1. Laws of Chemical Combination
- Law of Conservation of Mass: Mass can neither be created nor destroyed
in a chemical reaction.
- Law of Constant Proportions: In a chemical substance, the elements are
always present in definite proportions by mass.
2. Dalton's Atomic Theory
All matter is made of very tiny particles called atoms, which are indivisible and cannot be
created or destroyed in a chemical reaction. Atoms of a given element are identical in mass
and chemical properties.
3. Atoms and Molecules
- Atom: The smallest unit of an element that maintains the properties of
that element.
- Molecule: A group of two or more atoms that are chemically bonded
together.
- Atomicity: The number of atoms constituting a molecule (e.g., O₂ is
diatomic, Ar is monoatomic).
4. Mole Concept
A mole is the amount of substance that contains as many particles as there are atoms in
exactly 12g of Carbon-12. This number is 6.022 × 10²³ (Avogadro Constant).
Molar Mass: The mass of 1 mole of a substance in grams.