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John Dalton-Atomic Theory
His Theory:
. Matter is made up of indivisible atoms.
2. All atoms of an element are identical.
3 Atoms are neither created nor destroyed.
4 Atoms of different elements have different weights and chemical properties.
5 Atoms of different elements combine in simple whole numbers to form compounds. -
Michael Faraday
He setup a pair of metal plates sealed in a glass tube. The tube was filled with a gas, and the metal plates were connected to a series of batteries. As the pressure of the gas decreased, the gas began to glow. Julius Plucker (1858) noticed that only one end emitted light. He also changed the position of the patch of glass that glowed by bringing a magnet close to the tube. Conclusion: The effect of the magnetic field as evidence that whatever produced this glow was electrically charged. -
Johannes Hittorf
He found that when a solid object was placed between the cathode and anode, a shadow was cast on the end of the tube across from the cathode. Conclusion: Some beam or ray is given off by the cathode - subsequently called the tubes cathode-ray tubes. -
William Conrad Roentgen
He discovered x-rays while using cathode-ray tubes. Found that x-rays could pass through solid objects. -
J.J. Thomson-Rasin Pudding Model Of Atom
He found that cathode rays could be deflected by an electric field. He showed that cathode "rays" were actually particles. He found the charge to mass ratio of the particles to be approximately 108 Coulomb (C) per gram. He found out that there was a same charge to mass ratio regardless of metal used for cathode/anode or gas used to fill the tube. Thomson also came up with a Raisin Pudding Model of the atom. -
Ernest Rutherford
Rutherford studied absorption of radioactivity. -
Einstein-Theory Of Relativity
Albert Einstein developed a theory about the relationship of mass and energy. The formula, E=mc[2], is clearly the most famous outcome from Einstein's special theory of relativity. -
Rutherford updates Thomson's Raisin Pudding Model of the atom
Rutherford studied the deflection of alpha particles as they were targeted at thin gold foil sheets. Most of the alpha particles penetrated straight through, however few were deflected at slight angles. Even fewer (only about 1 in 20,000) were deflected at angles over 90. He then came up with a new model of the atom. -
Robert Millikan - Oil-drop Experiment
J.J. Thomson had previously hypothesized that the mass of a single electron was at least 1000 times smaller than that of the smallest atom. Millikan measured the charge on an electron with his oil-drop apparatus. An "atomizer" from a perfume bottle sprayed oil or water droplets into the sample chamber. Some of the droplets fell through the pinhole into an area between two plates (one positive and one negative). This middle chamber was ionized by x-rays. Particles that did not capture any elect -
A. Van Den Broek
He suggested that the positive charge on atoms should be compared to their atomic numbers, not their atomic weights. At the time, atomic number (Z) only specified an element's location on the periodic table. Today, the atomic number is, by definition, the number of protons in an atom. -
H. G. J. Moseley
Moseley studied the frequencies of the x-rays given off by cathode-ray tubes when electrons strike the anode. Found that there was a relationship between the frequencies (v) of the x-rays given off by the cathode-ray tube and the atomic number of the metal used to form the anode. Moseley argued that the frequencies of the x-rays should depend on the charge on the nucleus emitting these x-rays. Therefore, the atomic number was equal to the positive charge (charge on the nucleus) of an atom. -
Rutherford's "Proton" and "Neutron"
Rutherford proposed the name "proton" for the positively charged particles in the nucleus of an atom. At the same time, he also proposed that the nucleus also contained electrically neutral particles which accounted for the remaining mass of the atom. He called this yet unknown particle the "neutron". -
James Chadwick
James proved that neutrons, neutral particles in the nucleus that made up approximately half the mass of an atom, did exist. -
Enrico Fermi-Splitting Of The Atom
Enrico Fermi became the first physicist to split the atom. His research pioneered the nuclear age.
