WHAT IS MATTER?
The matter is anything that has mass and occupies space. All solids, liquids, and gases around us are made of matter. Scientists believe that matter is made of tiny particles that clump together. You cannot see these particles but you can see the matter, for example, a book, a car, a letter, a handset, a piece of wood, a tree, a bag, etc. Think and add a few more examples from your day to day life.
When we say the matter has mass it means the matter has weight: the heavier an object, the more mass it has. Matter occupies space it means the matter has volume.
A substance is a pure kind of matter having only one kind of constituent particle (atom or molecule). Water, iron, gold, copper, aluminum, and oxygen are examples of substances. All substances are matter but all forms of matter are not substances. You must be wondering how this is possible. Well, a substance is a pure form of matter, that is, it is the same throughout. Let us take the examples of soft drinks and soil. In what category you would put them. They are not a single substance but they are a mixture of substances. Now you will find out what is the nature of matter?
PARTICULATE NATURE OF MATTER
Human beings have been questioning the nature of matter. In ancient times there were two different views about it. One school of thought believed that if we take a piece of matter (for example stone) and break it into smaller pieces and break these smaller pieces into still smaller pieces, the process can be repeated any number of times. This would happen because the matter is continuous and its piece of any size can be broken or subdivided into smaller pieces. Greek philosophers Plato and Aristotle belong to this school of thought.
The second school of thought believed that process of subdivision of matter can be repeated only for a limited number of times. A stage would be reached when the tiny particles of matter so obtained cannot be further subdivided. They believed that all matter is composed of very tiny particles. In other words, the matter has a particulate nature. The smallest indivisible particles of matter were given the name “atom” from the Greek word “atomos” for “ indivisible“.
Indian philosopher Kanada and Greek philosophers Leucippus and Democritus belong to this school of thought. The term “atom” was coined by Democritus. Today the idea of the atom has changed since it was first proposed. The modern idea of the atom originated with John Dalton in 1803. Today we talk of two types of constituent particles-atoms and molecules. An atom is a basic unit of matter and all chemical properties of matter can be explained on its basis. Molecules are important in explaining the physical properties of matter. Details about atoms and molecules will be undertaken in Lesson No. 3. Let us learn about how to classify matter.
STATES OF MATTER
Matter can be classified in many ways. However, the following are the two main
ways of classifying the matter:
1. by the physical state of matter as a solid, liquid, or gas, and
2. by the chemical composition of matter as an element, compound, or mixture.
We shall discuss these classifications in the next section.
Let us discuss the classification of matter based on physical states. Matter can
ordinarily exist in three states – solid, liquid, and gas. These three states of matter
have different properties. Water exists in all three states namely steam or water
vapor (gas), water at room temperature (liquid), and ice (solid). This is the only
substance that exists naturally in all three states.
The characteristic properties of different states of matter depend on intermolecular
forces. The forces holding molecules together are called intermolecular
forces. Intermolecular forces (i.e. forces between the constituent molecules) try to
keep molecules together but thermal energy always tries to keep them far apart. It
is the competition between molecular interaction energy and thermal energy that
decides whether a given substance under given conditions will be a solid, liquid, or
gas. Thermal or heat energy can convert one state of matter into another state. Thus
a particular state of a matter depends on both: intermolecular force and thermal
energy which basically depends upon temperature.
Each state of matter has some characteristic properties. Now you shall learn about
these properties.
Solids
We are surrounded by innumerable solid objects. A piece of wood, a stone, a pencil,
a pen, and a computer all are examples of solids. A solid has a definite size and
shape which do not change on its own (see Fig.2.1). However, by using external
forces you can change the shape of a solid. For example, you can cut a piece of
metal into two and you can use a hammer to change its shape. Can you think of any
other way to change the shape of solids? Yes, you can. Beat it into sheets or pull
it into strings.
In solids, the constituent particles are present very close to each other and the
intermolecular forces operating between the constituent particles are very strong and
they are capable of keeping the molecules in fixed positions. This is the reason why
solids are rigid and hard. Also, solids cannot be compressed. The attractive
intermolecular forces become repulsive when atoms or molecules are forced to come
further closer. When a solid is heated there is an increase in thermal energy of the
particles which results in the conversion of the solid into a liquid. The temperature at which
this happens is the melting point of the solid.
Liquids
Water is a liquid. Mustard oil and kerosene oil are other examples of liquids. Can
you think of some more examples? A liquid has a definite volume. However, a
liquid does not have a definite shape. It takes the shape of its container. A liquid
can flow. You can pour a liquid or spill it. Can you spill a solid?
Liquids have properties intermediate between solids and gases. The intermolecular
forces in liquids are weaker than solids but stronger than gases. In liquids, the
constituent particles do not occupy a fixed position as solids, but they have freedom
of movement as in gases. In liquids, intermolecular forces are stronger than those of
gases. The constituent particles (atoms and molecules) in a liquid can break away from
each other and get attracted while approaching the other molecules. Like in solids, the intermolecular forces become repulsive when an attempt is made to bring the
molecules closer by applying pressure. This is the reason why pressure does not have
much effect on the volume of liquids.
Gases
We cannot see gases but they are all around us. We can feel the presence of air
when the wind blows. The wind is moving air and is a mixture of many gases
like oxygen, nitrogen, argon, carbon dioxide, and others. A gas occupies the
entire volume of the container irrespective of its size (see Figure 2.1). In gases,
molecules move freely because the intermolecular forces are very weak and are
unable to keep the gas molecules together in bulk. The molecules remain far apart
from each other due to weak molecular interactions. Since molecules are far away
from each other in gases, they can be brought closer when pressure is applied. This
is the reason why-gases are highly compressible. We can compress gas only up
to a certain limit. Beyond this limit repulsion between gas, molecules become very
high. Temperature also affects the volume of the gases. When the temperature increases,
the volume of the gas also increases. For example when a closed container is heated
it blasts due to a rapid increase in volume.
