Atomic theory

Historic approaches to atomic theory

Democritus

J.J. Thompson's plum pudding

John Dalton

Law of octaves

Other stuff

Earnest Rutherford

Niels Bohr

Avogadro's number

If the mass of one molecule of a substance is M a.m.u (atomic mass units) then one gramme molecule (aka a mole) is defined to be Mgm (grammes).

Avogadro's number (commonly written N) is a universal constant which is defined as the number of molecules in one mole of any substance. There are many experiments from which its value can be deduced. $$ N \approx 6 \times 10^{23} $$

1 a.m.u = (\frac{1}{N})gm

In the same way that a gram molecule (mole) is defined, a gram ion can also be defined. The total charge of one gram ion of any substance is defined to be Ne where e is the charge of a single ion of that substance.

Intermolecular forces

There are two types of force between molecule – the attractive and repulsive forces (denoted F_W and F_R respectively). The attractive force is dominant at about 2-3Å and the repulsive force is dominant at about 1-2Å.

Intermolecular forces decrease quickly as distance increases.