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SOME BASIC CONCEPTS OF CHEMISTRY
Introduction:
Chemistry is the science of molecules and their transformations which deals with the
study of matter, its composition, the changes that matter undergoes and the relation
between changes in composition and changes in energy
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Branches of Chemistry:
 Organic Chemistry- This branch deals with study of carbon compounds especially
hydrocarbons and their derivatives
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It largely concerns itself with the study of minerals found
in the Earth's crust
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It is basically concerned
with laws and theories of the different branches of chemistry
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Analytical Chemistry-This branch deals with the qualitative and
quantitative analysis of various substances
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 Nuclear Chemistry- Nuclear reactions, such as nuclear fission, nuclear fusion,
transmutation processes etc
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Importance of Chemistry:
Chemistry plays a central role in science and is often intertwined with other branches of
science
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, including new material
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It also plays an important role in meeting human needs for
food, healthcare products and other material aimed at improving the quality of life
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For example, book, pen, pencil, water, air, all living beings, etc
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It is made up of only one type of atoms, ex
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Compound
Compound is the substance which is made up of two or more elements combined
together in a fixed ratio by their weight e
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, carbon dioxide
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e
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, Sugar + Water, Sodium Chloride + Water, Sand + Water
On the basis of composition, mixtures are of following type:
➢​ Homogeneous mixture: The mixture which has uniform composition through out e
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,
sugar solution
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e
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sand in water
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Atom word means not to be cut
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International System of Units (S
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)
The international system of units (in French Le Systeme International d' Unités abbreviated as SI) was established in 1960 by the 11th general conference on weights
and measures
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Prefixes in SI system
Definition of SI Base Units
●​ Metre: The metre is the length of the path travelled by light in vacuum during a time
interval of 1/(299792458) of a second
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●​ Second: The second is the duration of 9192631770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the ground
state of the caesium-133 atom
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●​ Kelvin: The kelvin, unit of thermodynamic temperature, is the fraction 1/273
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●​ Mole: The mole is the amount of substance of a system which contains as many
elementary entities as there are atoms in 0
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●​ Candela: The candela is the luminous intensity, in a given direction, of a source
that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a
radiant intensity in that direction of 1/683 watt per steradian
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Scientific
notations, significant figures and dimensional analysis help us in many ways in
presenting of data and theoretical calculations
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Thus, 232
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32508 × 102 in scientific notation
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However, accuracy is the agreement of a particular value to the true value of the result
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9 and its measurements taken by two boys are 3
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8
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8 is more accurate as it is closer to the true value
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85 is
more precise than 3
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Significant Figures
i
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There are certain rules for determining the number of
significant figures
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All digits are significant except zero in the beginning of a number
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iii
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For example, 0
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iv
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For example, 0
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v
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Thus, 2
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vi
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e
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000000 or 20 =
20
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Notes: In additions or subtractions, the final result should be reported to the same
number of decimal places as that of the term with the least number of decimal places
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These laws are known as
of chemical combination
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Law of conservation of mass: This law was put forth by Antoine Lavoisier in 1789
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ii
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This law states that a chemical compound is always found to be made of
same elements combined together in fixed proportion by weight
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iii
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According to
this law, When two elements combine to form two or more chemical compounds,
then weight of one of the element which combines with a fixed weight of the other,
bears a simple whole number ratio to one another
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For example, The ratio of masses of oxygen in CO and CO2 for fixed mass of

carbon (12) is 16 : 32 = 1 : 2
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Law of reciprocal proportions: It states that the ratio of weights of two elements A and
B, which combine separately with the fixed weight of a third element C is either
same or some simple whole number of the ratio of weights in which A and B
c

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