LECTURE NOTE - 2025 CHEMISTRY [FIRST YEAR]
CHAPTER - 01
SOME BASIC CONCEPTS OF CHEMISTRY
INTRODUCTION
Chemistry deals with the composition, structure and properties of matter. These aspects can be best
described and understood in terms of basic constituents of matter: atoms and molecules. That is why
chemistry is called the science of atoms and molecules.
IMPORTANCE OF CHEMISTRY
Chemists are interested in knowing how chemical transformations occur. Chemistry plays a central
role in science and is often intertwined with other branches of science like physics, biology, geology
etc. Chemistry also plays an important role in daily life. Many life saving drugs such as cisplatin and
taxol, are effective in cancer therapy and AZT (Azidothymidine) used for helping AIDS victims, have
been isolated from plant and animal sources or prepared by synthetic methods.
NATURE OF MATTER
Anything which has mass and occupies space is called matter. Everything around us, for example,
book, pen, pencil, water, air, all living beings etc. are composed of matter.
STATES OF MATTER
Matter can exist in three physical states viz. solid, liquid and gas. The constituent particles of matter in
these three states can be represented as
3
, STUDY CENTRE
CLASSIFICATION OF MATTER
At the macroscopic or bulk level, matter can be classified as mixtures or pure substances.
In a homogeneous mixture, the components completely mix with each other and its composition is
uniform throughout. 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.
Pure substances have characteristics different from the mixtures. They have fixed composition,
whereas mixtures may contain the components in any ratio and their composition is variable. Copper,
silver, gold, water, glucose are some examples of pure substances. Glucose contains carbon, hydrogen
and oxygen in a fixed ratio and thus, like all other pure substances has a fixed composition. Also, the
constituents of pure substances cannot be separated by simple physical methods.
Pure substances can be further classified into elements and compounds. An element consists of
only one type of particles. These particles may be atoms or molecules. Some elements such as
sodium or copper, contain single atoms held together as their constituent particles whereas in some
others, two or more atoms combine to give molecules of the element. Thus, hydrogen, nitrogen and
oxygen gases consist of molecules in which two atoms combine to give their respective molecules.
When two or more atoms of different elements combine, the molecule of a compound is obtained.
The examples of some compounds are water, ammonia, carbon dioxide, sugar etc.
4
, LECTURE NOTE - 2025 CHEMISTRY [FIRST YEAR]
The atoms of different elements are present in a compound in a fixed and definite ratio and this ratio
is characteristic of a particular compound. Also, the properties of a compound are different from those
of its constituent elements. For example, hydrogen and oxygen are gases whereas the compound
formed by their combination i.e., water is a liquid. It is interesting to note that hydrogen burns with a
pop sound and oxygen is a supporter of combustion, but water is used as a fire extinguisher.
PROPERTIES OF MATTER AND THEIR MEASUREMENT
Every substance has unique or characteristic properties. These properties can be classified into two
categories – physical properties and chemical properties.
Physical properties are those properties which can be measured or observed without changing the
identity or the composition of the substance. Some examples of physical properties are colour, odour,
melting point, boiling point, density etc. The measurement or observation of chemical properties require
a chemical change to occur. The examples of chemical properties are characteristic reactions of
different substances; these include acidity or basicity, combustibility etc.
Measurement of properties
Any quantitative observation or measurement is represented by a number followed by units in which
it is measured. For example length of a room can be represented as 6 m; here 6 is the number and m
denotes metre – the unit in which the length is measured.
Two different systems of measurement, i.e. the English System and the Metric System were being
used in different parts of the world. The metric system which originated in France in late eighteenth
century, was more convenient as it was based on the decimal system. The need of a common standard
system was being felt by the scientific community. Such a system was established in 1960 known as
SI system.
5
, STUDY CENTRE
The International system of units (SI)
The International System of Units (in French Le Systeme International d’Unités – abbreviated as SI)
was established by the 11th General Conference on Weights and Measures (CGPM from Conference
Generale des Poidset Measures). The CGPM is an inter governmental treaty organization created by
a diplomatic treaty known as Metre Convention which was signed in Paris in 1875.
Each modern industrialized country including India has a National Metrology Institute (NMI) which
maintains standards of measurements. This responsibility has been given to the National Physical
Laboratory (NPL), New Delhi.
