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Nicole Hesson

on 28 January 2011

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Transcript of Atoms

Atoms History Democritus developed the idea of atoms around 460 B.C. He thought "If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further?" His ideas were dismissed for more than 2000 years. In the 1800s, John Dalton (an English chemist) performed experiments that showed matter was made of "lumpy particles" (atoms). In 1897, J.J. Thomson discovered electrons. He also proposed a model for the structure of the atom. His model is called the "plum pudding model". Ernest Rutherford used positively charged particles as "bullets" and fired them at a very thin piece of gold foil. He expected them to barge through the gold atoms, but they did not. He concluded that the positive charge of an atom must be concentrated at the center.

He called the positive particles protons. This led to a new model for the atom. However, there were a few problems with Rutherford's model. In 1912, Niels Bohr came up with a theory that would allow Rutherford's model to work. "Here's some rules that seem impossible, but they describe the way atoms operate, so let's pretend they're correct and use them." - Bohr's point of view Bohr's rules stated that 1. electrons must be orbiting the nucleus in a particular level, or shell. and 2. energy must be given out when electrons fall from a high shell to a low shell. This model wasn't perfect either, and a whole ton of scientists have added their 2 cents. Sommerfeld, Pauli,
Schrodinger, Born,
Heisenberg, Chadwick
Anderson, Dirac,
Yukawa, Powell, Feynman,
Schwinger, Itiro, Gell-Mann,
Ne'man, and others... We still use Bohr's basic model. Today, we don't know the EXACT location of an electron...but we know where they are likely to be found. We call this an electron cloud. Structure of an Atom For our purposes, atoms have 3 main parts. Protons Neutrons Electrons are found in the nucleus have a positive charge The nucleus is the center of the atom. are found in the nucleus have a neutral charge An atom is stable as long as the number of protons equals the number of electrons. have a negative charge are found orbiting the nucleus And now you're ready to explore atoms on your own. To orbit means to make a circular path around an object.
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