SOME BASIC CONCEPTS OF CHEMISTRY 1
UNIT 1
SOME BASIC CONCEPTS OF CHEMISTRY
d
he
Chemistry is the science of molecules and their
pu T
transformations. It is the science not so much of the one
is
hundred elements but of the infinite variety of molecules that
may be built from them ...
able to
re ER
After studying this unit, you will be
Roald Hoffmann
bl
• understand and appreciate the
role of chemistry in different
spheres of life;
• explain the characteristics of
three states of matter;
be C
Chemistry deals with the composition, structure and
• classify different substances into
elements, compounds and
properties of matter. These aspects can be best described
mixtures; and understood in terms of basic constituents of matter:
o N
• define SI base units and list some atoms and molecules. That is why chemistry is called
commonly used prefixes; the science of atoms and molecules. Can we see, weigh
• use scientific notations and and perceive these entities? Is it possible to count the
perform simple mathematical number of atoms and molecules in a given mass of matter
operations on numbers; and have a quantitative relationship between the mass and
©
• differentiate between precision and number of these particles (atoms and molecules)? We will
accuracy;
like to answer some of these questions in this Unit. We
• determine significant figures;
would further describe how physical properties of matter
• convert physical quantities from
one system of units to another;
can be quantitatively described using numerical values
• explain various laws of chemical
with suitable units.
combination; 1.1 IMPORTANCE OF CHEMISTRY
• appreciate significance of atomic
mass, average atomic mass,
Science can be viewed as a continuing human effort to
molecular mass and formula systematize knowledge for describing and understanding
tt
mass; nature. For the sake of convenience science is sub-divided
• describe the terms – mole and into various disciplines: chemistry, physics, biology,
molar mass; geology etc. Chemistry is the branch of science that studies
• calculate the mass per cent of the composition, properties and interaction of matter.
no
different elements constituting a Chemists are interested in knowing how chemical
compound;
transformations occur. Chemistry plays a central role in
• determine empirical formula and
science and is often intertwined with other branches of
molecular formula for a compound
from the given experimental data; science like physics, biology, geology etc. Chemistry also
• perform the stoichiometric plays an important role in daily life.
calculations. Chemical principles are important in diverse areas, such
as: weather patterns, functioning of brain and operation
,2 CHEMISTRY
of a computer. Chemical industries
manufacturing fertilizers, alkalis, acids, salts,
dyes, polymers, drugs, soaps, detergents,
metals, alloys and other inorganic and organic
chemicals, including new materials, contribute
in a big way to the national economy.
Chemistry plays an important role in meeting
human needs for food, health care products
d
and other materials aimed at improving the
quality of life. This is exemplified by the large
scale production of a variety of fertilizers,
he
improved varieties of pesticides and
insecticides. Similarly many life saving drugs Fig. 1.1 Arrangement of particles in solid, liquid
such as cisplatin and taxol, are effective in and gaseous state
pu T
cancer therapy and AZT (Azidothymidine)
Everything around us, for example, book, pen,
is
used for helping AIDS victims, have been
isolated from plant and animal sources or pencil, water, air, all living beings etc. are
re ER
prepared by synthetic methods. composed of matter. You know that they have
mass and they occupy space.
bl
With a better understanding of chemical
principles it has now become possible to You are also aware that matter can exist in
design and synthesize new materials having three physical states viz. solid, liquid and gas.
specific magnetic, electric and optical The constituent particles of matter in these
be C
properties. This has lead to the production of three states can be represented as shown in
superconducting ceramics, conducting Fig. 1.1. In solids, these particles are held very
polymers, optical fibres and large scale close to each other in an orderly fashion and
o N
miniaturization of solid state devices. In recent there is not much freedom of movement. In
years chemistry has tackled with a fair degree liquids, the particles are close to each other
of success some of the pressing aspects of but they can move around. However, in gases,
environmental degradation. Safer alternatives the particles are far apart as compared to those
to environmentally hazardous refrigerants like present in solid or liquid states and their
©
CFCs (chlorofluorocarbons), responsible for movement is easy and fast. Because of such
ozone depletion in the stratosphere, have been arrangement of particles, different states of
successfully synthesised. However, many big matter exhibit the following characteristics:
environmental problems continue to be (i) Solids have definite volume and definite
matters of grave concern to the chemists. One shape.
such problem is the management of the Green
House gases like methane, carbon dioxide etc. (ii) Liquids have definite volume but not the
Understanding of bio-chemical processes, use definite shape. They take the shape of the
of enzymes for large-scale production of container in which they are placed.
tt
chemicals and synthesis of new exotic (iii) Gases have neither definite volume nor
materials are some of the intellectual challenges definite shape. They completely occupy the
for the future generation of chemists. A container in which they are placed.
no
developing country like India needs talented These three states of matter are
and creative chemists for accepting such interconvertible by changing the conditions of
challenges. temperature and pressure.
