• Written By Shalini Kaveripakam

# Nature of Matter: Classification and its Properties

We know that the universe is made up of matter and energy. Humans are constantly trying to discover the relationship between energy and matter and their interactions in day-to-day life. To understand this relationship, we need to know more about the nature of matter. Matter existed on the earth even before the first man had appeared on it. Do you understand that all substances present around us can be classified as matter? What is this matter?

## What is Nature of Matter?

Everything around us and the presence of which can be felt with the help of any of our five senses, i.e., sight, touch, smell, hearing and taste, is called matter. This whole universe is made up of only two things, viz. matter and energy. Experiments have shown that all types of matter possess mass and occupy space. Hence, matter is defined as anything that occupies space, possesses mass and the presence of which can be felt by any one or more of our five senses.

The examples of matter are innumerable. These include clothes, iron, gold, plastics, wood, water, milk, petrol, kerosene oil, air, etc.

### Classification of Matter

There are two ways of classifying matter:

(A) Physical nature of matter

(B) Chemical Classification.

#### (A) Physical Nature of Matter

Matter is classified into the following three types based on the physical state under ordinary conditions of temperature and pressure:

1. Solid-State
Solids are known for their hardness and rigid nature, which has a definite shape and definite volume. The essential characteristics of the solid state are:
1. Solids have definite shape and volume.
2. Solids are generally rigid.  If some solids (such as rubber) change their shape on the external force, it regains its shape to remove the force.
3. Solid can have any number of free surfaces.
4. The intermolecular spaces are tiny.
5. The intermolecular forces are enormous.
6. The dimensions of solids do not increase in large proportion on heating or cooling.
7. When two solids are kept in contact with one another, they do not mix, and they do not diffuse.
8. The density of solids is generally high. Mass occupied by a solid per unit volume is obtained by dividing the mass of the particular solid by the volume occupied by that mass of the solid.
9. Solid can be hardly compressed by applying pressure.
Examples of solids are rocks, stones, wood, sand, metals like iron, copper, nickel, etc.
2. Liquid State
A liquid state is a state of matter with a definite mass and volume but no definite shape. The characteristics of the liquid state of a substance are as follows:
1. Liquid has definite mass and volume.
2. Liquids do not have a definite shape but take the shape of the container vessel.
3. The force of attraction between molecules of the liquid is less than that of solids. Thus, liquids can flow.
4. Intermolecular spaces in liquids are more extensive than in solids. Thus, liquids are slightly more compressible than solids.
5. Liquids have only one free surface.
6. The density of the liquid is relatively less than that of solids.
7. Liquids expand far more than solids on heating and contract far more on cooling.
8. The particles of two different liquids can diffuse in one another, depending upon the nature of molecules of liquids.
Example: Milk and water particles diffuse in one another, but oil and water particles do not.
9. Liquids have fluidity and not rigidity.
Example: Water, milk, kerosene, petrol, alcohol are the examples of the substance which exist in the liquid state.
3. The Gaseous State
Out of the three states of matter, the interparticle spaces are the maximum in the gaseous state. It is because the interparticle forces which hold the different particles in the gaseous state together are minimum. As a result, rigidity is the minimum while fluidity is the maximum.
Gas is a state of matter with a definite mass but no definite shape and no definite volume. The essential properties of this state of matter are
1. A gas contained in a vessel has a definite mass.
2.  A gas can occupy the entire space of a given vessel in which it is enclosed.
3. Intermolecular space is very, very large as compared to solids and liquids. It is due to this reason that gases are highly compressible.
4. Intermolecular forces are negligible. It is due to this reason that they can fill the entire space.
5. Gases have no free surface.
6. Gases expand to a large extent when heated, and contract to a large extent when cooled.
7. The gases diffuse in one another rapidly to form a homogeneous mixture. It is on account of large intermolecular spaces.
8. The density of the gases is minimal as compared to solids and liquids.
9. The gas particles have negligible volume and are highly compressible.
10. The kinetic energy of the particles in the gaseous state is very high.
11. Gases exert pressure.
Example: Air is a common example of a gaseous state. It is a mixture of several gases like nitrogen, oxygen, carbon dioxide, etc. A few other examples are hydrogen, ammonia, and sulphur dioxide.

The three states of matter are interconvertible by changing the conditions of pressure and temperature.

$${\rm{Solid}} \leftrightarrow {\rm{Liquid}} \leftrightarrow {\rm{Gas}}$$

Consider a block of ice at $${\rm{0}}{}^{\rm{o}}{\rm{C}}$$ placed in a beaker and heated. It changes to liquid water. Heat the water till it boils. It slowly gets converted to vapour (gas). From this observation, it is clear that the solids convert into liquids and convert to gas when they are heated. A gas on cooling liquefies to the liquid, and the liquid on further cooling freezes to the solid in the reverse process.

#### Differences Between Gas and Vapour

Gases: Substances that ordinarily exist in the gaseous state at room temperature. It is a state of matter.

Example- Hydrogen, nitrogen, and oxygen.

