Some Basic Concepts in Chemistry: Quick Review

The mole is the SI unit of amount of substance, with 1 mole containing exactly $6.022 \times 10^{23}$ entities — Avogadro's number.
The molar mass of any substance in grams per mole numerically equals its atomic or molecular mass in atomic mass units.
One mole of any ideal gas occupies 22.4 litres at STP (0 °C, 1 atm) — a direct consequence of Avogadro's Law.
The five laws of chemical combination — Conservation of Mass, Definite Proportions, Multiple Proportions, Gay-Lussac's Law, and Avogadro's Law — were established between 1789 and 1811.
Percentage composition of an element equals $\frac{n × atomic mass}{molar mass}$ × 100, and from it the empirical formula is derived by dividing each ratio by the smallest.
The molecular formula is obtained by multiplying the empirical formula by n, where n = molar mass ÷ empirical formula mass.
The limiting reagent is the reactant with the smallest value of $\frac{moles}{stoichiometric coefficient}$ and it determines the theoretical yield.
Molarity (moles per litre) is temperature-dependent because solution volume changes with temperature, while molality (moles per kilogram of solvent) is temperature-independent.
The interconversion from mass% to molarity is M = (1000 × d × w%) / (Mr × 100), and to molality is m = (1000 × w%) / (Mr × (100 − w%)).
Normality equals Molarity multiplied by the n-factor, and the equivalent weight of a substance equals its molar mass divided by its n-factor.