1
C
Some Basic Concept
01
h ontents
apter of Chemistry
01. Introduction 3
02. Laws of Chemical Combination 8
03. Mole Concept 12
04. Empirical and molecular formula 17
05. Stoichiometry and limiting reagent 19
06. Concentration terms 24
07. Exercise-I (Conceptual Questions) 27
08. Exercise-II (Previous Year Questions) 31
09. Exercise-III (Analytical Questions) 33
NEET SYLLABUS
SOME BASIC CONCEPTS OF CHEMISTRY : General Introduction: Importance and scope of chemistry. Laws of chemical
combination, Dalton’s atomic theory: concept of elements, atoms and molecules. Atomic and molecular masses. Mole concept
and molar mass; percentage composition and empirical and molecular formula; chemical reactions, stoichiometry and
calculations based on stoichiometry.
, ALLEN Pre-Medical : Chemistry 3
SOME BASIC CONCEPTS OF CHEMISTRY
1.0 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. Can we see, weight and perceive these entities? Is it possible to count the
number of atoms and molecules in a given mass of matter and have a quantitative relationship between the
mass and number of these particles (atoms and molecules)? We will like to answer some of these questions in this
unit. We would further describe how physical properties of matter can be quantitatively described using numerical
values with suitable units.
MATTER
PHYSICAL
Solid Liquid Gas CHEMICAL
definite shape definite volume but no definite
& volume no definite shape shape & volume
Pure Substance Mixture
fixed ratio of masses
of constituents
Homogeneous Heterogeneous
Elements Compounds same composition throughout composition is
& component are indistinguishable. not uniform.
Z:\NODE02\B0B0-BA\NURTURE\CHEM\ENG\MODULE_1\1. SOME BASIC CONCEPTS OF CHEMISTRY\01THEORY.P65
eg. gases, liquid solution, alloys, eg. sand & water,
Consists of only one Made of two or more atmospheric air nearly homogeneous
type of atoms atoms of different elements
Classification of universe
Universe is classified into two types .
(1) Matter (2) Energy
MATTER : The thing which occupies space and having mass which can be felt by our five senses is called
matter.
Matter is further classified into two categories :
(I) Physical classification (II) Chemical classification
1.1 PHYSICAL CLASSIFICATION
It is based on physical state under ordinary conditions of temperature and pressure, matter can be classified into
the following three types :
(a) Solid (b) Liquid (c) Gas
(a) Solid : A substance is said to be solid if it possesses a definite volume and a definite shape.
e.g. sugar, iron, gold, wood etc.
(b) Liquid : A substance is said to be liquid if it possesses a definite volume but not definite shape. They take
up the shape of the vessel in which they are put.
e.g. water, milk, oil, mercury, alcohol etc.
E
,4 Pre-Medical : Chemistry ALLEN
(c) Gas : A substance is said to be gas if it neither possesses a definite volume nor a definite shape. This is
because they fill up the whole vessel in which they are put.
e.g. hydrogen(H2), oxygen(O2), carbon dioxide(CO2) etc.
1.2 Chemical Classification
It may be classified into two types :
(A) Pure Substance (B) Mixture
(A) Pure Substance : A material containing only one type of substance. Pure Substance can not be sepa-
rated into simpler substance by physical method.
e.g. : Element = Na, Mg, Ca .................. etc.
Compound = HCl, H2O, CO2, HNO3 .......... etc.
Pure substance is classified into two types :
(a) Element (b) Compound
(a) Element : The pure substance containing only one kind of atoms.
It is classified into 3 types (depend on physical and chemical property)
(i) Metal ® Zn, Cu, Hg, Ac, Sn, Pb etc.
(ii) Non-metal ® N2, O2, Cl2, Br2, F2, P4, S8 etc.
(iii) Metalloid ® Si, Ge, etc.
