Module 2.1: Atoms and reactions

ATOMIC MODELS OVER TIME -

• Dalton's atomic theory: Atoms are indivisible. All atoms of one element are the same, and different from atoms of another element.
• Thomson's plum-pudding model: Discovers electrons (negative charge, tiny mass). Disproved Dalton's theory - atoms can be split further. Model: Electrons in a 'sea' of positive charge. Atom overall is neutral.
• Rutherford's nuclear model: Alpha scattering experiment showed that atoms are mostly empty space, with their mass concentrated in their positive nucleus (at the centre of the atom). Electrons orbit the nucleus.
• Bohr's planetary model: Electrons orbit the nucleus in shells.
• Discovery of protons (Rutherford) and neutrons (Chadwick) in the nucleus.

ATOMIC MASSES -

• Relative atomic mass: Weighed mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.
• Relative isotopic mass: Mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12. 

AMOUNT OF SUBSTANCE -

• Avogadro constant: Number of atoms per mole (12g) of carbon-12.
• Molar mass: Grams per mole of a substance.

TYPES OF FORMULAE -

• Empirical formula: Simplest whole-number ratio of atoms of each element in a compound.
• Molecular formula: Number of atoms of each element in a molecule.
• Water of…