Some important points in Chemistry

One atomic mass unit(u)	1∕6.02 ✕ 10²³ = 1.66 ✕ 10⁻²⁴g
M₁ = W₁ / 1.66 ✕ 10⁻²⁴	M₁ = atomic mass / molecular mass W₁ = mass of an atom / molecule in gram
Mole	Amount of an any substance containing 6.02 ✕ 10²³ particles.
n₁ = W₁ / M₁	n₁  = Number of moles W₁ = mass in grams M₁ = molecular mass
n₁ = V / 22.4	V = volume in dm³ at STP
n₁ = Number of atoms (or) molecules / NA	NA = 6.02 ✕ 10²³
Empirical formula	Simplest ratio of relative number of atoms of different element in the compound.
Molecular formula	Exact number of atoms in a molecules of the compound.
Excess reactant	Reactant taken in excess amount than required by stoichiometry.