Revision: Mole Concept and Stoichiometry >> Relative Atomic Mass, Relative Molecular Mass and Mole Concept Chemistry (English Medium) ICSE Class 10 CISCE

The relative atomic mass or atomic weight of an element is the number of times one atom of the element is heavier than A times of the mass of an atom of carbon-12.

Relative Atomic Mass = \[=\frac{\text{Mass of 1 atom of the element}}{\frac{1}{12}th\text{ the mass of one C-12 atom}}\]

The relative molecular mass (or molecular weight) of an element or a compound is the number that represents how many times one molecule of the substance is heavier than 1/12 of the mass of an atom of carbon-12.

The atomic mass of an element expressed in grams is called gram atomic mass.

The quantity of the element which weighs equal to its gram atomic mass is called one gram atom of that element.

The molecular mass of a substance expressed in grams is called gram molecular mass or molar mass.

The quantity of the element which weighs equal to its gram atomic mass is called one gram atom of that element.

Avogadro’s number is defined as the number of atoms present in 12g of ₆C¹² isotope i.e. 6.023 × 10²³ atoms.

"The relative atomic mass or atomic weight of an element is the number of times one atom of the element is heavier than `1/12` times of the mass of an atom of carbon - 12".
Relative atomic mass = Mass of 1 atom of the element `1/12` of the mass of one C¹² atom.

Mole is the amount of a substance containing elementary particles like atoms, molecules or ions in 12 g of carbon - 12.

One mole of any gaseous molecules occupies 22.4 dm³ (litre) or 22400 cm³ (ml) at standard temperature and pressure (STP). This volume is known as the molar volume.

The relative molecular mass of a compound is the number that represents how many times one molecule of the substance is heavier than `1/12` of the mass of an atom of carbon ₆C¹².

A mole is the amount of pure substance containing the same number of chemical units as there are atoms in exactly 12 grams of carbon -12.

Avogadro's number is defined as the number of atoms present in 12 g (gram atomic mass) of C-12 isotope, i.e., 6·022 x 1023 atoms.

OR

Avogadro's number is the number of elementary units, i.e., atoms, ions or molecules present in one mole of a substance. It is denoted by N_A.

"One mole of atoms contains 6·022 × l0²³ atoms having mass equal to its gram atomic mass."

The molar volume of a gas can be defined as the volume occupied by one mole of a gas at S.T.P.

OR

The molar volume of a gas is the volume occupied by one gram molecular mass or simply, by one mole of the gas at S. T.P. It is  equal to 22·4 dm³.

The molar volume of a gas is the volume occupied by one gram molecular mass or simply, by one mole of the gas at S.T.P. It is equal to 22·4 dm³.

Vapour density is defined as the ratio between the masses of equal volumes of gas (or vapour) and hydrogen under the same conditions of temperature and pressure.

The ratio between the masses of equal volumes of gas (or vapour) and hydrogen under the same conditions of temperature and pressure.

One mole of atoms = 6·022 x 10²³ atoms
                               = Gram atomic mass of an element
                               = 1 g atom of the element

One mole of molecules = 6·022 x 10²³ molecules
                                      = Gram molecular mass
                                      = 1 g molecule of the compound. 

Mass of one atom = \[\frac{\text{Atomic Mass}}{6\cdot022\times10^{23}}\]

Mass of one molecule = \[\frac{\text{Molecular Mass}}{6\cdot022\times10^{23}}\]

One mole of a gas = 22·4 litres at S.T.P.

The relative molecular mass of a gas or vapour is twice its vapour density.

2 × Rel. V.D. = Rel. molecular mass of a gas or vapour.