Vapour: Substance that ordinary exists in a solid or liquid state but changes into a gaseous state under specific conditions. Therefore, it is not a state of matter.

Example- Water vapour, mercury vapour and iodine vapour. Water and mercury ordinarily exist in the liquid state and iodine in the solid state.

#### (B) Chemical Classification of Matter

Matter can also be classified chemically. For example, matter can be classified into pure substances (an element or compound) or impure substances, which can also be termed a mixture of various substances.

Pure Substances

A pure substance is a homogeneous (same kind) material with a definite invariable (that is unchangeable) chemical composition and definite, invariable physical and chemical properties.

Characteristics of Pure Substances

1. A pure substance is essentially homogeneous.
2. A pure substance should have the same chemical composition throughout its mass.
3. It should have the same chemical properties throughout its mass.
4. A pure substance has a fixed composition.
5. A pure substance can be either an element or a compound.
Pure substances are again two types:
1. Element
2. Compound

Element: An element is defined as a pure substance that contains only one kind of particles. These particles may be atoms or molecules.

Carbon, sulphur, iron, lead, gold, mercury, hydrogen, oxygen and nitrogen are examples of familiar elements. Thus, whereas iron, gold, and copper contain single atoms as constituent particles held together, in some other cases, the constituent particles are molecules that contain two or more atoms combined. For example, hydrogen, oxygen, and nitrogen consist of molecules comprising of two atoms combined.

Atom: An atom is the smallest particle of an element that takes part in a chemical reaction. An element is made up of the same kind of atoms.

Molecule: The smallest particle of an element or compound with an independent existence and can retain all the properties is called a molecule.

Types of elements: Depending upon the physical and chemical properties, the elements are further subdivided into three classes; metals, non-metals and metalloids.

Metals are those elements that reflect light and hence possess lustre. Moreover, they are good conductors of heat and electricity, malleable (i.e., hammered to form sheets) and ductile (i.e., can be drawn into wires), exist as solids at room temperature (except mercury) and possess high density. Some common metals are copper, silver, gold, aluminium, iron, lead, tin, nickel, chromium, and mercury.

Non-metals do not reflect light and hence do not possess lustre (the only exception being iodine). Further, they are brittle, poor conductors of heat and electricity (except graphite), and exist in all three states. For example, sulphur, phosphorus, and iodine are solids, whereas bromine is a liquid. At the same time, oxygen, nitrogen, and chlorine are gases.

Metalloids are those elements that possess the characteristics of both, i.e., metals as well as non-metals. Some examples of metalloids are arsenic, antimony, and selenium

Compound: A compound is a pure substance containing two or more elements combined in a fixed proportion by mass and can be decomposed into its constituent elements by suitable chemical methods. Further, the properties of a compound are entirely different from those of its constituent elements.

Water, for example, is a compound containing hydrogen and oxygen combined in a fixed proportion of $$1:8$$ by weight. It can be decomposed into its constituent elements, i.e., hydrogen and oxygen, by passing electricity through water (after acidifying it to make it a good conductor of electricity). Further, the properties of water are entirely different from its constituents, hydrogen and oxygen. For example, hydrogen is a combustible gas, and oxygen gas is a supporter of combustion. In contrast, water is neither combustible nor a supporter of combustion but extinguishes fire. A few other common examples of compounds are carbon dioxide, sulphur dioxide, sulphuric acid, nitric acid, hydrochloric acid, caustic soda, washing soda, baking soda, common salt, copper sulphate, and nitre.

Types of Compounds. All the compounds may be divided into the following two categories.

1. Organic compounds: Organic compounds contain carbon and a few other elements like hydrogen, oxygen, nitrogen, sulphur, and halogens. These were initially obtained only from animals and plants.
2. Inorganic compounds: Inorganic compounds contain any two or more elements out of more than $$118$$ elements known so far. These are usually obtained from minerals and rocks.

Remember that though the number of elements is limited to $$118$$ so far, the number of compounds is unlimited because, in many cases, two or more elements combine to form a compound.

#### Mixtures

A material containing two or more substances (elements or compounds) in any proportion is called a mixture. The properties of a mixture are the properties of its constituents. Further, a mixture can be separated into its constituents by simple physical methods.

Types of Mixtures. There are two types of mixtures:

1. Homogeneous mixtures: A homogeneous mixture has the same properties and characteristics in all the parts of its volume. For example, alcohol mixed with water. They can be mixed well and miscible with each other. Also, milk with water or sugar with milk. These are known as true solutions
2. Heterogeneous mixture: A mixture does not have the same properties throughout its bulk. For example, when oil and water are mixed, oil being lighter than water, forms the upper layer while water denser forms the lower layer. Therefore, they do not mix as they are immiscible. Also, sand mixed with salt is an example of a heterogeneous mixture.

### Summary

As we look at our surroundings, we see many things with different shapes, size and textures. The matter is anything that has mass and occupies space. In this article, we learnt about the physical and chemical classification of matter and its characteristics—definitions of atoms, molecules, mixtures, nature of matter elements and compounds.

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