Atomic Theory (2)

Antoine Lavoisier - Law of Conservation of Matter

John Dalton - 4 Postulates on Matter

• all elements are composed of atoms

• all atoms of a given element are identical and atoms of diff. elements are different

• atoms are not changed into diff. atoms in reactions, only re-arranged. Atoms are not created or destroyed

• compounds are formed when atoms of different elements join together

J.J. Thompson - Cathode Ray Experiment (different gases electrified and a beam of light was always produced, beam could be bent using electric and magnetic field, always away from negative, caused by negative particles)

Robert Millikan - Oil Drop Experiment (oil would drop between two charged plates, by altering the charges on the plates the speed of falling droplets could be changed, able to determine exact mass (5.486×10-4 AMU) and exact charge of a single electron

Ernest Rutherford - Gold Foil Experiment (alpha particles were fired at a thin sheet of gold foil, most particles went straigth through but some were deflected, atoms are mostly empty space but contain very dense positive center, called this the ‘nucleus’)

Neils Bohr - identified electrons orbiting the nucleus at specific distances - energy levels

Modern Theory

• nucleus is composed of protons and neutrons

• electrons orbit the nucleus in various 3-D shapes called “electron clouds”