(b) Compound : It is defined as pure substance containing more than one kind of elements or atoms which
are combined together in a fixed proportion by weight and which can be decomposed into simpler
substance by the suitable chemical method. The properties of a compound are completely different from
those of its constituent element.
e.g. HCl, H2 O , H2 SO4 , HClO4 , HNO3 etc.
(B) Mixture : A material which contains more than one type of substances and which are mixed in any ratio
by weight is called as mixture. The property of the mixture is the property of its components. The
mixture can be separated by simple physical method.
Mixture is classified into two types :
(a) Homogeneous mixture : The mixture, in which all the components are present uniformly is called as
homogeneous mixture. Components of mixture are present in single phase.
e.g. Water + Salt, Water + Sugar, Water + alcohol,
Z:\NODE02\B0B0-BA\NURTURE\CHEM\ENG\MODULE_1\1. SOME BASIC CONCEPTS OF CHEMISTRY\01THEORY.P65
(b) Heterogeneous mixture : The mixture in which all the components are present non-uniformly
e.g. Water + Sand, Water + Oil, blood, petrol etc.
• These three physical states are interconvertible on changing the condition of temperature and pressure.
Illustration 1. Which is an example of matter according to physical state at room temperature and pressure?
(1) solid (2) liquid (3) gas (4) all of these
Solution (4) According to the physical state at room temperature and pressure, the matter is present in 3
states solid, liquid and gas.
Illustration 2. What are the types of the compound?
(1) Organic compounds (2) Inorganic compounds
(3) Both (1) and (2) (4) None of these
Solution (3) Compounds are divided in 2 types. Inorganic compounds and organic compounds
Illustration 3. Which of the following example of a Homogeneous mixture?
(1) Water + Alcohol (2) Water + Sand
(3) Water + Oil (4) None of these
Solution (1) Water and alcohol are completely mixed and form uniform solution.
E
, ALLEN Pre-Medical : Chemistry 5
Illustration 4. Which mixture is called as solution?
(1) Heterogeneous mixture (2) Homogeneous mixture
(3) Both (1) and (2) (4) None of these
Ans. (2) Homogeneous mixture is called as solution.
Illustration 5. Which of the following statements is/are true ?
(1) An element of a substance contains only one kind of atoms.
(2) A compound can be decomposed into its components.
(3) All homogeneous mixtures are called as solutions.
(4) All of these
Ans. (4)
Illustration 6. A pure substance can only be :-
(1) A compound (2) An element
(3) An element or a compound (4) A heterogenous mixture
Ans. (3)
Illustration 7. Which one of the following is not a mixture :
(1) Tap water (2) Distilled water (3) Salt in water (4) Oil in water
Ans. (2)
Illustration 8. Which one of the following forms part of seven basic SI units :
(1) Joule (2) Candela (3) Newton (4) Pascal
Ans. (2)
1.3 S.I. UNITS (SYSTEM OF INTERNATIONAL UNITS)
Different types of units of measurements have been in use in different parts of the world e.g. kilograms, pounds
etc. for mass ; miles, furlongs, yards etc. for distance.
To have a common system of units throughout the world. French Academy of Science, in 1791, introduced a
Z:\NODE02\B0B0-BA\NURTURE\CHEM\ENG\MODULE_1\1. SOME BASIC CONCEPTS OF CHEMISTRY\01THEORY.P65
new system of measurements called metric system in which the different units of a physical quantity are related
to each other as multiples of powers of 10, e.g. 1 km = 103 m, 1cm = 10 –2 m etc. This system of units was
found to be so convenient that scientists all over the world adopted this system for scientific data.
1.4 SEVEN BASIC UNITS
The seven basic physical quantities in the International System of Units, their symbols, the names of their units
(called the base units) and the symbols of these units are given in Table.
