???Everything we call real is made of things that cannot be regarded as real.??? -Niels Bohr. The Quantum Mechanical Model of the atom is the most current model of the atom. The model is based of quantum mechanics and finds the location of an electron in an atom. This model states that there are seven possible energy levels in an atom. The Quantum Mechanical Model does not have a defined path. All of its electrons are in a cloud structure.
John Dalton born September 6, 1766 was an early proponent of the Atomic Theory. The five main points of Daltons Atomic Theory are atoms of given elements are different from other elements can be distinguished from one another by their relative atomic weights. Two, all atoms of a certain element are identical. Three, atoms of one element combine with other atoms to form chemical compounds. Four, atoms cannot be created, divided into smaller particles or destroyed in the chemical process. Five, elements are made of atoms. Dalton determines that each element corresponds to a unique atom and develops chemical symbols based on atomic mass. Dalton??™s theory underwent some modifications from then to modern day. Those modifications included divisibility, destruction, radioactive decay, and isotopes of atoms and diatomicity of gases.
J.J Thomson discovered that atoms have particles known as electrons. His discovery came through his exploration on the properties of cathode rays. His experiments that he conducted before coming to the conclusion of his ???plum pudding model??? was the constructed Crookes tub with and electrometer to one side. The significance of the cathode rays was that the negative charge was inseparable from the rays. His second experiment where he investigated whether or not the rays could be deflected by the electric field. Thomson??™s third experiment before coming to his conclusion was the measurement of the mass to charge ratio. He came to the conclusion the atom was made up of corpuscles swarming in a sea of positive charge. This is known as the plum pudding model.
Ernest Rutherford was one of J.J Thomson??™s students and proved his plum pudding model incorrect. Rutherford??™s experiments consisted of testing the current bun. He fired energetic particles at foil then measured the deflection. Rutherford expected all of the particles to deflect but he discovered that most of the particles he shot at the foil were not deflected. Rutherford??™s new model ???the planetary model??? was that all of the positive charge was inside the nucleus. The flaw in Rutherford??™s model is that the charges are accelerating.
Neils Bohr contributed to the quantum mechanics. The Bohr model is the best approximate to the quantum mechanics. The Bohr model demonstrates that the region in the middle is known as the nucleus and the electrons orbit the nucleus. In Rutherford??™s model the electrons circle around the nucleus. Bohr??™s Model made restrictions on the movement of electrons. Bohr added a structure shell to Rutherford??™s model. Bohr concluded that an atom has specific energy levels to which electrons are fixed in a circular motion around the nucleus. He located approximately the location of the electrons in orbit surrounding the nucleus using quantum mechanics. Ground state electron of the element is the outer orbital. The outer orbital has the lowest energy state possible for the electron. The excited state is an electric current that excites the outer orbital electrons.
[Rutherford??™s Model][Bohr??™s Model]

???Those who are not shocked when they first come across quantum theory cannot possibly have understood it.???- Niels Bohr. Dalton had the first Atomic Theory and over time the theory has progressed from Thomson, Rutherford and Bohr. The changes between Bohr??™s model and the Quantum Mechanical Model were slight changes but they had a great impact. The Quantum Mechanical Model is the correct model that is used.
[Image: Dalton][Image: Thomson][Image: Rutherford][Image: Borh]

Works Cited
“Atomic Theory.” Mac OS X Server. Web. 06 Oct. 2010. .
“Goalfinder – Dalton Atomic Theory (Physics Animation in Flash ) – Animated Easy Science, Technology Software, Online Education, Medical, K12 Animation, & E-Learning.” Goalfinder Animated Science, Technology Software for Education Online, Technological Movies, Physics, Chemistry, Biology, Math Animation for Elearning and Posters for Schools and Colleges. Web. 06 Oct. 2010. .
“J. J. Thomson.” NNDB: Tracking the Entire World. Web. 06 Oct. 2010. .
“John Dalton.” NNDB: Tracking the Entire World. Soylent Communications. Web. 06 Oct. 2010. .
“John Dalton.” Wikipedia, the Free Encyclopedia. Web. 06 Oct. 2010. .
“The Rutherford Experiment.” Department of Physics and Astronomy. Web. 06 Oct. 2010. .
“The Rutherford Experiment.” Department of Physics and Astronomy. Web. 06 Oct. 2010. .
“The Rutherford Experiment.” Department of Physics and Astronomy. Web. 06 Oct. 2010. .
“Rutherfords Experiment and Atomic Model.” The Worlds of David Darling. Web. 06 Oct. 2010. .
Weisstein, Eric W. “Dalton, John (1766-1844) — from Eric Weissteins World of Scientific Biography.” ScienceWorld. Web. 06 Oct. 2010. .


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