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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. Thompson
Thomson proved that the atom was divisible. It was discovered by J.J. Thomson that electrons are present in an atom and that they are negatively charged -
Rutherford
Since most of the alpha particles passed straight through the gold foil without any deflection, most of the space within the atoms is empty. Since some of the alpha particles (which are big in size) were deflected by large angles or bounced backwards, they must have approached some positively charged region responsible for the deflection. This positively charged region is now called the nucleus. As very few alpha particles undergone the deflection, it was concluded that the volume oc -
Bohr
Energy of an electron is constant in one of its allowed orbits. As long as an electron remains in its orbit, it neither absorbs nor radiates energy. -
Modern model ( Heisenberg)
Werner Heisenberg elucidated the Uncertainty Principle (1923) Classical physics had always assumed that precise location and velocity of objects was always possible. Heisenberg, however discovered that this was not necessarily the case at the atomic level. In particular, he stated that the act of observation interfered with the location and velocity of small particles such as electrons. -
Chadwick
In 1932, James Chadwick discovered the neutron. Neutrons help stabilize the protons in the atom's nucleus. Because the nucleus is so tightly packed together, the positively charged protons would tend to repel each other normally. Neutrons help to reduce the repulsion between protons and stabilize the atom's nucleus. Neutrons always reside in the nucleus of atoms and they are about the same size as protons.
