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400
Democritus (460 BC- 370 BC)
The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms, there lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." -
John Dalton Atomic Modal
He based it upon :
1. Matter is made up of atoms that are indivisible and indestructible.
2. All atoms of an element are identical.
3. Atoms of different elements have different weights and different chemical properties.
4. Atoms of different elements combine in simple whole numbers to form compounds.
5. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged. -
J.J. Thomson Atomic Model
1 Atom is composed of positively charged substances
2 Electrons are embedded in the material and do not move this plus.
3 Electron masses is very small so that the entire mass of the atom creates a positively charged substances.
4 Atoms are spherical. -
Oil Drop Experiment
The oil drop experiment was an experiment performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron). The experiment entailed balancing the downward gravitational force with the upward drag and electric forces on tiny charged droplets of oil suspended between two metal electrodes.They found the charge of elctron. -
Gold Foil Experiment
Rutherford gold foil experiment was an experiment to prove the structure of the atom performed by Hans Geiger and Ernest Marsden in 1909,[1] under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester. The unexpected results of the experiment demonstrated for the first time the existence of the atomic nucleus, leading to the downfall of the plum pudding model of the atom, and the development of the Rutherford (or planetary) model. -
Rutherford Atomic Model
1-A small portion of the beam is broken and it was observed that a very small portion of the reflected: Then, in atomic + (positive), called the kernel loads were collected in a small volume.
2-The positive charge in the atom, so called core in the center of mass is concentrated in a very small volume.
3-Positively charged particles of atoms up electrons and atomic nuclei in the train of electron occupies a large portion of the volume. -
Bohr Atomic Model
1 A certain distance from the nucleus in an atom the electron moves in the orbit and the orbit of the angular momentum h/2p The exact multiples thereof. Each steady state has a constant energy.
2 Any stable energy level, electron moves in a circular orbit. These orbits are called energy levels or shells.
3 Steady state electron atoms found in one of the light (radiation) does not publish. However, from a higher energy level when it enters a lower energy level. -
Electron Cloud Model (Modern Atomic Model) in 20th century
1-According to the theory Electron Cloud occured molecules, atoms approach each other within the required bond before they occur molecule atom atomic orbitals found in the mingling of molecular orbitals stitute. After the formation of molecules from the atomic orbitals therefore descriptor.
2-How many orbitals in an orbit that is used to calculate the parameter n2. n, where "trajectory number" or "quantum number " is named. -
Sources
http://www.youtube.com/watch?v=eXdWlnBlncM
This youtube video for you!!!
These are the sources:
http://en.wikipedia.org/wiki/Electron_Cloud_Model
http://en.wikipedia.org/wiki/Bohr_model
http://en.wikipedia.org/wiki/Rutherford_model
http://en.wikipedia.org/wiki/Gold_foil_experiment
http://en.wikipedia.org/wiki/Plum_pudding_model
handout
http://en.wikipedia.org/wiki/Jj_thomson
http://en.wikipedia.org/wiki/John_Dalton#Atomic_theory
http://en.wikipedia.org/wiki/Democritus#Atomic_hypothesis
