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Democritus
His theory consisted of the following:
-All matter consists of invisible particles called atoms
-Atoms are indestructible
-Atoms are solid but invisible
-Atoms are homogenous
-Atoms differ in size, shape, mass, position, ans arrangement
He also believed that solids were made up of small, pointy atoms, liquids were made up of large, round atoms, and oils were made up of very fine, small atoms that could easily slip past each other. Democritus's model was just a solid sphere. -
John Dalton
His theory included:
-All matter is made of atoms
-Atoms are indivisible and indestructible
-All atoms of a given element are identical in mass and properties
-Compounds are formed by a combination of two or more different kinds of atoms
-A chemical reaction is a rearrangement of atoms
Dalton assumed that water contains one atom of hydrogen and one atom of oxygen and concluded that the relative weight of the oxygen atom must be 5.6 times as large as the hydrogen atom. -
J.J. Thomson
He believed atoms are made up of small particles and are divisble. He discovered the electron. Cathode tube experiment.
Properties of an electron:
-Electrons travel in a straight line
-Electrons have momentum and kinetic energy
-Electrons produce heat when they strike
-X-rays are emitted by the electrons
-When electron field and magnetic field are applied, the electrons defect
-Electrons travel with high velocities
-Electrons produce fluorescence when they strike crystals, minerals and salts -
Ernest Rutherford
His theory includes:
-The atom's electron cloud does not influence alpha particle scattering
-Most of an atom's positive charge is concentrated in the center; this concentrated central mass and charge is responsible for deflecting both alpha and beta particles
-The atom itself is about 100,000 times the diameter of the concentrated central mass -
Niels Bohr
Bohr used different equations to prove his theory.
His theory included:
-The electron in a hydrogen atom travels around the nucleus in a circular orbit
-The further the electron is from the nucleus, the more energy it has
-Orbits are quantized
- Light is absorbed when an electron jumps to a higher energy orbit and emitted when an electron falls into a lower energy orbit
-The energy of the light emitted or absorbed is exactly equal to the difference between the energies of the orbits -
James Chadwick
By using his experiment he was able to prove that the radiation causing the ejected particles was much more energetic than could be accounted for by protons. He found that an atom was now a nucleus containing positively charged protons and neutral neutrons. He won the Nobel Prize for discovering the neutron. -
Robert Miliken
He measured the charge on an electron with his experiment (oil-drop appratus). He studied the droplets in his experiement carefully and came to the conclusion that the mass of an electron is at least 1000 times smaller than the lightest atom.
