed volume but their shape is not fixed as they can take the shape of the container in which they are stored. For example, tea, water, coffee, blood, etc.
• The rate of diffusion is also higher as compared to solids.
• They are difficult to compress due to the less space available between the particles.
• They tend to flow from the higher level to the lower level.
• Liquids change to a vapour or gaseous state on heating or when their temperature is increased.

iii) Gases

In this state of matter, a substance neither possesses a definite shape nor a definite volume. We can say that a substance is said to be a gas if it does not a have definite volume and shape.

In the gaseous state, the particles are far apart from each other and tend to occupy the whole container in which they are placed. For example, hydrogen gas (H₂), Oxygen (O₂), Carbon dioxide (CO₂), Nitrogen gas (N₂), and more.

The main properties of gases are as follows;

• They are highly compressible or easy to compress as the space between their constituent particles is very large.
• The intermolecular force of attraction is very weak so gases tend to expand to fill the container in which they are stored. They tend to occupy the entire available space.
• They occupy more space than the liquids or solids from which they are produced.
• They don't have a fixed shape and volume.
• The kinetic energy of particles is very high. They move fast and collide with each other and thus tend to spread out until they are uniformly distributed throughout the given volume such as a container.
• Their density is very low as compared to solids and liquids.
• They have two specific heats which are specific heat at constant pressure and constant volume.
• They have low viscosity.
• The molecules of a gas or a substance in the gaseous state remain in a constant random motion.
• Gases tend to diffuse with each other even if they have different densities.
• Gases apply pressure on the inner surface of a container in which it is kept.

Chemical classification of matter

As per the chemical classification, the matter is classified into two types; pure substance and mixture.

1) Pure Substance

As the name suggests, it is made of only one type of particles, which means all the constituting particles are identical in a pure substance. The constituting particles of a pure substance cannot be separated or broken into simple substances by physical method. For example, we cannot separate oxygen and hydrogen from water by physical method. Although, it can be done by using chemical methods.

A pure substance can be found only in two forms either in the form of elements or in the form of compounds. So, we can say that a pure substance is further divided into two types that include elements and compounds and are described below;

i) Element

It is the simplest form of a pure substance that is made of the identical or same type of constituting particles or atoms. It has specific physical and chemical properties and it cannot be broken into any other simple substance and cannot be built from any other simple substance. For example, hydrogen element will contain only hydrogen atoms, helium element will contain only helium atoms, and so on. This is the reason that element is considered a pure substance as it is made of the same type of atoms. Element is further divided into three types depending on their physical and chemical properties. Metals, Non-Metal and Metalloids, etc.

ii) Compound

A compound is also considered a pure substance although it is made of more than one type of elements or atoms. The reason for this is that in a compound the different atoms or elements are combined in a fixed proportion by weight to form molecules. We can say that compounds are made of identical particles that are called molecules, which contain specific atoms in a specific proportion.

For example, water is made of water molecules and each water molecule is made of two hydrogen atoms and one oxygen atom. Besides this, the properties of compounds are different from their constituent elements. Compounds can be broken into simpler substances by using appropriate chemical methods. Some common examples of compounds are HCl, H₂O, and H₂SO₄.

As the same type of molecules combines to form compounds. So, we call compounds pure substance. On the other hand, if there are different molecules that form a substance, we cannot call it a compound, in that case, it is known as a mixture.

Molecules in a compound may be physically attracted towards each other but they do not react chemically just like atoms in elements don't react with each other although they have a physical force of attraction between them. However, the atoms in a molecule definitely react with each other and form chemical bonds. For example, the chemical bond between oxygen and hydrogen in a water molecule.

2) Mixture

A material that contains or made of two or more substances, which are mixed in any ratio by weight and which are not reacting with each other chemically, is called a mixture. It can be a solid, liquid or gas. For example, a metal alloy such as steel that is made of iron and carbon is a mixture of iron and carbon. The air that we inhale is also a mixture of gases such as oxygen, nitrogen, carbon dioxide, etc. Similarly, sea water is a mixture of salt and water.

