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Democritus
Democritus
Democritus was a Greek philosopher. He was credited with naming particles atoms. Atoms come from the word "atomos" which means cant be divided. Democritus believed that atoms are an infinite number, always moving, could combine with other atoms, and each substance had atoms of unique shape and size -
John Dalton
Dalton's Atomic Theory
Dalton's model explained that atoms were tiny invisibly, indestructible and indivisible particles: each had a certain mass, size, chemical behavior that determined by what kind of element they were. He called his model the "Billiard Ball model" because he thought that atoms looked like billiard balls from pool. -
J.J. Thomsom
J.J Thomas Thomson was the first scientist to discover tatoms consisted of smaller particles. Thomson won the 1906 Nobel Prize in physics, and found that there was a positive and negative portion of atoms. Thomson called negative particles electrons. Thomson experimented with a device known as a cathode Ray tube. He proposed a model similar to a chocolate chip cookie. the electrons where the chocolate and + made the rest. -
Ernest Rutherford
rutherfordRutherford was a former student of Thomson, he won the Nobel Prize in chemistry in 1908. Rutherford found that Thomson's atomic model was incorrect. He used thin gold foil and alpha particles to determine two things- a) the positive charge was located in the center or the nucleus of the atom.and b) most of the atom was empty space. Rutherfords model is oftenreferred to as a planitary model. -
Francis Aston
francis Aston Aston won the Nobel Prize for Chemistry in 1922, for his 1919 invention of the mass spectrograph, a new type of positive-ray apparatus which uses magnetic and electrostatic fields producing opposite deflections in the same plane to convert molecules into ions, then sorts the ions by to their mass-to-charge ratio. The mass spectroscope proved the existence of isotopes, allowed study of nuclear masses with great precision. -
Neils Bohr
bohrBohr refined Rutherford's model. he won the 1922 Nobel Prize in physics. Bohr proposed electrons: -orbit the nuculeus without losing energy; could move only in fixed orbits of specific energies. Electrons with low energy would orbit closer to the nuculeus while electrons with high energy orbit further from the nuculeus. Borh's model was based on mathmatics and experimentation. later, James Chadwick found evidence of another nuclear called the neutron. The neutron has no charge. -
James Chadwick
James Chadwick
His discovery helps clear the way for splitting the nuclei of even the heaviest atomic elements, making possible the development of the atomic bomb.