TABLE : SEVEN BASIC PHYSICAL QUANTITIES AND THEIR S.I. UNITS
Physical Quantity Symbol S.I. Unit Symbol
Length l metre m
Mass m kilogram kg
Time t second s
Electric current I ampere A
Temperature T kelvin K
Luminous intensity Iu candela cd
Amount of the substance n mole mol
E
C
Some Basic Concept
01
h ontents
apter of Chemistry
01. Introduction 3
02. Laws of Chemical Combination 8
03. Mole Concept 12
04. Empirical and molecular formula 17
05. Stoichiometry and limiting reagent 19
06. Concentration terms 24
07. Exercise-I (Conceptual Questions) 27
08. Exercise-II (Previous Year Questions) 31
09. Exercise-III (Analytical Questions) 33
NEET SYLLABUS
SOME BASIC CONCEPTS OF CHEMISTRY : General Introduction: Importance and scope of chemistry. Laws of chemical
combination, Dalton’s atomic theory: concept of elements, atoms and molecules. Atomic and molecular masses. Mole concept
and molar mass; percentage composition and empirical and molecular formula; chemical reactions, stoichiometry and
calculations based on stoichiometry.
, ALLEN Pre-Medical : Chemistry 3
SOME BASIC CONCEPTS OF CHEMISTRY
1.0 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. Can we see, weight and perceive these entities? Is it possible to count the
number of atoms and molecules in a given mass of matter and have a quantitative relationship between the
mass and number of these particles (atoms and molecules)? We will like to answer some of these questions in this
unit. We would further describe how physical properties of matter can be quantitatively described using numerical
values with suitable units.
MATTER
PHYSICAL
Solid Liquid Gas CHEMICAL
definite shape definite volume but no definite
& volume no definite shape shape & volume
Pure Substance Mixture
fixed ratio of masses
of constituents
Homogeneous Heterogeneous
Elements Compounds same composition throughout composition is
& component are indistinguishable. not uniform.
Z:\NODE02\B0B0-BA\NURTURE\CHEM\ENG\MODULE_1\1. SOME BASIC CONCEPTS OF CHEMISTRY\01THEORY.P65
eg. gases, liquid solution, alloys, eg. sand & water,
Consists of only one Made of two or more atmospheric air nearly homogeneous
type of atoms atoms of different elements
Classification of universe
Universe is classified into two types .
(1) Matter (2) Energy
MATTER : The thing which occupies space and having mass which can be felt by our five senses is called
matter.
Matter is further classified into two categories :
(I) Physical classification (II) Chemical classification
1.1 PHYSICAL CLASSIFICATION
It is based on physical state under ordinary conditions of temperature and pressure, matter can be classified into
the following three types :
(a) Solid (b) Liquid (c) Gas
(a) Solid : A substance is said to be solid if it possesses a definite volume and a definite shape.
e.g. sugar, iron, gold, wood etc.
(b) Liquid : A substance is said to be liquid if it possesses a definite volume but not definite shape. They take
up the shape of the vessel in which they are put.
e.g. water, milk, oil, mercury, alcohol etc.
E
,4 Pre-Medical : Chemistry ALLEN
(c) Gas : A substance is said to be gas if it neither possesses a definite volume nor a definite shape. This is
because they fill up the whole vessel in which they are put.
e.g. hydrogen(H2), oxygen(O2), carbon dioxide(CO2) etc.
1.2 Chemical Classification
It may be classified into two types :
(A) Pure Substance (B) Mixture
(A) Pure Substance : A material containing only one type of substance. Pure Substance can not be sepa-
rated into simpler substance by physical method.
e.g. : Element = Na, Mg, Ca .................. etc.
Compound = HCl, H2O, CO2, HNO3 .......... etc.
Pure substance is classified into two types :
(a) Element (b) Compound
(a) Element : The pure substance containing only one kind of atoms.
It is classified into 3 types (depend on physical and chemical property)
(i) Metal ® Zn, Cu, Hg, Ac, Sn, Pb etc.
(ii) Non-metal ® N2, O2, Cl2, Br2, F2, P4, S8 etc.
(iii) Metalloid ® Si, Ge, etc.
(b) Compound : It is defined as pure substance containing more than one kind of elements or atoms which
are combined together in a fixed proportion by weight and which can be decomposed into simpler
substance by the suitable chemical method. The properties of a compound are completely different from
those of its constituent element.
e.g. HCl, H2 O , H2 SO4 , HClO4 , HNO3 etc.
