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John Dalton
England - formed the atomic theory, which states that all matter is composed of tiny, indestructible particles called atoms that are all alike and have the same atomic weight. -
Daltons Model
All matter is composed of atoms
Atoms cannot be made or destroyed
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are rearranged
Compounds are formed from atoms of the constituent elements. -
William Crooke
England - created the Crookes’ tube and demonstrated that cathode rays travel in straight lines and produce phosphorescence and heat when they strike certain materials. -
J.J Thomson
England - discovered the electron and developed the plum-pudding model of the atom. -
plum pudding atomic model
was proposed in 1904 before the discovery of the atomic nucleus in order to add the electron to the atomic model. In this model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plums" surrounded by positively charged "pudding". -
rutherford model
In 1909 Ernest Rutherford conducted what is now a famous experiment where he bombarded gold foil with alpha particles (Helium nuclei). A source which undergoes alpha decay is placed in a lead box with a small hole in it. Any of the alpha particles which hit the inside of the box are simply stopped by the box. Only those which pass through the opening are allowed to escape, and they follow a straight line to the gold foil. -
Ernest Rutherford
England - used the results of his gold-foil experiment to state that all the mass of an atom were in a small positively-charged ball at the center of the atom. -
bohr model
In the Bohr Model the neutrons and protons (symbolized by red and blue balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun (but the orbits are not confined to a plane as is approximately true in the Solar System). -
quantum mechanical model
The quantum mechanical model was constructed by Erwin Schrödinger.
Electrons are defined as standing waves. The electron probability distribution gives the areas in which the probability of electron presence is high. The exact position of the electron is never known as stated by the Heisenberg uncertainty principle: -
Neils Bohr
Denmark - stated that the electrons moved around the nucleus in successively large orbits. He also presented the Bohr atomic model which stated that atoms absorb or emit radiation only when the electrons abruptly jump between allowed, or stationary, states. -
James Chadwick
discovered the neutrally-charged neutron.
