Atomic Model Timeline :Gullett

Democritus

Oct 27, 1000

Believed that all matter consisted of extremely small particles that can't be divided.

Aristotle

Oct 27, 1000

Didn't think there was a limit to the number of times matter could be divided. He was a philosopher so he just thought about his therory.

Joseph Proust

Oct 31, 1700

Proust’s law is that chemical substances only truly combine to form a small number of compounds, each of which is characterized by components that combine in fixed proportions by weight. His beliefs were were not at first accepted but later on were.

Antoine Lavoisier

Oct 31, 1769

He wrote the first extensive list of elements, and helped to reform chemical nomenclature. He discovered that, although matter may change its form or shape, its mass always remains the same.

Jonh Dalton

Oct 10, 1802

Said all matter is made up of all individual particles called atoms which cannot be divided. He created wooden spheres to represent the atoms of different elements.

J.J. Thomas

Oct 27, 1897

Negative charges scattered positive charged matter said have negative charges because they were attracted to positive.

Hantaro Nagaoka

Oct 28, 1904

Suggested that an atom has a nucleus.Nagaoka developed an early, incorrect "planetary model" of the atom. The model was based around an analogy to the explanation of the stability of the Saturn rings.

Robert millikan

Oct 31, 1909

determined the unit charge of the electron with his oil drop experiment at the University of Chicago. Thus allowing for the calculation of the mass of the electron and the positively charged atoms.

Ernest Marsden

Oct 31, 1909

This theory held that the negatively charged electrons in an atom were floating (sometimes moving) in a sea of positive charge.In detail, a beam of alpha particles, generated by the radioactive decay of radium, was directed normally onto a sheet of very thin gold foil.

Ernest Rutherford

Oct 27, 1911

Discovered uranium emits fast-moving paticles that have a positive charge.

Niel Bohr

Oct 28, 1923

An atom can move from one energy level to another when the atom gains or loses energy focused on the electrons.

Louis de Broglie

Oct 28, 1926

Moving products like electrons having some properties of waves.

James Chadwick

Oct 28, 1932

Confirms the existence of neutrons which have no change.. In contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms.