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Calvin Engstrom, Block D
This man of Abdera, Greece founded the study of atoms.
He found that atoms the smallest things in the universe after all.
His research added greatly to our understanding of the electron.
Democritus believed that if you cut an object in half, and then cut again and again, there would come a point where it couldn't be split. He proposed that at the point where it could not be divided again there was a single particle: an atom.
Democritus dubbed the particle an atom because it stemmed from the word "atomos" which means "indivisible." (The prefix "a" means "not" and the root "tomos" means "cut.")
British scientist Joseph John (J. J.) Thomson discovered that there are smaller particles within the atom itself. The particles that he investigated were negatively charged electrons, although they weren't dubbed this until well after his research. With this find, John Dalton's theory that atoms were indivisible was disproved.
Thomson's model of the atom was called the "plum pudding" model.
Thomson performed his experiments using a cathode-ray tube. Particles were fired between two plates, one positively and one negatively charged, and when those plates were charged, the beam was pulled toward the positive plate. Thus, Thomson came to the conclusion that these particles were both negatively charged and present within every type of atom.
Niels Bohr suggested that electrons don't haphazardly whirl around the nucleus, but instead they travel along certain paths or energy levels.
Bohr's model suggested several energy levels that the electrons could travel on, each one holding more electrons than the last.
440 BCE
England
Greece
1897
Present
Denmark
1913
Day
England
1803
England
1909
Austria/Germany
1926
Rutherford proposed that at the center of an atom was a miniscule, positively charged nucleus. He also concluded that atoms were mostly empty space with very tiny and very dense components, completely changing what was previously thought to be true.
His work completely redefined the atomic model.
The experiment which Rutherford drew his conclusions from involved aiming a beam of positively charged particles at a thin sheet of gold foil. Nearly surrounding this foil was material with a special coating that would glow where particles hit it. He found that some passed straight through, some were slightly deflected, and some bounced almost straight back.
These work of these men contributed significantly to the modern atomic model.
Rutherford's model suggested that there was actually a relatively vast amount of space between the parts of an atom. (Note: This diagram is not to his calculated scale, and neutrons were not discovered until 1932.)
He was one of the first pioneers of modern atomic theory.
Werner Heisenberg left, Erwin Schrödinger right
Dalton's theory consisted of three
main points:
He believed the atom to be round and smooth.
They found that Bohr was wrong, for electrons don't travel in definite paths. Instead, Schrödinger and Heisenberg said that the precise path of an electron is unpredictable. They suggested that there are places where they may be found called electron clouds.