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Transcript
History of the Atom 7/6/2017 1 Atomic Theory: History 7/6/2017 Prominent scientists and their contributions to atomic theory Development of current atomic theory Show that science is a constantly changing field 2 Demicritius: 500 BC 7/6/2017 Suggested that matter consists of small indivisible particles called atoms. No one believed him. 3 Antoine Lavoisier: 1789 7/6/2017 Law of Conservation of Mass: Mass is not created or destroyed during a chemical reaction 4 1803 - John Dalton Dalton's Atomic Theory 1) Matter is composed of small indivisible particles called atoms 2) An element is composed entirely of one type of atom. The properties of all atoms of one element are identical and are different from those of any other element. 3) Atoms of different elements can physically mix together or chemically combine in simple whole number ratios to form compounds. 4) Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction. 7/6/2017 5 Dalton’s Theory 7/6/2017 6 Joseph Proust: 1806 7/6/2017 Law of Definite Proportions: A chemical compound always contains the same mass ratio of elements 7 Dmitri Mendeleev: 1869 7/6/2017 Published first Periodic table Arranged elements by atomic mass and allowed gaps where necessary Remarkable due to fact the he was not located close to scientific research 8 7/6/2017 9 Goldstein: 1886 7/6/2017 Discovered positive particles using a cathode ray tube Particles are called protons 10 J J Thomson: 1897 Cathode Ray Experiment Beam of electrons that flows from the cathode (-) to the anode (+). Discovered the electron in 1897. Discovered that most of the mass of an atom was positively charged Measured the Charge to Mass ratio ( e/m) of the electron. Nobel Prize in Physics in 1906 for his discovery of the electron Proposed “Plum Pudding Model” of the atom 7/6/2017 11 7/6/2017 12 Ernest Rutherford: 1898 7/6/2017 Identified two types of radiation emitted from Uranium. He calls them alpha and beta. In 1900, Paul Villard finds a third type which he calls gamma. During this same year, it is discovered that beta radiation is composed of electrons, and gamma radiation is very short wavelength electro-magnetic rays. 13 Types of Radiation 7/6/2017 14 Terms 7/6/2017 Radioactivity - the process by which materials give off unseen rays Radiation - the penetrating rays and particles emitted by a radioactive source Nuclear Stability: As the neutron/proton ratio deviates from 1:1, the nucleus becomes more unstable Half-life: time required for one-half of the nuclei of the radioisotope to decay to a new element 15 Marie Curie: 1902 7/6/2017 With her husband discovered radioactivity while studying radium and polonium 16 Ernest Rutherford: 1909 7/6/2017 Showed what happens to an element during radioactive decay. Constructed the first nuclear model of the atom, a cornerstone of present-day physics. 17 R A Milliken: 1909 7/6/2017 Oil drop experiment Measured the charge and mass of an electron Nobel prize in 1923 18 Oil Drop Experiment 7/6/2017 19 Ernest Rutherford: 1911 Gold Foil Experiment Theory: Shoot a stream of alpha ( + charged ) particles at a very thin layer of gold foil and they should easily pass through with only minor deflection. Results: Most particles passed straight through with no deflection Some were sharply deflected back from the gold foil Rutherford said, " It was almost as incredible as if you fired a 15 inch shell at a piece of tissue paper and it came back and hit you.“ 7/6/2017 20 7/6/2017 21 Gold Foil Experiment: Conclusions Most of the mass and all of the positive charge of the atom resides in a small region called the nucleus. The magnitude of the positive charge is different for different atoms. The charge of an atom is neutral. There are as many electrons outside the nucleus as there are protons in the nucleus. Electrons stay outside the nucleus unless acted upon by some force. 7/6/2017 22 Frederick Soddy: 1913 7/6/2017 Formulated the idea of isotopes Isotopes are atoms of the same element with different masses due to a different number of neutrons Note that the neutron has yet to be discovered 23 Rutherford: 1919 7/6/2017 Atoms can be transformed into elements by tampering with the nucleus Demonstrated that the nucleus of an atom could be breached 24 Neils Bohr: 1922 7/6/2017 Observed “line Spectra” and noticed that atoms do not emit energy continuously, but in precise quantities. Suggested that electrons are located in energy levels which keeps them from falling into the nucleus Predicted that specific energy levels hold only a certain # of electrons Proposed the model of electrons orbiting the nucleus of the atom similar to how the planets orbit the sun 25 7/6/2017 26 Bohr Model 7/6/2017 27 7/6/2017 28 Erwin Schrodinger: 1925 7/6/2017 Schrödinger’s equation is used to describe the state of electrons in the atom Develops Quantum Mechanical Model of the atom Quantum Mechanical Model of the atom describes the location of electrons defined by a 3 D mathematical probability region29 7/6/2017 30 James Chadwick: 1932 7/6/2017 Using alpha particles, discovered a neutral atomic particle with a mass close to that of the proton. This is what we know as a neutron. 31 Parts Of Atom Particle Symbol Charge Mass Electron Proton Neutron ep+ nO 1/1840 1 1 7/6/2017 11+ 0 32 Otto Hahn and Fritz Strassmann: 1938 7/6/2017 Discovered nuclear fission while working with uranium They would bombard it with neutrons and the nucleus would split into 2 parts 33 Fission Reaction 7/6/2017 34 Fission vs. Fusion 7/6/2017 Fission is splitting of the nucleus into 2 or more smaller atoms Fusion is joining 2 smaller nuclei into one new larger atom 35