1.2 NATURE OF MATTER he at
Solid ⇀
heat
liquid ⇀
Gas
↽
cool ↽
cool
You are already familiar with the term matter
from your earlier classes. Anything which has On heating a solid usually changes to a
mass and occupies space is called matter. liquid and the liquid on further heating
, SOME BASIC CONCEPTS OF CHEMISTRY 3
changes to the gaseous ( or vapour) state. In composition is variable. Copper, silver, gold,
the reverse process, a gas on cooling liquifies water, glucose are some examples of pure
to the liquid and the liquid on further cooling substances. Glucose contains carbon,
freezes to the solid. hydrogen and oxygen in a fixed ratio and thus,
At the macroscopic or bulk level, matter like all other pure substances has a fixed
composition. Also, the constituents of pure
can be classified as mixtures or pure
substances cannot be separated by simple
substances. These can be further sub-divided
physical methods.
as shown in Fig. 1.2.
d
Pure substances can be further classified
into elements and compounds. An element
consists of only one type of particles. These
he
particles may be atoms or molecules. You may
be familiar with atoms and molecules from the
previous classes; however, you will be studying
pu T
about them in detail in Unit 2. Sodium, copper,
is
silver, hydrogen, oxygen etc. are some
examples of elements. They all contain atoms
re ER of one type. However, the atoms of different
bl
elements are different in nature. Some elements
such as sodium or copper, contain single
Fig. 1.2 Classification of matter atoms held together as their constituent
particles whereas in some others, two or more
be C
Many of the substances present around atoms combine to give molecules of the
you are mixtures. For example, sugar solution element. Thus, hydrogen, nitrogen and oxygen
in water, air, tea etc., are all mixtures. A mixture gases consist of molecules in which two atoms
o N
contains two or more substances present in it combine to give their respective molecules. This
(in any ratio) which are called its components. is illustrated in Fig. 1.3.
A mixture may be homogeneous or When two or more atoms of different
heterogeneous. In a homogeneous mixture, elements combine, the molecule of a
the components completely mix with each other
©
compound is obtained. The examples of some
and its composition is uniform throughout. compounds are water, ammonia, carbon
Sugar solution, and air are thus, the examples
of homogeneous mixtures. In contrast to this,
in heterogeneous mixtures, the composition
is not uniform throughout and sometimes the
different components can be observed. For
example, the mixtures of salt and sugar, grains
and pulses along with some dirt (often stone)
pieces, are heterogeneous mixtures. You can
tt
think of many more examples of mixtures
which you come across in the daily life. It is
worthwhile to mention here that the
components of a mixture can be separated by
no
using physical methods such as simple hand
picking, filtration, crystallisation, distillation
etc.
Pure substances have characteristics
different from the mixtures. They have fixed
composition, whereas mixtures may contain
the components in any ratio and their Fig. 1.3 A representation of atoms and molecules
UNIT 1
SOME BASIC CONCEPTS OF CHEMISTRY
d
he
Chemistry is the science of molecules and their
pu T
transformations. It is the science not so much of the one
is
hundred elements but of the infinite variety of molecules that
may be built from them ...
able to
re ER
After studying this unit, you will be
Roald Hoffmann
bl
• understand and appreciate the
role of chemistry in different
spheres of life;
• explain the characteristics of
three states of matter;
be C
Chemistry deals with the composition, structure and
• classify different substances into
elements, compounds and
properties of matter. These aspects can be best described
mixtures; and understood in terms of basic constituents of matter:
o N
• define SI base units and list some atoms and molecules. That is why chemistry is called
commonly used prefixes; the science of atoms and molecules. Can we see, weigh
• use scientific notations and and perceive these entities? Is it possible to count the
perform simple mathematical number of atoms and molecules in a given mass of matter
operations on numbers; and have a quantitative relationship between the mass and
©
• differentiate between precision and number of these particles (atoms and molecules)? We will
accuracy;
like to answer some of these questions in this Unit. We
• determine significant figures;
would further describe how physical properties of matter
• convert physical quantities from
one system of units to another;
can be quantitatively described using numerical values
• explain various laws of chemical
with suitable units.
combination; 1.1 IMPORTANCE OF CHEMISTRY
• appreciate significance of atomic
mass, average atomic mass,
Science can be viewed as a continuing human effort to
molecular mass and formula systematize knowledge for describing and understanding
tt
mass; nature. For the sake of convenience science is sub-divided
• describe the terms – mole and into various disciplines: chemistry, physics, biology,
molar mass; geology etc. Chemistry is the branch of science that studies
• calculate the mass per cent of the composition, properties and interaction of matter.
no
different elements constituting a Chemists are interested in knowing how chemical
compound;
transformations occur. Chemistry plays a central role in
• determine empirical formula and
science and is often intertwined with other branches of
molecular formula for a compound
from the given experimental data; science like physics, biology, geology etc. Chemistry also
• perform the stoichiometric plays an important role in daily life.
calculations. Chemical principles are important in diverse areas, such
as: weather patterns, functioning of brain and operation
,2 CHEMISTRY
of a computer. Chemical industries
manufacturing fertilizers, alkalis, acids, salts,
dyes, polymers, drugs, soaps, detergents,
metals, alloys and other inorganic and organic
chemicals, including new materials, contribute
in a big way to the national economy.
