📘 Chapter 3: Atoms and Molecules

Law of conservation of mass

Mass is neither created nor destroyed

Law of constant proportions

Elements in compound always combine in fixed mass ratio

Dalton's atomic theory

Matter made of indivisible atoms; atoms of same element are identical

Atom

Smallest unit of matter

Molecule

Two or more atoms chemically bonded

Atomicity

Number of atoms in a molecule

Symbol of element

One/two letters representing an element

Valency

Combining capacity of an atom

Ion

Charged particle (cation or anion)

Cation

Positively charged ion

Anion

Negatively charged ion

Atomic mass

Mass of one atom in atomic mass unit (u)

Molecular mass

Sum of atomic masses of all atoms in a molecule

Formula unit mass

Mass of one unit of ionic compound

Chemical formula

Representation of molecule using element symbols

Avogadro's number

6.022 × 10^23 particles in one mole

Mole

Amount of substance containing Avogadro's number of particles

Molar mass

Mass of 1 mole of a substance

Relative atomic mass

Mass of atom compared to 1/12 of C-12 atom

Calculation using mole

Used to count atoms, ions, molecules