Models+(VC)

indivisible solid sphere model

__http://hi.fi.tripod.com/timeline/images/indivisible_solid_sphere_model2.jpg__

This was the first model of an atom created by Leucippus and Democritus, two Greek philosophers that defined the atom. Their philosophical concept of an atom stated that an atom is “solid, small, and impenetrably hard”. The Greek word for atom also means indivisible.

electron cloud model __http://www.csmate.colostate.edu/cltw/cohortpages/viney_off/atom.jpg__

Bohr’s Electron cloud model was called such because electrons were not viewed as solid particle anymore but as “airy” hence the name electron cloud model. Bohr’s model of the atom shows the positively charged nucleus in the center and the negatively charged electrons orbitingthe nucleus. “Bohr stated that electrons can only exist at a certain, distance from the nucleus, or else it would loose its energy and be sucked into the protons.”

plum pudding model

__http://www.hcc.mnscu.edu/chem/V.08/plum_pudding_model.jpg__

J.J. Thomas, the founder of electrons, depicts an atom as a plum pudding that has negatively charged electrons uniformly arranged inside an atom. Surrounding the electrons is a ‘soup’ or cloud of positively charged protons. It was also known as the ‘chocolate chip cookie model’. This theory was before the discovery of the proton and the neutron and was proved incorrect by Ernest Rutherford.

rutherford’s nuclear atom __http://s3.amazonaws.com/readers/2009/02/25/1_4.jpg__

“Rutherford’s famous ‘gold foil experiment’ disproved J.J. Thomas’s plum pudding model of the atom. In the experiment, Rutherford fired an alpha particle towards a sheet of gold (gold foil). If Thomas’s theory was correct, all of the particles would go through the sheet of gold. Rutherford found that a few particles deflected or shot off the projected path after hitting something in the heart of the atom. This proved the existence of a nucleus in an atom, which led to the planetary cloud model of an atom. This mode described the position of electrons in circular orbits around the nucleus. The most common analogy to this theory would be the solar system: the electrons orbit around the nucleus of the atom, just as the planets of our solar system revolve around the sun.”

planetary model The Bohr Model is probably familiar as the "planetary model" of the atom illustrated in the adjacent figure that, for example, is used as a symbol for atomic energy. In the Bohr Model the neutrons and protons (symbolized by red and blue balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun (but the orbits are not confined to a plane as is approximately true in the Solar System). The adjacent image is not to scale since in the realistic case the radius of the nucleus is about 100,000 times smaller than the radius of the entire atom, and as far as we can tell electrons are point particles without a physical extent.

__http://craigjm.tripod.com/physics.html__