Mole Concept

 

We know atoms make up matter and atoms are the basic building block, it's important to sometimes know how many atoms make a matter. Thus we need some measurement units for calculations and counting of atoms, molecules, ions. Ostwald introduced the term mole.

Mole: One mole is defined as the amount of substance of a system which contains as many entities like, atoms, molecules and ions as there are atoms in 12 grams of carbon.
Later it was found that one gram atom of any substance contains as many atoms as are present in 1 gram atom of a carbon12 isotope.
The value of this number is found to be 6.023X1023 and this is called as Avogadro's number.

Avogadro number:  The number of the particles present in one mole of any substance is equal to 6.022x1023. This is called Avogadro’s number or Avogadro’s constant. 
It is represented by N.

Number of particles in 1 mole
1 mole of hydrogen atoms represents 6.022 × 1023 hydrogen atoms.
1 mole of hydrogen molecules represents 6.022 × 1023 hydrogen molecules.
1 mole of water molecules represents 6.022 × 1023 water molecules.

Examples

a) Find the mass of 1 atom of nitrogen

Solution

Nitrogen has an average atomic weight of 14.0067.

1 mole of nitrogen =14g

1 mole of nitrogen =  6.023x1023 atoms
Mass of  6.023x1023 atoms = 14g
Mass of 1 atom of nitrogen = 14 /6.023x1023 
= 2.32 x10 -23 g.