6
CHAPTER - 01
SOME BASIC CONCEPTS OF CHEMISTRY
INTRODUCTION
Chemistry deals with the composition, structure and properties of matter. These aspects can be best
described and understood in terms of basic constituents of matter: atoms and molecules. That is why
chemistry is called the science of atoms and molecules.
IMPORTANCE OF CHEMISTRY
Chemists are interested in knowing how chemical transformations occur. Chemistry plays a central
role in science and is often intertwined with other branches of science like physics, biology, geology
etc. Chemistry also plays an important role in daily life. Many life saving drugs such as cisplatin and
taxol, are effective in cancer therapy and AZT (Azidothymidine) used for helping AIDS victims, have
been isolated from plant and animal sources or prepared by synthetic methods.
NATURE OF MATTER
Anything which has mass and occupies space is called matter. Everything around us, for example,
book, pen, pencil, water, air, all living beings etc. are composed of matter.
STATES OF MATTER
Matter can exist in three physical states viz. solid, liquid and gas. The constituent particles of matter in
these three states can be represented as
3
, STUDY CENTRE
CLASSIFICATION OF MATTER
At the macroscopic or bulk level, matter can be classified as mixtures or pure substances.
In a homogeneous mixture, the components completely mix with each other and its composition is
uniform throughout. 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.
Pure substances have characteristics different from the mixtures. They have fixed composition,
whereas mixtures may contain the components in any ratio and their composition is variable. Copper,
silver, gold, water, glucose are some examples of pure substances. Glucose contains carbon, hydrogen
and oxygen in a fixed ratio and thus, like all other pure substances has a fixed composition. Also, the
constituents of pure substances cannot be separated by simple physical methods.
Pure substances can be further classified into elements and compounds. An element consists of
only one type of particles. These particles may be atoms or molecules. Some elements such as
sodium or copper, contain single atoms held together as their constituent particles whereas in some
others, two or more atoms combine to give molecules of the element. Thus, hydrogen, nitrogen and
oxygen gases consist of molecules in which two atoms combine to give their respective molecules.
When two or more atoms of different elements combine, the molecule of a compound is obtained.
The examples of some compounds are water, ammonia, carbon dioxide, sugar etc.
4
, LECTURE NOTE - 2025 CHEMISTRY [FIRST YEAR]
The atoms of different elements are present in a compound in a fixed and definite ratio and this ratio
is characteristic of a particular compound. Also, the properties of a compound are different from those
of its constituent elements. For example, hydrogen and oxygen are gases whereas the compound
formed by their combination i.e., water is a liquid. It is interesting to note that hydrogen burns with a
pop sound and oxygen is a supporter of combustion, but water is used as a fire extinguisher.
PROPERTIES OF MATTER AND THEIR MEASUREMENT
Every substance has unique or characteristic properties. These properties can be classified into two
categories – physical properties and chemical properties.
Physical properties are those properties which can be measured or observed without changing the
identity or the composition of the substance. Some examples of physical properties are colour, odour,
melting point, boiling point, density etc. The measurement or observation of chemical properties require
a chemical change to occur. The examples of chemical properties are characteristic reactions of
different substances; these include acidity or basicity, combustibility etc.
Measurement of properties
Any quantitative observation or measurement is represented by a number followed by units in which
it is measured. For example length of a room can be represented as 6 m; here 6 is the number and m
denotes metre – the unit in which the length is measured.
Two different systems of measurement, i.e. the English System and the Metric System were being
used in different parts of the world. The metric system which originated in France in late eighteenth
century, was more convenient as it was based on the decimal system. The need of a common standard
system was being felt by the scientific community. Such a system was established in 1960 known as
SI system.
5
, STUDY CENTRE
The International system of units (SI)
The International System of Units (in French Le Systeme International d’Unités – abbreviated as SI)
was established by the 11th General Conference on Weights and Measures (CGPM from Conference
Generale des Poidset Measures). The CGPM is an inter governmental treaty organization created by
a diplomatic treaty known as Metre Convention which was signed in Paris in 1875.
Each modern industrialized country including India has a National Metrology Institute (NMI) which
maintains standards of measurements. This responsibility has been given to the National Physical
Laboratory (NPL), New Delhi.
6
