Ex

  Chemistry (NTSE/Olympiad)  

3. Atoms & Molecules

Mole Concept

Atoms and molecules are so small in size that they cannot be counted individually. The chemists use the unit mole for counting atoms, molecules or ions. It is represented by n. A mole represents 6.022 × 1023 particles.
Example. 1 mole of atoms = 6.022 × 1023 atoms.
1 mole of molecules = 6.022 × 1023 molecules The number of particles present in 1 mole of any substance is fixed i.e. 6.022 × 1023.
This number is called Avogadro constant or Avogadro number. It is represented by No. 1 mole of atoms = 6.022 × 1023 atoms = Gram atomic mass or Molar mass of element





No. of moles = n
Given mass = m
Molar mass = M
Given number of particles = N
Avogadro number of particles = N0
These relations can be interchanged as
Mass of element, m = n × M
or No. of particles of element, N = n × N0
Similarly,
1 Mole of molecules = 6.022 × 1023 molecules
= Gram molecular mass of Molar mass




or m = n × M and N = n × N0

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