Properties of mixtures

• A mixture is made of two or more different components.
• It can be homogeneous or heterogeneous. For example, water and salt when mixed form a homogeneous mixture. Whereas, sand and sugar form a heterogeneous mixture.
• The composition of a mixture is variable, for example, 100 ml of saltwater can have 5 gram salt in it or can have 50 gram salt in it. So, the components of a mixture can be present in any proportion by mass. For example, we can mix any amount of sand and salt to make a mixture of sand and salt.
• A mixture cannot have a definite formula as it has a variable composition.
• A mixture does not have a definite boiling or melting point as the composition of its components is not fixed.
• Its properties are the same as that of its constituent particles. So, it shows all the properties of components.
• You don't need special methods or chemical reactions to form a mixture.
• The components of a mixture can be separated by simple physical methods such as filtration, sublimation, evaporation, or by using magnets, solvents, etc. for example, by using a magnet you can separate iron filings from the mixture of iron filings and sulphur. Similarly, you can remove water from saltwater through evaporation by heating the saltwater.

Mixtures are further divided into two types, homogenous mixtures and heterogeneous mixtures.

i) Homogenous mixture

As the name suggests, a mixture in which a substance is uniformly mixed or distributed into another substance is called a homogenous mixture. They are also known as solutions.

At the macro level, you cannot see any differences in the homogenous mixture as it looks consistent from all angles and there is no boundary of separation between different components as the components are present in a single phase. Such as steel, a mixture of iron and carbon contains both iron and carbon in the solid phase. In steel, you cannot see the iron and carbon separately but at the micro-level, you can see different metals are mixed to form the alloy. So, you can see the only one phase in a homogeneous mixture such as sugar in water will have only a liquid phase after sugar dissolves completely in water to form a homogenous mixture.

A homogenous mixture has the same properties and combination of its constituting particles throughout their mass. Some examples of homogenous mixtures are as follows;

• Salt in water
• Alcohol in water
• Alloys such as steel (a mixture of iron and carbon), brass, etc.
• Coffee, blood, Vinegar, Wine, etc.

Properties of homogenous mixtures:

• They have a uniform composition which means their components are distributed uniformly throughout the mixture.
• Different samples of a homogenous mixture are the same and have similar composition and properties.
• The boundary of separation between different components cannot be seen.
• It has only one phase of matter, which can be a solid, liquid or gas phase.
• They are generally known as solutions.
• The components retain their chemical identity. However, they cannot be seen separately with the naked eye or by using a microscope.
• Their components cannot be separated by mechanical methods like filtration. However, they can be separated by other methods like evaporation, sublimation, etc.

ii) Heterogeneous Mixture

A mixture that has a non-uniform composition or in which the components are not mixed or distributed uniformly is called a heterogeneous mixture. In this mixture, the composition of components vary from one part of the mixture to another part and the components can be seen separately. So, samples taken from different parts have different proportions of components.

Examples of heterogeneous mixtures:

• Cereal in milk, as it consists of solid cereal in liquid milk.
• Oil mixed in water creates a heterogeneous mixture.
• Orange juice that contains the pulp.
• Sand in water. It has two phases that can be separated easily.
• Concrete that contains cement, sand, water and gravel.
• Dry fruit chocolate as you may get different number and types of dry fruits with each bite. Similarly, sandwich, paneer pizza are also heterogeneous mixtures.
• Ice cubes in soda, where ice and soda are two different phases of matter; solid and liquid.
• Vegetable soup as each spoonful of soup will have a different amount of vegetables and other components.
• Smog as it is a collection of pollutants that are not uniformly spread out in the air and varies from one part of the atmosphere to the other part.

Properties of heterogeneous mixtures

• They have a non-uniform composition of their components.
• They may have two or more phases such as oil in water forms two separate layers each of which is called a phase, similarly, solid in liquid (suspension), gas in liquid (aerosol) have different phases.
• The components retain their chemical identity as although they are mixed, they are separate physically.
• The samples taken from different parts have a different composition.
• Their components can be separated generally.
• The boundary of separation can be seen separating the different components.

Difference between a homogeneous mixture and a heterogeneous mixture