Chemistry plays an important role in meeting
human needs for food, health care products
d
and other materials aimed at improving the
quality of life. This is exemplified by the large
scale production of a variety of fertilizers,
he
improved varieties of pesticides and
insecticides. Similarly many life saving drugs Fig. 1.1 Arrangement of particles in solid, liquid
such as cisplatin and taxol, are effective in and gaseous state
pu T
cancer therapy and AZT (Azidothymidine)
Everything around us, for example, book, pen,
is
used for helping AIDS victims, have been
isolated from plant and animal sources or pencil, water, air, all living beings etc. are
re ER
prepared by synthetic methods. composed of matter. You know that they have
mass and they occupy space.
bl
With a better understanding of chemical
principles it has now become possible to You are also aware that matter can exist in
design and synthesize new materials having three physical states viz. solid, liquid and gas.
specific magnetic, electric and optical The constituent particles of matter in these
be C
properties. This has lead to the production of three states can be represented as shown in
superconducting ceramics, conducting Fig. 1.1. In solids, these particles are held very
polymers, optical fibres and large scale close to each other in an orderly fashion and
o N
miniaturization of solid state devices. In recent there is not much freedom of movement. In
years chemistry has tackled with a fair degree liquids, the particles are close to each other
of success some of the pressing aspects of but they can move around. However, in gases,
environmental degradation. Safer alternatives the particles are far apart as compared to those
to environmentally hazardous refrigerants like present in solid or liquid states and their
©
CFCs (chlorofluorocarbons), responsible for movement is easy and fast. Because of such
ozone depletion in the stratosphere, have been arrangement of particles, different states of
successfully synthesised. However, many big matter exhibit the following characteristics:
environmental problems continue to be (i) Solids have definite volume and definite
matters of grave concern to the chemists. One shape.
such problem is the management of the Green
House gases like methane, carbon dioxide etc. (ii) Liquids have definite volume but not the
Understanding of bio-chemical processes, use definite shape. They take the shape of the
of enzymes for large-scale production of container in which they are placed.
tt
chemicals and synthesis of new exotic (iii) Gases have neither definite volume nor
materials are some of the intellectual challenges definite shape. They completely occupy the
for the future generation of chemists. A container in which they are placed.
no
developing country like India needs talented These three states of matter are
and creative chemists for accepting such interconvertible by changing the conditions of
challenges. temperature and pressure.
1.2 NATURE OF MATTER he at
Solid ⇀
heat
liquid ⇀
Gas
↽
cool ↽
cool
You are already familiar with the term matter
from your earlier classes. Anything which has On heating a solid usually changes to a
mass and occupies space is called matter. liquid and the liquid on further heating
, SOME BASIC CONCEPTS OF CHEMISTRY 3
changes to the gaseous ( or vapour) state. In composition is variable. Copper, silver, gold,
the reverse process, a gas on cooling liquifies water, glucose are some examples of pure
to the liquid and the liquid on further cooling substances. Glucose contains carbon,
freezes to the solid. hydrogen and oxygen in a fixed ratio and thus,
At the macroscopic or bulk level, matter like all other pure substances has a fixed
composition. Also, the constituents of pure
can be classified as mixtures or pure
substances cannot be separated by simple
substances. These can be further sub-divided
physical methods.
as shown in Fig. 1.2.
d
Pure substances can be further classified
into elements and compounds. An element
consists of only one type of particles. These
he
particles may be atoms or molecules. You may
be familiar with atoms and molecules from the
previous classes; however, you will be studying
pu T
about them in detail in Unit 2. Sodium, copper,
is
silver, hydrogen, oxygen etc. are some
examples of elements. They all contain atoms
re ER of one type. However, the atoms of different
bl
elements are different in nature. Some elements
such as sodium or copper, contain single
Fig. 1.2 Classification of matter atoms held together as their constituent
particles whereas in some others, two or more
be C
Many of the substances present around atoms combine to give molecules of the
you are mixtures. For example, sugar solution element. Thus, hydrogen, nitrogen and oxygen
in water, air, tea etc., are all mixtures. A mixture gases consist of molecules in which two atoms
o N
contains two or more substances present in it combine to give their respective molecules. This
(in any ratio) which are called its components. is illustrated in Fig. 1.3.
A mixture may be homogeneous or When two or more atoms of different
heterogeneous. In a homogeneous mixture, elements combine, the molecule of a
the components completely mix with each other
©
compound is obtained. The examples of some
and its composition is uniform throughout. compounds are water, ammonia, carbon
Sugar solution, and air are thus, the examples
of homogeneous mixtures. In contrast to this,
in heterogeneous mixtures, the composition
is not uniform throughout and sometimes the
different components can be observed. For
example, the mixtures of salt and sugar, grains
and pulses along with some dirt (often stone)
pieces, are heterogeneous mixtures. You can
tt
think of many more examples of mixtures
which you come across in the daily life. It is
worthwhile to mention here that the
components of a mixture can be separated by
no
using physical methods such as simple hand
picking, filtration, crystallisation, distillation
etc.
Pure substances have characteristics
different from the mixtures. They have fixed
composition, whereas mixtures may contain
the components in any ratio and their Fig. 1.3 A representation of atoms and molecules
