Chemistry is the study of matter and its composition, structure, properties, and interactions. [1] Some key concepts introduced in the document include the classification of matter as elements, compounds, or mixtures based on its chemical and physical properties. [2] Five important laws governing chemical combinations are also outlined: the law of conservation of mass, the law of definite proportions, the law of multiple proportions, Gay-Lussac's law of gaseous volumes, and Avogadro's law. [3]

1. SOME BASIC CONCEPTS OF
CHEMISTRY
CHAPTER 1
CLASS XI

2. WHAT IS CHEMISTRY ?
“Chemistry is the study of
composition, structure, properties and
interaction of matter”
“science is the great antidote to the poison of
enthusiasm and superstition.”
- Adam Smith
(Scottish Philosopher)

3. APPLICATION FIELDS OF CHEMISTRY
• Chemicals used in manufacturing of chips and
components of computers.
• Different chemical composition in atmosphere creates
different climatic conditions.
Eg: acid rain, increased green house gases(GHG) causes
increased heat in atmosphere and related effects.
• In human body different chemicals are present which
help in its functionality and specific purpose.
Eg: NO acts as messenger for brain cells messages and prevents
tumor cells…
• Production of DDTs, disinfectants , and related
chemicals for chemical industries
• Production of cosmetics, soaps, oils, creams, related
health care products.

4. What is matter?
“Anything that can occupy space, can be felt by more than
one of our senses, andposses definite mass can be
definedas matter”
Eg : Air, water, living things, books….

5. CLASSIFICATION OF MATTER
Matter
Based on chemical
properties
Mixtures
Homogenous
mixtures
Heterogeneou
s mixtures
Pure
Substances
Elements Compounds
Based on
physical
properties
Solids Liquids Gases

7. International system of Units
Base Physical
Quantity
Symbol for
Quantity
Name of SI Unit Symbol for SI Unit
Length L Meter m
Mass M Kilogram Kg
Time t second s
Electric Current I Ampere A
Thermodynamic
Temperature
T Kelvin K
Amount of
substance
n Mole mol
Luminous Intensity Iv Candela cd
Table 1 : Basic Physical Quantities and their Units

8. Unit Conversions
Multiple Prefix Symbol
10-9 Nano n
10-6 Micro µ
10-3 Milli m
10-2 Centi c
10-1 Deci d
10 Deca da
103 Kilo k
106 Mega M
Table 2: Some common unit conversions

9. Some Important Notes
❖To indicate very small numbers we use negative
exponents.
❖To indicate large numbers we use positive exponents.
❖Scientific notation is the proper representation of a
number in exponential form.
❖Precision indicates how closely repeated measurements
match each other.
❖Accuracy indicates how closely a measurement matches
the correct or expected values.
❖A result is valid only if it is both accurate and precise.

10. Rules for determining the number of significant
figures.
1. All non zero digits are significant.
2. Zeroes preceding to first non zero digits are not
significant. Such zero indicates the position of decimal
point.
3. Zeroes between two non zero digits are significant.
4. Zeros at the end or right of a number are significant
provided they are on the right side of the decimal point.
5. During addition and subtraction the result cannot have
more digits to the right of the decimal point than either of
the original numbers.
6. In multiplication and division with significant figures, the
answer cannot have more significant figures than either of
the original numbers.

11. LAWS OF CHEMICAL COMBINATIONS
• There are 5 basic laws of chemical
combinations that govern every reaction:
❑ Law of conservation of mass
❑ Law of definite proportion
❑ Law of multiple proportions
❑ Gay Lussac’s law of gaseous volumes
❑ Avogadro law

12. LAWS OF CHEMICAL COMBINATIONS
➢ Law of conservation of mass:
“It sates that matter can neither be created nor destroyed, it
can be converted from one form to other.”
➢ Law of definite proportions :
“Irrespective of the source, a given compound always
contains same elements in the same proportion .”
➢ Law of multiple proportions :
“If two elements can 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.”

13. LAWS OF CHEMICAL COMBINATIONS
➢ Gay Lussac’s law of gaseous volumes :
“When gases combine or are produced in a chemical
reactions they do so in a simple ratio by volume
provided all gases are at same temperature and
pressure.”
➢ Avogadro law :
“At the same temperature and pressure equal volumes of
gases contain equal number of molecules.”

14. Daltons Atomic Theory
In 1808 Dalton published , ‘A New System of
chemical philosophy’ in which he proposed the
following:
• Matter consists of indivisible atoms.
• All the atoms of a given element have identical
properties including identical mass. Atoms of
different elements differ in mass.
• Compounds are formed when atoms of different
elements combine in a fixed ratio.
• Chemical reactions involve reorganization of
atoms. These are neither created nor destroyed
in a chemical reaction.

15. Important Terms
• 6.022 x 1023 is called Avogadro’s constant or
Avogadro’s number.
• A mole is a collection of 6.022 x 1023 particles.
• One mole is the amount of a substance that
contains as many particles or entities as there are
atoms in exactly 12 g (or 0.012 kg) of the C-12
isotope.
• The mass of one mole of a substance in grams is
called its molar mass.
• The molar mass in grams is numerically equal to
the atomic/molecular/formula mass in u.(u is the
unified mass).

16. • Molarity is the number of moles of solute in per liter of
solution. Unit is moles per liter.
• Molality is the number of solute present in 1kg of
solvent.
• Atomic Mass: Average relative mass of an atom of an
element as compared with the mass of a carbon atom
taken as 12 amu.
• Atomic mass expressed in grams is called gram atomic
mass.
• Molecular Mass : Sum of the atomic masses of
elements present in a molecule.
• Molecular mass expressed in grams is called gram
molecular mass.
• Formula Mass: Sum of atomic masses of all atoms in a
formula unit of the compound.
• An empirical formula represents the simplest whole
number ratio of various atoms present in a compound.

17. • Molecular formula shows the exact number of
different types of atoms present in a molecule
of a compound.
• If the mass per cent of various elements
present in a compound is known, its empirical
formula can be determined. where n is a
simple number and may have values 1, 2, 3….
Molecular formula = n(Empirical formula)

18. Important Formulae to remember