We are lucky that a gas can be compressed easily. If this was not the case then we
could not have obtained CNG (Compressed Natural Gas). As you might be aware
that CNG is used as a clean fuel for vehicles and you might have noticed that at
the back of several Autorikshas and buses, CNG is written. We also have our cooking
gas cylinders in the kitchen because gas (LPG) is compressible. There are many other
examples of uses based on the compressibility of gases. Can you think of some more
examples? Oxygen cylinder in hospital is another example.
The distribution of molecules in solid, liquid, and gas is shown in Fig 2.2.
Three basic states of matter, described above, are dominant on Earth but they become less relevant in other parts of the universe. You will be surprised to know that 99% of the matter in the entire universe is not a solid, a liquid, or a gas. The form of matter that is more dominant is called ‘plasma’. The Sun consists of plasma as most of the other stars do. You will learn about “plasma” in your higher classes.
Different characteristics of the three states of matter have been summarized in
Table.2.1.
There are two basic concepts in the physical world around which you can organize everything. These two basic concepts are matter and energy. Both matter and energy are related to each other by the formula E = mc2. Here E is energy, m is mass and c is the velocity of light. One of the greatest scientists of all times, Albert Einstein showed that matter can be transformed into energy, and energy can be transformed into matter. No doubt, transforming matter into energy is easy whereas transforming energy into matter is difficult.
EFFECT OF TEMPERATURE AND PRESSURE ON
STATES OF MATTER
Have you ever thought about what happens if a solid substance is heated? When heat is
supplied to a solid, it expands. This expansion is very small. In fact, after receiving
thermal energy, particles (atom/molecules) vibrate more rapidly in their position and
take up more space. If particles become more energetic on further heating they leave
their fixed positions and the solid melts. Once a solid becomes liquid it can be poured
into a container. As you learned earlier, a liquid takes the shape of the container in
which it is poured. Particles in the liquid state are free to move.
Now let us see what happens when a liquid is heated. On receiving heat (thermal
energy) a liquid is converted into a gas. This happens because the kinetic energy
of the particles becomes so high that they can overcome the intermolecular force
within the liquid. Therefore liquid is converted into a gas (vapor).
When a gas is heated, the kinetic energy of the particles increases. They move more
freely and at a much higher speed. Intermolecular distance also increases and the
volume of the gas increases if pressure is kept constant. Do you know what happens
when a balloon filled with air is brought near the fire?
A pure solid turns to liquid at a fixed temperature or in other words conversion of
a pure substance from solid to liquid takes place at one particular temperature. This
particular temperature is called the melting point of that particular solid substance.
Similarly, when the liquid cools down, it converts into a solid at a particular temperature.
This temperature is called the freezing point of that particular liquid substance. The
temperature at which a liquid boils and is converted into a gas is the boiling point of
the liquid.
ELEMENTS, COMPOUNDS, AND MIXTURES
Elements
All substances are made up of chemical elements. A chemical element is a basic form
of matter that cannot be chemically broken down into simpler substances. A chemical
element is a pure substance and it consists of one type of atom distinguished
by its atomic number. Examples of some elements are helium, carbon, iron, gold,
silver, copper, aluminum, hydrogen, oxygen, nitrogen, sulfur, copper, chlorine,
iodine, uranium, and plutonium.
Elements are the building blocks of the Universe. In total, 114 elements have been
listed so far. Out of the total 114 known elements, about 90 occur naturally on Earth
and the remaining have been synthesized artificially by nuclear reactions. Only two
elements namely hydrogen (92%) and helium (7%) make up about 99% of the total
mass of the Universe. The remaining elements contribute only 1% to the total mass
of the Universe.
Out of about 90 elements found naturally on Earth, two elements silicon and oxygen
together make up almost three-quarters of the Earth’s crust. Our body is also
composed of elements but the composition of elements in the human body is very much
different from that of the Earth’s crust, as can be seen from Table 2.2.
Although human beings and Earth share elements in their composition, human beings
have several advantages like being able to think, feel, etc. Don’t you think that it is
our responsibility to take care of Earth?
Compounds
A compound is a substance formed when two or more two elements are
chemically combined. A compound can be defined as a pure substance made
from two or more elements chemically combined together in a definite
proportion by mass. When elements join to form compounds they lose their
individual properties. Compounds have different properties from the elements they
are made of. For example, water (a compound) is made up of elements – hydrogen
and oxygen but the properties of water are different from those of hydrogen and oxygen
.The world of compounds is really fascinating because compounds show a great
variety in forms and properties.
Some examples of compounds are given below:
Glucose Glycerol Calcium oxide
Sodium chloride Sulphuric acid Carbon dioxide
Hydrochloric acid Chloroform Acetic acid
Sodium carbonate Ethanol Carbon monoxide
Phenol Citric acid Methane
A pictorial representation of element compound and the mixture is shown in Fig. 2.6
Fig. 2.6: A Pictorial representation of elements, compounds, and mixtures. From the
figure we can see that elements combine to form compounds but in the mixture the
elements and compounds maintain their separate identities
Mixture
In our everyday life, we deal with a large number of substances but the majority of them
are not pure substances (elements or compounds). They are mixtures of two or more
pure substances. In the next section, we shall see that there are two types of the mixture
depending on whether the parts of the mixtures completely mix or not
The relationship among elements, compounds, and other categories of matter are
summarized in Fig. 2.7.
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