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John Dalton
1.) All matter is made of atoms. Atoms are indivisible and indestructible.
2.) All atoms of a given element are identical in mass and properties.
3.) Compounds are formed by a combination of two or more different kinds of atoms.
4.) A chemical reaction is a rearrangement of atoms. -
J.J. Thomson
Thomson made cathode rays by firing electrical currents through glass popes filled with low-density gas. He measured the ratio of the mass of the cathode ray to its electrical charge. He found out the results of this experiment indicated that the current inside the cathode ray tube was made of tiny particles that carried a negative charge. He named them electrons. -
Hantaro Nagaoka
He developed the earliest published quasi-planetary model of the atom. He assumed that the atom is a large, massive, positively charged sphere, encircled by very many light-weight, negatively charged electrons, bound by electrostatic forces analogous to Saturn's ring. In 1908 he abandoned the Saturnian model because J J. Thomson mentioned that he's planetary model lacked of stability. -
Ernest Rutherford
Rutherford dedused that the postive charge in an atom is the concentrated into a small compact nucleus. They bombarded the foils with high energy alpha particles and observed the number of scatter alpha particles as a function of angle. Thomson's model of the atom said that all alpha particles should have been found within a small fraction of a degree from the beam. -
Neils Bohr
The Bohr Model is like the "planetary model" but there are ways it is different. The basic form of quantum mechanics that is incorporated in the Bohr Model and is completely different from the analogous planetary model. The lowest energy state of a Hydrogen atom is called the ground state. The states with way more energy than the ground state are called the first excited state, the second excited state. and so on. -
Werner Heisenberg & Erwin Schrodinger
The model they helped develop provides the means of visualizing the position of electrons in an atom. In the Bohr model, electrons were assigned to different shells. They explained the repeating patterns of chemical properties in the periodic table. Chemists can use the electron cloud model to assign electrons to different atomic orbitals. -
James Chadwick
He joined forces with Ernest Rutherford after WW I and he was intriged by Rutherford's speculation about a subatomic particle with non charge. Then Walter Bothe and Herbert Becker described an unusual type of gamma ray. He reconized that the properties of the radiation were more consistent with what would be expected from Rutherford's nuetral particle. He earned the 1935 Nobel Prize in Physics for proving the existance of the nuetron.
