EventsAristotle (and Plato) had the prevailing argument that matter is continuously and infinitely divisibleDemocritus named atoms “atomos” meaning indivisible. Democritus believed that atoms of the same element were alike and atoms different elements were different.
Artificial creation of radioactive isotopes with wife Irene.
Artificial creation of radioactive isotopes with wife Frederic.
Wave-particle duality of the electron
Postulated matter waves
Wavelength related to momentum
Matter waves in atoms are standing waves
1. Electrons only exist in certain allowed orbits
2. Within an orbit, the electron does not radiate
3. Radiation is emitted or absorbed when changing orbits
Robert Millikan (~1906)
Studied charged oil droplets in an electric field
Charge on droplets = multiples of electron charge
Charge + Thomson’s result gave electron mass
Reintroduced atomic theory to explain chemical reactions
1. All matter = indivisible atoms
2. An element is made up of identical atoms
3. Different elements have atoms with different masses
4. Chemical compounds are made of atoms in specific integer ratios
5. Atoms are neither created nor destroyed in chemical reactions
Law of Conservation of Matter- Matter is neither created nor destroyed in a chemical reaction. Atoms are rearranged.
Use the Cathode ray tube to describe negative particles called electrons.
Measured the charge to mass ratio.
Quantum Theory E=h x frequency
The Gold Foil Experiment Conclusions:
Atom is mostly empty space.
Nucleus is small, dense and positive.
Electrons are outside the nucleus.
Found the neutron which has no charge.
Introduced quantized energy
Light made up of quantized photons
Crooke Inventor of Cathode Ray Tube
Discovered transuranium elements
Established law of definite proportions
Father of nuclear chemistry. Discovered nuclear fission.
Built prototype of nuclear reactor. Helped to develop first atomic bomb.
Discovered radium and polonium with wife Marie.
Won Nobel Peace prize. Discovered radium and polonium with husband Pierre.
Quantum mechanics and particle physics. Helped in development of first atomic bomb.
Director of the Manhattan Project. "Father" of the first atomic bomb.
Inventor of the cyclotron. Uranium-isotope separation in the Manhattan Project.
First person to discover evidence of radioactivity
First discovered nuclear fission of uranium with Otto Hahn