🧪 Some Basic Concepts of Chemistry

1. Matter and its Nature

Matter is anything that has mass and occupies space. It can exist in three physical states: solid, liquid, and gas. Macroscopically, matter is classified into Mixtures (homogeneous and heterogeneous) and Pure Substances (elements and compounds).

2. Laws of Chemical Combination

Law of Conservation of Mass (Lavoisier): Matter can neither be created nor destroyed.
Law of Definite Proportions (Proust): A given compound always contains exactly the same proportion of elements by weight.
Law of Multiple Proportions (Dalton): If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers.

3. Atomic and Molecular Masses

⚖️ Atomic Mass Unit (amu or u)

One atomic mass unit is defined as a mass exactly equal to one-twelfth the mass of one carbon-12 atom.

Molecular Mass: The sum of atomic masses of the elements present in a molecule. Formula Mass is used for ionic compounds.

4. Mole Concept and Molar Mass

1 Mole = 6.022 × 10²³ particles (Avogadro's Number)

The mass of one mole of a substance in grams is called its molar mass.

Empirical and Molecular Formula

Empirical Formula: Represents the simplest whole number ratio of various atoms present in a compound.

Molecular Formula: Shows the exact number of different types of atoms present. (Molecular Formula = n × Empirical Formula).

5. Stoichiometry and Concentration of Solutions

Stoichiometry deals with the calculation of masses (and sometimes volumes) of the reactants and products involved in a chemical reaction.

Concentration Terms

Molarity (M): Number of moles of solute per liter of solution. (Temperature dependent)

Molality (m): Number of moles of solute per kilogram of solvent. (Temperature independent)

Mole Fraction (x): Ratio of moles of one component to total moles.