(B) Mixture : A material which contains more than one type of substances and which are mixed in any ratio
by weight is called as mixture. The property of the mixture is the property of its components. The
mixture can be separated by simple physical method.
Mixture is classified into two types :
(a) Homogeneous mixture : The mixture, in which all the components are present uniformly is called as
homogeneous mixture. Components of mixture are present in single phase.
e.g. Water + Salt, Water + Sugar, Water + alcohol,
Z:\NODE02\B0B0-BA\NURTURE\CHEM\ENG\MODULE_1\1. SOME BASIC CONCEPTS OF CHEMISTRY\01THEORY.P65
(b) Heterogeneous mixture : The mixture in which all the components are present non-uniformly
e.g. Water + Sand, Water + Oil, blood, petrol etc.
• These three physical states are interconvertible on changing the condition of temperature and pressure.
Illustration 1. Which is an example of matter according to physical state at room temperature and pressure?
(1) solid (2) liquid (3) gas (4) all of these
Solution (4) According to the physical state at room temperature and pressure, the matter is present in 3
states solid, liquid and gas.
Illustration 2. What are the types of the compound?
(1) Organic compounds (2) Inorganic compounds
(3) Both (1) and (2) (4) None of these
Solution (3) Compounds are divided in 2 types. Inorganic compounds and organic compounds
Illustration 3. Which of the following example of a Homogeneous mixture?
(1) Water + Alcohol (2) Water + Sand
(3) Water + Oil (4) None of these
Solution (1) Water and alcohol are completely mixed and form uniform solution.
E
, ALLEN Pre-Medical : Chemistry 5
Illustration 4. Which mixture is called as solution?
(1) Heterogeneous mixture (2) Homogeneous mixture
(3) Both (1) and (2) (4) None of these
Ans. (2) Homogeneous mixture is called as solution.
Illustration 5. Which of the following statements is/are true ?
(1) An element of a substance contains only one kind of atoms.
(2) A compound can be decomposed into its components.
(3) All homogeneous mixtures are called as solutions.
(4) All of these
Ans. (4)
Illustration 6. A pure substance can only be :-
(1) A compound (2) An element
(3) An element or a compound (4) A heterogenous mixture
Ans. (3)
Illustration 7. Which one of the following is not a mixture :
(1) Tap water (2) Distilled water (3) Salt in water (4) Oil in water
Ans. (2)
Illustration 8. Which one of the following forms part of seven basic SI units :
(1) Joule (2) Candela (3) Newton (4) Pascal
Ans. (2)
1.3 S.I. UNITS (SYSTEM OF INTERNATIONAL UNITS)
Different types of units of measurements have been in use in different parts of the world e.g. kilograms, pounds
etc. for mass ; miles, furlongs, yards etc. for distance.
To have a common system of units throughout the world. French Academy of Science, in 1791, introduced a
Z:\NODE02\B0B0-BA\NURTURE\CHEM\ENG\MODULE_1\1. SOME BASIC CONCEPTS OF CHEMISTRY\01THEORY.P65
new system of measurements called metric system in which the different units of a physical quantity are related
to each other as multiples of powers of 10, e.g. 1 km = 103 m, 1cm = 10 –2 m etc. This system of units was
found to be so convenient that scientists all over the world adopted this system for scientific data.
1.4 SEVEN BASIC UNITS
The seven basic physical quantities in the International System of Units, their symbols, the names of their units
(called the base units) and the symbols of these units are given in Table.
TABLE : SEVEN BASIC PHYSICAL QUANTITIES AND THEIR S.I. UNITS
Physical Quantity Symbol S.I. Unit Symbol
Length l metre m
Mass m kilogram kg
Time t second s
Electric current I ampere A
Temperature T kelvin K
Luminous intensity Iu candela cd
Amount of the substance n mole mol
E
