* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download THE HISTORY OF THE ATOM Table of Contents Black Boxes
Mathematical formulation of the Standard Model wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Theory of everything wikipedia , lookup
Electric charge wikipedia , lookup
ALICE experiment wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Antiproton Decelerator wikipedia , lookup
Weakly-interacting massive particles wikipedia , lookup
Nuclear structure wikipedia , lookup
Grand Unified Theory wikipedia , lookup
Double-slit experiment wikipedia , lookup
Introduction to quantum mechanics wikipedia , lookup
Electron scattering wikipedia , lookup
ATLAS experiment wikipedia , lookup
Identical particles wikipedia , lookup
Standard Model wikipedia , lookup
Compact Muon Solenoid wikipedia , lookup
THE HISTORY OF THE ATOM Table of Contents Black Boxes Democritus Dalton’s Theory Thomson’s Electron Rutherford’s Nucleus Goldstein’s Protons Chadwick’s Neutron Atomic Symbols Black Boxes Black Boxes are anything that you cannot see inside Like a cell phone… Or a locked box… Or an atom… The Beginning of the Atom The ancient Greeks (back around 500BC) believed there only four elements: Earth Air Water Fire Democritus (460-370 B.C.) He also lived in ancient Greece but he believed differently He said that all matter was made up of particles that could not be divided into smaller particles He called these particles – Atoms 1 Aristotle (384-322 B.C.) Lived at the same time as Democritus but was more popular. People agreed with Aristotle and not Democritus. Alchemists (for over 1600 years) The oldest “Chemists”. Attempted to change common metals into gold. Created symbols for elements. Identified elements based on Democritus' theory. The Atomic Theory Democritus’ idea of the atom was largely ignored until an English schoolteacher did some experiments over 2000 years later, he was… John Dalton (1766-1804) “The Father of Modern Chemistry” Leading to his atomic theory… Dalton’s Atomic Theory All matter is made up of atoms Atoms are indestructible and cannot be divided into smaller particles (Atoms are indivisible) All atoms of one element are exactly alike, but they are different from atoms of other elements A given compound always has the same relative numbers and kinds of atoms. Atoms join in whole number ratios. Atoms are neither created nor destroyed in any chemical reaction. Dalton’s Model of the Atom Bowling Ball Theory: He believed the atom was a solid sphere An analogy to his atom would be… 2 Thomson’s Cathode Ray Tube Experiments and the Discovery of the Electron JJ Thomson (1856-1940) used the cathode ray tube to prove that the atom was made up of electrons But, what was that green light? Was it a light? Was it a particle? To test this, he brought a magnet close to the cathode ray tube to see what would happen. So, the magnet caused the cathode ray to move. What does that tell us? Would a magnet affect a light from a flashlight? (you could try this at home) Probably not. Therefore, the cathode ray must be a particle! Thomson also noticed… That the cathode ray was coming out of the negative end (cathode) of the tube and going toward the positive end (anode) Negative end Positive end Therefore, because opposites attract, he concluded that the cathode ray must be negative He called these particles… ELECTRONS! The discovery would alter Dalton’s model of the atom because now there is something inside it But, in addition to the negatively charged electrons, there must be something giving it a positive charge because the overall charge of the atom is neutral (not negative) Let’s look at Thomson’s model of the atom… Thomson’s Plum Pudding Model of the Atom He believed the atom was made of positively charged stuff with negatively charged particles scattered throughout. Why the “plum pudding” model? What is “plum pudding”? 3 Plum Pudding is an English dish sort of like bread pudding with raisins in it. Rutherford and the Nucleus In 1908, Ernest Rutherford performed the Gold Foil Experiment. In it, he shot alpha particles (very small, very dense, very fast particles) at a thin layer of gold foil. He expected all of the alpha particles to go straight through It would be like if you were shooting bullets at a cake…all of the bullets (or alpha particles) would go straight through the cake (or gold foil atoms) gold foil detector screen alpha particles Alpha particles source Thomson’s Atom Alpha particles But, what he found was this… or Did you notice how most of the alpha particles went straight through but a very tiny amount were deflected at odd angles? That could only happen if there was something very tiny in the atom that was dense enough to deflect the alpha particles. Like this… To recap the Gold Foil Experiment Rutherford proved that an atom: was mostly empty space with a very small, very dense, positively charged nucleus in it. Rutherford’s Planetary Model of the Atom 4 He believed the atom was made of a tiny positively charged nucleus with negatively charged particles orbiting it Or… If the atom were Soldier Field, the nucleus would be a pea on the fifty – yard line Other important discoveries… In 1886, Goldstein discovered the proton (which is located in the nucleus) In 1932, Chadwick discovered the neutron (also located in the nucleus) Bohr’s Model of the Atom Modern Theory of the Atom. Orbits in quantum levels. (1920) Although the diagram suggests that electrons travel in circular orbits, this is a simplification and is not actually the case. Feeling overwhelmed? "Teacher, may I be excused? My brain is full." Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem 5