Mole Concept | Some Basic Concepts of Chemistry | Class 11     

One gram atom of any element contains the same number of atoms and one gram molecule of any substance contains the same number of molecules.

The value was found to be 6.022137 × 10²³

The value generally used is 6.022 × 10^{23 .}

This is called Avogadro’s number or Avogadro’s constant (N_A)

Avogadro’s number may be defined as the number of atoms present in one gram atom of the element or the number of molecules present in one gram molecule of the substance.

A mole is a chemist unit of counting particles such as atom, molecules, ions, electrons, protons which represent a value of 6.022 × 10²³ 

A mole of hydrogen atom means 6.022 × 10²³  atoms of hydrogen whereas a mole of hydrogen molecule means 6.022 × 10²³  molecules of hydrogen or 2 × 6.022 × 10²³ atoms of hydrogen .

A mole of oxygen molecule means 6.022 × 10²³  molecules of oxygen or 2 × 6.022 × 10²³ atoms of oxygen.

A mole is defined as that amount of substance which has mass equal to gram atomic mass if the substance is atomic or gram molecular mass if the substance is molecular.

1 mole of carbon atoms =12 grams

1 mole of sodium atoms = 23 grams

1 mole of Oxygen atom = 16 grams

1 mole of Oxygen molecule = 32 grams

1 mole of water molecule = 18 grams

1 mole of carbon dioxide molecule = 44 grams

A mole is defined as that amount of substance which contains Avogadro’s number of atoms if the substance is atomic or Avogadro’s number of molecules if the substance is molecular.

1 mole of carbon atoms = 6.022 ×10²³ atoms of carbon.

1 mole of sodium atom = 6.022 ×10²³ atoms of sodium

1 mole of Oxygen atom =6.022 ×10²³ atoms of oxygen

1 mole of Oxygen molecule =6.022 ×10²³  molecules of oxygen

1 mole of water =6.022 ×10²³  molecules of water

In case of gases, a mole is defined as that amount of the gas which has a volume of 22.4 litres at STP.

1 mole of Oxygen gas = 22.4 litres of oxygen at STP

one mole of carbon dioxide gas = 22.4 litres of carbon dioxide at STP

A mole of an ionic compound is defined as that amount of the substance which has mass equal to gram formula mass or which contains Avogadro’s number of formula unit.

1 mole of NaCl = 58.5 grams of NaCl

1 mole of NaCl =6.022 ×10²³ formula units of NaCl = 6.022 ×10²³ Na⁺ ion and 6.022 ×10²³   Cl^– ion.

Importance of Avogadro’s number and mole concept

1. In the calculation of actual mass of a single atom of an element or a single molecule of a substance.
2. In the calculation of the number of atoms or molecules in a given mass of the element of the compound.
3. In the calculation of the number of molecules present in a given volume of the gas under given conditions.
4. In the calculation of the size of the individual atoms and molecules assuming them to the spherical.
5. In the calculation of actual masses of 1 amu or 1 u.

1 amu = 1.6606 × 10^-24 g

1 amu = 1.6606 × 10^-27 kg