UNIT I: Some Basic Concepts of Chemistry
Unit II: Structure of Atom
Unit III: Classification of Elements and Periodicity in Properties
Unit IV: Chemical Bonding and Molecular Structure
Unit V: States of Matter: Gases and Liquids
Unit VI: Chemical Thermodynamics
Unit VII: Equilibrium
Unit VIII: Redox Reaction
Unit IX: Hydrogen
Unit X: s -Block Elements (Alkali and Alkaline Earth Metals)

Atoms and Molecules

The smallest particle of an element which may or may not have independent existence is called an atom.

The smallest particle of a substance that is capable of independent existence is called a Molecule.

Atomic Mass Unit

One Atomic Mass unit is defined as a mass exactly equal to one-twelfth the mass of one Carbon-12 atom.

1 \operatorname{amu}=1.66056 \times 10^{-24} \operatorname {g.}

Today ‘ \operatorname{amu}‘ has been replaced by ‘\operatorname {u} ‘, which is known as unified mass.


Atomic Mass

Atomic Mass of an element is defined as the average relative mass of an atom of an element or compound to a mass of an atom of Carbon-12 taken as  12 .

Gram Atomic Mass

The quantity of an element whose mass in grams is numerically equal to its atomic mass.

e.g. Atomic Mass of oxygen = 16 \operatorname { amu }

Therefore Gram Atomic Mass of Oxygen = 16 \operatorname { g.}

Molecular Mass

The molecular mass of a substance is defined as the average relative mass of its molecule as compared to the mass of an atom C-12 takes as  12.

e.g.  CO_2 is  44 times heavier than \dfrac{1}{12} \text {th} mass of an atom of carbon. Therefore molecular mass of  CO_2 is  44 \operatorname { amu }

Gram Molecular Mass

A quantity or substance whose mass in grams is numerically equal to its Molecular Mass called Gram Molecular Mass.

e.g. Molecular mass of Oxygen  =32 \operatorname {amu}.

Thus Gram Molecular Mass of Oxygen =32 \operatorname {g.}

Formula Mass

It is the mass of an ionic compound. It is also equal to the sum of atomic masses of all the elements present in the molecule.

Mole Concept

It is found that one gram atom of any element contains the same number of atoms and one gram of molecule or any substance contains the same number of molecules. This number has been experimentally determined and found to be equal to 6.022137 \times 10^{23} .

The value is generally called Avogadro’s number or  Avogadro’s Constant. It is usually represent as N_A .

 N_A =6.023 \times 10 ^{23}

The mass of one mole of a substance in grams is called its Molar Mass.

Molar Volume

The volume occupied by one mole of any substance is called it’s Molar Volume. It is denoted as V_m.

One mole of all gaseous substances at  273 \operatorname {K} and 1 \operatorname {atm} pressure occupies a volume equal to  22.4 \operatorname{ L} or   22,400 \operatorname {mL} .

The unit of Molar Volume is \operatorname {ltr} \operatorname {mol} ^{-1} or \operatorname {mL} \operatorname {mol} ^{-1} .

Percentage Composition

Mass % of an element in a compound is given by

=\dfrac{\text {mass of that element in the compound}}{\text {molecular mass of compound}}

Percentage Yield

It is the ratio of actual yield of the reaction to the theoretical yield multiplied by  100 .

\% \text { yield }=\dfrac{\text {Actual yield}}{\text {Theoretical yield}}\times 100

Empirical Formula & Molecular Formula

\to An empirical formula represents the simplest whole number ratio of various atoms present in the compound.

e.g.  \operatorname {CH} is the empirical formula of Benzene.

 \to The Molecular formula shows the exact number of different types of atoms present in a molecule of compound.

e.g.  C_6H_6 is the Molecular formula of Benzene.


\text { Molecular Formula } = n \times \text {empirical formula}

\text { Molecular Weight } = n \times \text {empirical weight}

 \text { Also Molecular Weight } = 2\times \text {vapor density}



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