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Dalton
English chemist who proposed the Atomic Theory which
stated that all matter was composed of small indivisible
particles called atoms. These atoms possess unique
characteristics and weight for different elembets.
He also stated that three types of atoms exist: simple
(elements), compound (simple molecules), and complex
(complex molecules). Atoms are the building blocks of matter according to Dalto. -
Joseph John Thomson
First to measure the electron. Developed the
plum-pudding model of the atom. Describes the atom as a
slightly positive sphere with small negitively charged electrons inside. Performed the Cathode Ray expeiriment, whcih was a tube full of gas with electrodes, and formed a beam of electrons which repelled other negitively charged particles and attracted positive ones. -
Rutherford
Inferred a small, dense, positively-charged nucleus as the
result of the alpha particle scattering gold foil experiment.
Shot alpha particles at gold foil, most went through the foil but some deflected off and others completely bounced back. Led to the conclusion of a dense, positively charged nucleus. Created the Planetary model and said that atoms were mostly empty space. -
Bohr
Stated that electrons could only orbit the nucleus in succesively larger orbits around the nucleus. The outer orbits could hold more electrons. The electrons in the outermost shell determine the properties of the atom. -
Chadwick
Discovered the neutron.
Wondered if something else besides the proton was adding to the mass.
Decided neutrons have no charge.
Neutrons are in the nucleus.
Divided the nucleus into Electrons, Protons, and Neutrons. -
Modern Model
Our current model of the atom says that electrons do not travel in definite paths around the nucleus.
The exact path or position of moving electron cannot be predicted or determined. Rather, there are regions inside the atom were electrons are likely to be found.
Electron clouds – Regions inside an atom where electrons are likely to be found.
