S: Atomic Theory Timeline
FC: By: Rachael Lonce and Shannon Cline | Atomic Theory Timeline
1: 400 B.C.- Democritus | Democritus was the first person to come up with the atomic theory. Democritus proposed that all matter is composed of atoms.
2: Dalton’s Atomic Theory proposed that chemical elements are composed of a unique type of atom, and that these atoms differ in their masses. Dalton composed a chart of chemical symbols based on their atomic mass. Dalton also came up with the development of the laws of definite and multiple proportions, which he said that a chemical combination of different elements occurs in simple numerical ratios by weight . (http://abyss.uorgeon.edu/~js/21st_century_science/lectures/lec05.html). | 1800s- Dalton's Atomic Theory
3: -Proposed that electricity was made of discrete negative particles he called electrons. -Acknowledged for his contribution to developing the theory of electrons by H.A. Lorentz , in his Nobel Lecture in 1902. | 1874 George Johnstone Stoney
4: 1879 - J.J Thomson
5: J.J Thomson 1897- J.J Thomson discovered the electron; J.J discovered the electron when he was working on the cathode ray tube. In previous experiments with the cathode ray tube, when an electric current was passed threw a vacuum tube, a stream of “glowing material” could be seen. No one could explain why there would be glowing material when the electric current was streamed threw. Thomson put a positively charged electric plate near the vacuum tube and found that the “glowing material” would move toward the plate. J.J Thomson found that the glowing material were actually atoms, and that these atoms were negative, causing the glowing material to move toward the positively charged electric plate. These negatively charged atoms were then named electrons, making J.J. Thomson the founder of the electron. | Thomson Atomic theory was proposed in 1904, which he called his “Plum Pudding Model”. In Thomson’s “Plum Pudding Model” the pudding is positively charged fluid, scattered within the fluid are electrons, or as Thomson called them the “plums”. Ernest Rutherford disproved J.J Thomson’s model in 1909 with his Gold foil experiment. Rutherford founded the nucleus making Thomson’s theory incorrect.
6: 1886 Eugen Goldstein | Discovered canal rays (also known as anode rays) and showed that they were positively charged particles (ions) produced from gases. 1886 he used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.
7: Performed an oil drop experiment to determine the charge and the mass of an electron to be 1.602 x 10-19 C and 9.11 x 10-28 g respectively. He made a machine which would drip of oil into a chamber where he could watch. The droplets carried the electrons he needed. The voltage changed when the drop entered which then he could calculate the charge of the electron. Millikan received a Nobel prize for Physics in 1923. | 1909 Robert Andrews Millikan
8: 1911- Rutherford | Came up with the gold foil experiment. In this experiment Rutherford shot alpha particles moving at high speeds towards a gold sheet. The particles were mostly made up of protons and neutrons, making the overall charge positive. When these particles were shot, most of them went straight threw the gold sheet. Those particles that went threw showed that the atom is really empty space, the atom was hitting the gold sheet where the gap was between the nucleus and the electron. Some of the other particles seem to shot at angles, this was because of other atoms passing they were being attracted by their electrons. Then very few particles would hit the gold sheet and bounce back. This was happening because the atoms of these particles were hitting the nucleus head on and being shot back. This is how the nucleus of an atom was discovered.
9: Henry Moseley is credited with the application X-ray spectra to study atomic structure. Thanks to Moseley's development, it resulted in more accurate positioning of elements on the periodic table. Moseley founded that the x-ray emissions and wavelengths of elements went hand-in-hand with these elements atomic number. The finding of Isotopes of a element showed that the weight of an element wasn't the only thing important in determining an element, but also it's atomic number. Thanks to Henry Moseley, the periodic table now has elements arranged by their atomic number. | 1913-Henry Moseley
10: Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons. He did all his work around the year 1911 Made a model that shows rings around the nucleus with electrons on the rings. In 1922, Bohr was awarded the Nobel Prize in physics "for his services in the investigation of the structure of atoms and of the radiation emanating from them" | 1922 Niels Bohr
11: 1932 James Chadwick | James Chadwick discovered the Neutron. Chadwick found that because Rutherford showed that the atom is tightly packed together by the nucleus, the protons of the small atom would repel each other. The Neutrons would help stop the protons from repelling each other and stabilize the nucleus. Chadwick also found the neutrons not to have any electric charge, that they are electrically neutral. This is so because the number of protons and electrons are the same and cancel out one another.
18: A Smile As Sweet As Spring
20: April Showers Bring May Flowers
23: it's always spring in a mother's heart
24: spring: a. The season of the year, occurring between winter and summer, during which the weather becomes warmer and plants revive, extending in the Northern Hemisphere from the vernal equinox to the summer solstice and popularly considered to comprise March, April, and May. b. A time of growth and renewal.
26: "be like the flower, turn your face to the sun." - Kahlil Gibran | It's a beautiful day, don't let it get away.
28: "Blossom by blossom the spring begins"
29: It's a beautiful day, don't let it get away.
31: A Smile As Sweet As Spring
32: Nothing Is So Beautiful As Spring