Summary of Chapter 1 Chemistry of class 11

2. •Chemistry is called the science of atoms and molecules.
•Chemistry is the branch of science that studies the composition, properties and
interaction in knowing how chemical transformation occur.
• It plays an important role in daily human needs for food, health care products
and other materials aimed at improving the quality of life.
• Manufacture of life saving drugs and safer alternatives to environmentally
hazardous refrigerants are its fair degree of success.

3. Anything which has mass and occupies space is called matter.
States of Matter
Solid
(Definite
volume and
definite shape)
Liquid
(Definite
volume but not
definite shape)
Gaseous
(Neither
definite volume
nor definite
shape)
Solid ⇌ Liquid ⇌ Gas
heat heat
cool cool

4. Matter
Mixtures
(a substance made by mixing
different particles)
Homogenous
Mixture
(the components are
completely mix with each
other and its composition
is uniform throughout.)
Heterogeneous
Mixture
(the composition is not
uniform throughout and
sometimes the different
component scan be
observed.)
Pure substances
(substances made up of only kind of particles
and have fixed or constant structure.)
Compounds
(two or more atoms of
different elements
combine to form the
molecule of the
compound)
Elements
(Its consist only one type
of particles i.e. atoms or
molecules. Two or more
atoms combine to form
molecules of the element.)

5. Carbon Dioxide Molecule (CO ₂) Water Molecule (H ₂O)

6. •Physical Properties: properties which can be measured
or observed without changing the identity or composition
of the substances.
•Eg. : color, odour, etc.
•Chemical Properties: properties which can be
measured or observed when a chemical change occur.
•Eg. : acidity, basicity, etc.

7. Measurement of Physical Properties
English System Metric System
•The International system of Units (SI) was established in the 11th General Conference
on Weights and Measurement.
NOTE: conversion of units from one system to another is termed dimensional
analysis or factor label method or unit factor method.

8. •Mass and weight: SI unit is kg
Mass: the amount of matter present in a substance.
Weight: the force exerted by gravity on an object.
•Volume: SI unit is m³
For liquids L is used. (1L = 1000mL, 1000cm³ = 1dm³)
Volume: the amount of space that a substance or object occupies, or
that is enclosed within a container.
•Density: SI unit is kg m-3
Density: the amount of mass per unit volume.
•Temperature: SI unit is K
Temperature: the degree or intensity of heat present in a substance or
object
The other units of temperature are °C and °F.
The inter-relations are:
°F = 9/5(°C) + 32
K = °C + 273.15
NOTE: Temperature below 0 °C is possible but in Kelvin scale, negative

9. Uncertainty in Measurement
The problem of doing simple mathematics with very large or very small
numbers is solved by the using scientific notation i.e., exponential notation.
N * 10ⁿ where n is an exponent having positive or negative value.
•Precision: the closeness of various measurement for the same quantity.
•Accuracy: the agreement of a particular value to the true value of the results.
•Significant values: meaningless digits which are known with certainty

10. Rules for determining significant numbers-
• All non-zero digits are always significant.
Eg. 285 has three significant values.
•Any zeros between two significant digits are significant
•Zeroes preceding the first non-zero digit are not significant.
A final zero or trailing zeros in the decimal portion ONLY are significant
Eg. .500 or .632000 the zeros are significant
.006 or .00096 the zeros are NOT significant
•Zeroes at the end or right of a number are significant provided they’re on the
right side of the decimal.
Eg. 100 has one significant figure
100. has three significant figures
100.0 has four significant figures
•Counting numbers of object have infinite significant figures as there are exact
numbers

11. LAWS OF CHEMICAL COMBINATION
•LAW OF CONSERVATION OF MASS
Matter can neither be created nor destroyed.
•LAW OF DEFINITE PROPORTION/COMPSITION
A given compound always contains exactly the same proportion of element by
weight.
•LAW OF MULTIPLE PROPORTION
If two elements combine to form more than one compound , the masses of one
element that combine with a fixed mass of the other element, are in the ratio of
small whole numbers.
•GAY LUSSAC’S LAW OF GASEOUS VOLUMES
When gases combine or are produced in a chemical reaction they do so in a simple
ratio by volume provided all gases are at the same temperature and pressure.
•AVAGADRO’S LAW
Equal volumes of gases at same temperature and pressure should contain equal
number of molecules.

12. 1) Matter consist of indivisible atoms.
2) All atoms of a given element are identical in properties including mass.
3) Compounds are formed when atoms of different element combine in a fixed
ratio.
4) A chemical reaction is a rearrangement of atoms.

