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Democritus- Atomic Theory
Democritus proposes that all matter is made up of indivisible particles called Atoms -
Isaac Newton
Newton suggested that atoms are held together with forces. He also stated that "matter is formed of solid, massy impenetrable particles”. -
John Dalton
Dalton created the atomic theory:
1. all matter was composed of small indivisible particles called atoms
2. atoms of a specific element have unique characteristics and weight
3. there are three types of atoms: simple elements, compound (simple molecules), and complex molecules -
William Crookes- Cathode Rays
Crookes designed a tube where, virtually, no gas was present. The glow within the tube disappeared but one end of the tube was still glowing. An invisible ray was being emitted from the Cathode end called cathode rays -
George Johnstone Stoney
Introduced the term electron and estimated the charge to be that of a single hydrogen atom. -
J.J.Thomson
Thomson discovered that all atoms are made up of smaller particles. He originally called these particles 'corpuscles,' but they are now called electrons. This was determined when he studied Cathode Rays -
Max Planck
Planck explained that energy is not a continuous, flowing entity, but is carried in tiny, discontinuous units, which he named quanta. Each quantum's energy is equal to the frequency of radiation multiplied by the universal constant which Planck defined. -
Hantoro Nagaoka
He proposed a model in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings.The model made two predictions:
-a very massive nucleus (similar to saturn)
-electrons revolving around the nucleus, bound by electrostatic forces (similar to rings orbiting saturn) -
Ernest Rutherford- Godl Foil Experiment
He discovered the nucleus and developed a model of the atom. Electrons orbitted the central nucleus. He also discovered the proton through the Gold Foil Experiment. Not all paricles passed though the foil, some bounced back. Reasoning for positively charged particle:
1. Repelled by similar charge so nucleus must be positively charged
2. Few were deflected so it had to be smaller than an atom
3. particles were travelling so fast that only something with a large mass could deflect -
Robert Andrews Millikan
He determined the charge carried by an electron, using the "falling-drop method"; he also proved that this quantity was a constant for all electrons. -
Henry Moseley
Moseley experimented with the x-ray spectra and discovered the relationship of the wavelength and atomic number. Before, atomic numbers had been thought of as a number based on sequence of atomic weights. Moseley predicted a number of missing elements and their periodic numbers in the Periodic Table as well -
Niels Bohr- Quantum Theory
- an electron is a wave in a particular region of space.
- Confining electrons force them into a pattern which minimizes their energy.
- A place in the pattern is called a Quantum State and can hold only one electron
- Electrons are not found between states
- One one electron per quantum state
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Werner Heisenberg- Uncertainty Principle
It is not possible to know the definite position or velocity of a particle at quantum scales. "The quantum world is a world of statistics and probability, instead of exact certainty". -
James Chadwick
Chadwick discovered the neutron while originally working with Rutherford. When they were working together, they discovered that there was something else contributing to the atomic mass other than protons and electrons. Later on, Chadwick repeated experiments of other scientsist specifically looking for neutral particles with the same mass as a proton but with no charge -
Law of Conservation of Mass definition
law stating that every pure substance always contains the same elements combined in the same proportions by weight -
Electrons, Neutrons, Nucleus, and Protons, Definitions
Electrons- a negatively charged particle; located in the electron cloud
Neutron- A neutrally charged particle; located in the nucleus
Nucleus- The center of the atoms containg neutrons and protons
Protons- a positively charged particles; located in the nucleus -
Law of Definite Prooportions Definition
law stating that every pure substance always contains the same elements combined in the same proportions by weight -
Nuclear Model of Atom
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Spherical Model of Atom
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Bohr Model of Atom
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Plum Pudding Model
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Modified Nuclear Model of Atom
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bibliography
"Lab Aids." Lab Aids. N.p., n.d. Web. 5 Dec. 2013.
"Explore PBS." PBS. PBS, n.d. Web. 05 Dec. 2013.
Bio.com. A&E Networks Television, n.d. Web. 05 Dec. 2013.
