the history of the atom

describe the first theory of the atom

by Democritus. everything is made up of tiny particles which cannot be broken down further

describe the second theory of the atom

by John Dalton. atoms as solid spheres - different spheres make up different elements

describe the third theory of the atom

plum pudding model by J.J Thompson. atoms couldn’t be solid spheres and must contain negatively charged particles. general ball of positive charge with discreet electrons stuck in it

describe the fourth theory of the atom

nuclear model by Ernest Rutherford who fired positively charged alpha particles through a thin sheet of gold - some were deflected. compact nucleus contains positive charge, negative charge exists as a cloud around.

problems with fourth theory of the atom

nothing stopping electrons attracting inwards

describe the fifth theory of the atom

by Niels Bhor. electrons orbit the nucleus in shells which prevent atom from collapsing

describe today’s theory of the atom

further experiments from Rutherford. positive charge in nucleus is made up of protons. James Chadwick provided evidence for neutrons. protons and neutrons make up a nucleus which electrons orbit in shells