NCERT Class XI: Basic Concepts of Chemistry

Relative Atomic Weight Formula

Actual Mass of one atom of one element/ 1/12th mass of one atom of Carbon-12

1 atomic mass unit

1.66 × 10^-24 grams

Molecular Weight

Actual mass of one molecule/ 1/12th mass of one atom of Carbon-12

Atomicity

total number of atoms in one molecule of elementary substance

Mole

the amount of a substance that contains as many entities (atoms, molecules or other particles) as there are atoms in exactly 0.012 kg (or 12g) of the Carbon-12 isotope.

Avogadro’s Number

6.022 × 10²³ entities

Gram Atomic Mass

When numerical value of atomic mass of an element is expressed in grams

Gram Atomic Molecular

When numerical value of molecular mass of the substance is expressed in grams

Formula for Mole of atoms

Weight(g) / Gram atomic weight

Formula for mole of molecules

Weight(g) / Gram molecular weight

Formula for mole atoms

Atomicity x Mole Molecules

Formula for mole of gas

V/22.4

Formula for mole particles

n = number of particles / N_A

Vapour Density

the ratio of density of gas and that of hydrogen at the same temperature and pressure.

Formula for vapour density

density of gas/density of hydrogen