13. ATOMIC MASS
•One atomic mass is defined as the mass exactly equal to one-twelfth the mass of
one carbon-12 (¹²C) atom.
•In this system, ¹²C is assigned a mass exactly 12 atomic mass unit (amu) and
amasses of all other atoms are given relative to this standard.
•Atomic mass unit ‘amu’ is replaced by unified mass ‘u’.
MOLECULAR MASS
•Molecular mass is the sum of atomic masses of the elements present in a
molecule.
Molecular mass = (A₁*N ₁) + (A₂*N ₂) +….
A=atomic mass of each element
N=number of its atoms
FORMULA MASS
•Formula mass is the sum of the average atomic masses of all the atoms in the
compound’s formula.

14. MOLE CONCEPT AND MOLAR MASSES
•One mole is the amount of a substance that contains as many particles
or entities as there are atoms in exactly 12g of the ¹²C isotope.
Knowing one mole of carbon weighs 12g,the number of atoms in it
is equal to:
= 12g/mol ¹²C .
1.992648 * 10¯²³ g/ ¹²C atom
= 6.022 * 10²³ atoms/mol
This number is termed Avogadro's constant and denoted by NA.
•The mass of one mole of a substance in grams is called its molar mass.
Molar mass= atomic mass/ molecular mass/ formula mass in u

15. PERCENTAGE COMPOSITION
Mass % of an element = mass of that in the compound * 100
molar mass of the compound
EMPIRICAL FORMULA FOR MOLECULAR FORMULA
An empirical formula is the simplest whole number ratio of various
atoms present in a compound.
Molecular formula is the exact number of different types of atoms
present in the molecule of a compound

16. The word ‘stoichiometry’ is derived from two Greek words — stoicheion (meaning,
element) and metron (meaning, measure).
Stoichiometry deals with the calculation of masses/volumes of the reactants and the
products involved in a chemical reaction.
Let us consider the combustion of methane. A balanced equation for this reaction is as
given below:
CH4 (g) + 2O2 (g) → CO2 (g) + 2 H2O (g)
Here, methane and dioxygen are called reactants and carbon dioxide and water are called
products.
The coefficients 2 for O2 and H2O are called stoichiometric coefficients. Similarly the
coefficient for CH4 and CO2 is one in each case. They represent the number of molecules
(and moles as well) taking part in the reaction or formed in the reaction.

17. Thus, according to the above chemical reaction:
• One mole of CH4(g) reacts with two moles of O2(g) to give one mole of
CO2(g) and two moles of H2O(g)
• One molecule of CH4(g) reacts with 2 molecules of O2(g) to give one
molecule of CO2(g) and 2 molecules of H2O(g)
• 22.7 L of CH4 (g) reacts with 45.4 L of O2 (g) to give 22.7 L of CO2 (g) and 45.4
L of H2O(g)
• 16 g of CH4 (g) reacts with 2×32 g of O2 (g) to give 44 g of CO2 (g) and 2×18 g
of H2O (g).
CH4 (g) + 2O2 (g) → CO2 (g) + 2 H2O (g)
mass ⇌ moles ⇌ no. of molecule
Mass_
Volume
= Density

18. The limiting reagent (or limiting reactant or limiting agent) in a chemical
reaction is a reactant that is totally consumed when the chemical reaction is
completed.
Many a time, reactions are carried out with the amounts of reactants that are
different than the amounts as required by a balanced chemical reaction. In such
situations, one reactant is in more amount than the amount required by balanced
chemical reaction. The reactant which is present in the least amount gets
consumed after sometime and after that further reaction does not take place
whatever be the amount of the other reactant. Hence, the reactant, which gets
consumed first, limits the amount of product formed and is, therefore, called the
limiting reagent.

19. Reactions in Solutions
The concentration of a solution or the amount of substance present in its given
volume can be expressed in any of the following ways.
1. Mass per cent or weight per cent (w/w %)
Mass per cent= mass of solute * 100
mass of solution
2. Mole fraction
If a substance ‘A’ dissolves in substance ‘B’ and their number of moles are nA
and nB, respectively, then the mole fractions of A and B are given as:
Mole fraction of A= No. of moles of A__
No. of moles of solution
= nA .
nA + nB
Mole fraction of B= No. of moles of B___
No. of moles of solution
= nB .
nA+nB

20. 3. Molarity
It is the most widely used unit and is denoted by M. It is defined as the
number of moles of the solute in 1 litre of the solution.
Molarity (M) = No. of moles of solute _
Volume of solution in litres
4. Molality
It is defined as the number of moles of solute present in 1 kg of solvent. It is
denoted by m.
Molality(m) = No. of moles of solute _
Mass of solvent in kg