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400 BCE
Democritus
Democritus was a Greek philosopher. He said that if a stone was cut into smaller pieces that at some point the stone would be small the piece would be indivisible, he called these indivisible pieces "atomos" (atoms). He thought that matter was made of these atomos (atoms), he believed that they come in all different shapes and sizes, his idea was rejected for about 2,000 years. -
John Dalton
Dalton had four major points 1. matter is composed of small indivisible particles called atoms 2. the atoms of the same element are identical and aroma of different elements are not identical 3. atoms of different elements combine in whole-number ratios to form compounds 4. chemical reactions are rearranged of atoms (atoms cannot be created nor destroyed). He had evidence to support his theory. -
J.J Thomsom
J.J Thomson began experimenting with Cathode ray tubes, he used the tubes to shoot negatively charged particles toward the positive end of the cathode ray. He found out that the negatively charged particles went to the positive side and away from the negative side of the tube. His conclusion was that Cathode ray is composed of negatively charged particles, the particles are part of the atom, the subatomic particles can be found within atoms of all elements. -
Ernest Rutherford
Rutherford used think sheets of gold foil with fast-moving alpha particles, the results were most of the particles were undeflected, a small portion bounced off at large angles, or was redirected back towards the source. He concluded that all of the positive charge and the majority of the mass of the atom must be concentrated in every small space called the nucleus. -
Niels Bohr
He states that the electrons moved in fixed orbits of specific energy, the energy of the electron depends on the location and size of the orbit. He said that electrons can jump from one orbit to another by losing or gaining energy, lost energy gives off a certain color of light depending on how much energy was lost. Each atom has a different electron makeup so each light given off an element is different. -
Erwin Schrodinger
His model is an advancement of Bohr's model. He discovered that identifying the specific location of the electrons was not possible and that you could only find the location through the probability of finding them in an area around the nucleus. The areas where electrons are supposed to be found are called electrons cloud or orbitals.