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Democritus "Atom"
In 465 BC, Democritus discovered the atom. His mentor origionally came up with this theory, but Democritus adopted it. He conducted an experiment (which you can still do) to find out about the atom. He took a simple seashell and broke it in half. Then, he took one half and broke it again, and he did this over and over again until he was left with a powder. He then took the smallest piece from the powder and attempted to break it, but could not. Thus, created his model. -
Dalton
Dalton's theory at the time, was correct. He disproved Democritus and stated that "Matter is made up of tiny particles, called atoms, that cannot be divided into smaller pieces, and cannot be destroyed." Democritus only knew of the basics and Dalton built on that. -
Dalton "Billard Ball"
Dalton investigated pressure and other properties of gases, and he inferred that gases must consist of tiny, individual particles in constant, random motion. He also researched properties of compounds and found that a given compound is always comprised of of same elements with same number ratio and different compounds consist of different elements & ratios. Dalton reasoned that this could happen only if elements are made of seperate, discrete particles not to subdivided. -
JJ Thomson
Thomson's model was correct and accurate for his time because even though he lacked the information on positively charged particles, he had all the correct information he could find at the time of discovery. Therefore making his model correct, until proven wrong by another scientist's discovery. -
JJ Thomson "Plum Pudding Model"
Thomson discovered electrons by experimenting with cathode ray tubes. He demonstrated that they were negatively charged & he studied positively charged particles in neon gas. He realized the accepted model of an atom did not represent the - and + charged particles & proposed a model that looked like plum pudding. - electrons represented raisins & dough contained + charge. Model explained negative particles but didn't recognize positvie particles. -
Rutherford "Rutherford's Model"
Rutherford tested Thomson's hypothesis by devising his 'gold foil' experiment. He reasoned that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. He shot high velocity alpha particles (helium nuclei) at an atom then there would be very little to deflect the alpha particles. He decided to test this with a thin film of cold atoms. As expected alpha particles went right through the gold foil but to his amazement a few alpha particles rebundled! -
Rutherford
These deflections were my consistent with Thomson's model. Rutherford was forced to discard the Plum Pudding model & reasoned that the only way the alpha particles could be deflected backwards was if most of the atom mass in an atom was concentrated in nucleus. He this developed the planetary model of the atom which put all the protons in nucleus & electrons orbited around nucleus like plums around the sun. -
Bohr
4) energy & frequency of light emitted/absorbed is given by difference between orbit energies.
Bohr was able to explain stability of atoms as well as the emissior spectrum of hydrogen. According to Bohr's model only certain are possible. These energies naturally lead to the explanation of the hydrogen atom spectrum. -
Bohr "Bohr's Model"
Rutherford asked Bohr to work on it because there were some problems with the model. Bohr discovered two problems. He realized that the problems were connected and after some thought, he came up with the Bohr model of the atom. It consists of 4 principals l. 1) electrons assume-only certain orbits around nucleus. Orbits are stable & 'stationary' orbits. 2) each orbit has energy associated with. 3) light is emitted when electron jumps from a higher orbit to lower orbit & absorbed when it jumps. -
Schrodinger "Quaintent Model"
SchrodingerErwin Schrödinger built upon the thoughts of Bohr yet took them in a new direction. He developed the probability function for the Hydrogen atom (and a few others). The probability function basically describes a cloud-like region where the electron is likely to be found. It can not say with any certainty, where the electron actually is at any point in time, yet can describe where it ought to be. Clarity through fuzziness, is one way to describe the idea.
