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John Dalton
He stated his theory in a lecture to the Royal Institution in 1803. The theory proposed a number of basic ideas: 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
1- was a British chemist and physicist who attended the Royal College of Chemistry, London, and worked onspectroscopy
2- Crookes was the inventor of the Crookes radiometer,
3- He published numerous papers on spectroscopy and conducted research on a variety of minor subjects. In his investigations of the conduction of electricity in low pressure gases
4- later he became involved in the Theosophical Movement and there are references to his having exorcised demons.
5- In 1897 Crookes was kni -
jj Thomson
-His great discovery occurred in 1897 during the course of his investigations of cathode rays. Thomson provided convincing evidence that the rays consisted of charged particles;
-His discovery of the electron won the Nobel Prize in 1906 and he was knighted two years later. Thomson was described by Rutherford as having "a most radiating smile, … when he is scoring off anyone."
-discovers the electron, using properties of cathode rays. -
Ernest Rutherford
-known as the father of nuclear physics
-British physicist, who became a Nobel laureate for his pioneering work in nuclear physics and for his theory of the structure of the atom. -He used a gold foil experiment, observing the scattering of alpha particles, and demonstrated for the first time the existence of the atomic nucleus. -
quantum mechanical model
The Rutherford planetary model of the atom is often what sticks in students’ minds. It provides a neat and familiar picture of electrons orbiting a central nucleus like planets around the Sun. Because of this, it can be challenging to replace this picture with one that more accurately represents the quantum-mechanical model used by modern physicists: an atom with a tiny nucleus with probability waves instead of sharp orbits to describe the distribution of electrons, which have fuzzy positions bu -
James Chadwick
James predicted the atom would have a neutron.
He established that atomic number is determined by the numbers of protons in an atom.
He also discovered the fourth subatomic particle,the neutron. -
Bohr model 1963
in 1913, depicts the atom as small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity. -
Niels Bohr
-made numerous contributions to our understanding of atomic structure and quantum mechanics.
-He also integrated the Planck quantum theory, stating that when electrons change orbits they emit a quantum of discrete energy.
-Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.
