The Discovery of Atomic Structure: The Scientists

Democritus

Greek philosopher, about 400 BC: Proposed that all matter is made up of tiny, invisible particles called atoms.

Robert Boyle

Regarded as the first modern chemist, defined the element as a substance that cannot be broken down into two or more simpler substances by chemical means.

Joseph Priestley

English educator. Discovered oxygen in 1794.

Antoine Lavoisier

French chemist, proposed the Law of Conservation of Mass. Father of modern chemistry.

Joseph Proust

French Chemist. 1799 Proposed Law of Definite Proportions: a given compound always contains the same elements in the same proportions by mass.

John Dalton

English schoolteacher. In 1803, he proposed the Atomic Theory of Matter

Benjamin Franklin

American philosopher. Flew a kite attached to a key in a thunderstorm to study electricity. Concluded there are two kinds of electrical charges, which he called positive (+) and negative (-).

Michael Faraday

English chemist. 1839 Suggested that the structure of atoms is related to electricity.

J.J. Thomson

English physicist. Concluded that the cathode ray was composed of negatively charged particles (electrons), proposed the plum-pudding model of the atom

Robert Millikan

American physicist. Oil drop experiment, determined the charge of a single electron, determined the mass of the electron

Henri Becquerel

French physicist, discovered radioactivity in 1896.

Ernest Rutherford

New Zealand chemist. Gold Foil Experiment, concluded that the atom is mostly empty space with a tiny, positively charged, dense nucleus. He proposed that the negatively charged electrons orbited the nucleus.

Niels Bohr

Danish physicist, solved hydrogen-atom spectrum in 1913. Proposed model of hydrogen atom that linked the atom's electron with photon emission. According to the model, electrons travel around nucleus in fixed orbits.

Henry Moseley

British chemist and physicist. Named individual positive charged proton. Established that the atomic number of the atom defines the identity of the element (equals the number of protons).

James Chadwick

British physicist, discovered neutrons in 1932

Max Planck

German physicist, proposed that hot objects don't emit electromagnetic energy continuously, suggested that objects emit energy in small, specific amounts called quanta (E=hv)

Albert Einstein

German physicist who proposed that electromagnetic radiation has a dual wave-particle nature. He called the particles of light photons.

Louis de Brogile

French scientist who suggested that electrons be considered waves confined to the space around an atomic nucleus.

Werner Heisenberg

A German physicist that speculated that there was no real certainty in where an electron was, and only tendencies.

Erwin Schrodinger

Austrian physicist, developed equation that treated electrons as waves, proposed that electrons exist around the nucleus in orbitals

quantum theory

describes mathematically the wave properties of electrons