Page 1 - 3. LESSON NOTES-(MOLE CONCEPT)

SAI International School
Class-IX

Subject- Chemistry
Topic-Atoms and Molecules
Topic-Mole concept

Lesson Note
Recaptulation:

Atomic mass or Relative atomic mass:Atomic mass of an element may be
defined as the average relative mass of an atom of the element as compared with

th
1/12 of the mass of an atom of carbon (C-12 isotope) taken as 12 amu.

Molecular mass or relative molecular mass of the substance:
The relative molecular mass of the substance can be defined as the mass of one
th
molecule of the substance compared with 1/12 of the mass of one atom of carbon
which is taken as a standard. It is expressed in terms of amu or u.

Gram Atomic Mass: The gram atomic mass of an element is its relative atomic
mass expressed in grams
e.g. Relative atomic mass of oxygen is 16 u and its Gram atomic mass is 16g
Gram Molecular Mass:The gram molecular mass of a substance is its relative
molecular mass expressed in grams.
E.g. Relative molecular mass of H2O is 18 u and its gram atomic mass is 16 g

A mole is defined as the amount of a substance that contains exactly
6.022 X 10 ‘elementary entities’ of the given substance.
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The number 6.022X10 is popularly known as the Avogadro constant and is often denoted by the
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symbol ‘N A’. The elementary entities that can be represented in moles can be atoms, molecules,
monoatomic/polyatomic ions, and other particles (such as electrons).
For example, one mole of a pure carbon-12 ( C) sample will have a mass of exactly 12 grams
12
and will contain 6.022X10 (N A) number of C atoms. The number of moles of a substance in a
12
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given pure sample can be represented by the following formula:
Mole Concept: A mole is defined as the amount of a substance that
contains exactly 6.02214076X10 ‘elementary entities’ of the given
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substance.
Mole: A collection of 6.022 × 10 particles is named as one mole.
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1 mole = 6.022 × 10 particles = Mass of 1 mole particles in grams
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The mass of 1 mole particles is equal to its mass in grams.

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