Development of the atom!!!!!!!!!!!

The atomic theory, was proposed in the 5th century. B.C. by the Greek philosophers Leucippus and Democritus and was adopted by the Roman Lucretius. But it was ignored for many centuries. Interest in the atomic theory was revived during the 18th century following work on the nature and behavior of gases.

1. Who were the main characters in the development of the atom?

Modern atomic theory begins with John Dalton. He held that all the atoms of an element are of exactly the same size and weight and are in these two respects unlike the atoms of any other element. He stated that atoms of the elements unite chemically in simple numbers to form compounds. The best evidence for his theory was the experimentally verified law of simple multiple proportions, which gives a relation between the weights of two elements that combine to form different compounds.

Evidence for Dalton's theory also came from Michael Faraday's law of electrolysis. A major development was the periodic table, devised simultaneously by Dmitri Mendeleev and J. L. Meyer, which arranged atoms of different elements in order of increasing atomic weight so that elements with similar chemical properties fell into groups. By the end of the 19th century it was generally accepted that matter is composed of atoms that combine to form molecules.

In 1911, Ernest Rutherford developed the first explanation of the structure of an atom. Using alpha particles emitted by radioactive atoms, he showed that the atom consists of a central core, called the nucleus, and negatively charged particles called electrons that orbit the nucleus. There was one serious obstacle to acceptance of the nuclear atom. According to classical theory, as the electrons orbit around the nucleus, they are continuously being accelerated, and all accelerated charges radiate electromagnetic energy. which, they should lose their energy and spiral into the nucleus.

This difficulty was solved by Niels Bohr (1913), who applied the quantum theory developed by Max Planck and Albert Einstein to the problem of atomic structure. Bohr proposed that electrons could circle a nucleus without radiating energy only in orbits for which their orbital angular momentum was an integral multiple of Planck's constant, divided by 2π. The discrete spectral lines emitted by each element were produced by electrons dropping from allowed orbits of higher energy to those of lower energy, the frequency of the photon of light emitted being proportional to the energy difference between the orbits.

Around the same time, experiments on x-ray's by H. G. J. Moseley showed that each nucleus was characterized by an atomic number, equal to the number of unit positive charges associated with it. By rearranging the periodic table according to atomic number rather than atomic weight, a more systematic arrangement was obtained. The development of quantum mechanics during the 1920s resulted in a satisfactory explanation for all phenomena related to the role of electrons in atoms and all aspects of their associated spectra. With the discovery of the neutron in 1932 the modern picture of the atom was complete.

2. Why were they vital to the development?

Each one of them put in there own thought and ideas into the atom at different time in life. They were all from different parts of the world at different times and different technology. With all of there ideas it eventually brought us to what the atom is today.

3. What made them different if anything?

They all didnt think the one before them was right, they believed there was more to the atom and kept testing ideas to make a better understanding of the atom and how it works. They all had different technology at the time they were alive making some things more testable and possible than others

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