Atomic theory contributions

Dalton was the first scientist to help contribute to the atomic theory. He based his thought process off of Democritus, an ancient Greek philosopher, who stated that at one point you will not be able to break down matter anymore, he called this basic building block an atom (meaning not divisible). Democritus believed that everything around us such as metal, water, and wood were atoms, but Dalton believed and proved that it could be more basic than that. He started thinking of compounds such as water, salt, or wood; that they could be a number of atoms combined to make that product. He also believed that atoms such as carbon, gold, and hydrogen could not be broken down. Dalton made some rules according to his theory:
1. All elements are made of atoms.
2. All atoms of the same element are identical, but different from atoms of another element.
3. Atoms can physically mix or chemically combine, in simple whole number ratios.
4. Chemical reactions are caused by atoms rearranging. No new atoms are created or destroyed.
Dalton’s model of the atom had some problems explaining why atoms would combine or bond, which leads to the next great scientist. J. J. Thomson discovered electrons from his experiment using a cathode ray tube experiment. He shot an electric current/ ray through a plate of metal in tube filled with gas. He found that some particulate or small pieces of matter (not energy or light) gathered at the end of the tunnel, the positively charged end. So he deducted that it being attracted to the positive side must be negative. He put objects in the way and these small pieces of matter would warm up the object and push it away with some force. He found the mass of negative particles was about 2000 times smaller than a H atom. He experimented with different types of metal plates and different gases and it was the same reaction every time. So in conclusion Thomson found that these tiny negatively charged particles, called electrons, are in everything, are part of atoms, and changed the model of the atom. Thomson’s model of the atom shows the whole area being positive stuff with some negative electron mixed throughout it. Leading to our next great experiment performed by Rutherford. Rutherford believed in Thomson’s model, for the atom, and experimented to prove that it was correct. He used a radioactive substance as a laser, in a lead casing with a small hole (for it to shoot out), and pointed it at gold foil. He set up a screen around it so that he could track where the particles went. According to the model it should have shot right through but he found that most went through and some particles shot back at low and sometimes high angles. So he concluded from this experiment that every atom has very dense positive material at the center, called the nucleus, and atoms are mostly empty space. Unfortunately Rutherford did not know how to arrange the electrons and guessed that they would orbit around the nucleus the same way planets orbit around the sun. This theory didn’t work because mathematicians found that after a period of time the electrons would crash into the nucleus. Bohr came up with the missing piece in Rutherford’s theory: electrons have energy levels. Compared to rungs of a latter the electrons are on a step (energy level) but not in the space between. However he was still having trouble explaining the location of the electrons. He thought that the electrons were particles, but Schrodinger thought of them more as a wave. Most scientists liked the wave theory because it was easy to calculate and understand the location and momentum of the electrons. But with the Uncertainty Principle (you cannot find momentum and position accurately at the same time because electrons are always moving) they could combine theories stating that electrons are particles that behave like a wave. Thus the Quantum Mechanical Model shows that there is a 90% chance that an electron is in the clouded/ shaded area of the atom. Schrodinger came up with the QMM and determined that electrons do not have a fixed path around the nucleus. All in all the theories and progression of time lead to what we know about atoms and the way they look thanks to Dalton, Thomson, Rutherford, Bohr, and Schrodinger.