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Unformatted text preview: HISTORY OF THE ATOMIC HISTORY MODEL MODEL Chapt e r s 4, 5. 1, + 25 4, SCIENTIST Democritus: MODEL The Greek Model (460 BC – 370 BC) • 400 BC: Matter can’t be divided forever; there must be a smallest piece (atomos) • Atoms are indestructible, indivisible, & the fundamental units of matter Atom: smallest particle of an element that retains the properties of that element. - no electric charge, electrically neutral • No experiments to test his theories SCIENTIST John Dalton: MODEL Dalton’s Model (1766 – 1844) Dalton’s Atomic Theory (1803): All elements are composed of atoms that are submicroscopic indivisible particles. Atoms of the same elements are identical & atoms of different elements are different. Atoms of different elements can physically mix together or chemically combine w/one another to form simple wholenumber ratios to form compounds. Chemical reactions occur when atoms are separated, rearranged or joined. Atoms of one element can never be changed into atoms of another element. SCIENTIST SCIENTIST J.J. Thomson: MODEL Thomson’s Model (1856-1940) (1856-1940) • • • • • 1897: Used cathode ray tube to discover electrons Cathode ray: glowing beam which travels from the cathode(-) to the anode(+). the - are composed of electrons - are attracted to positive metal plate Atoms had negatively charged particles ELECTRON: negatively charged subatomic particle negatively • not the original name (corpuscle) “Plum Pudding” Model Plum • (chocolate chip cookie) (watermelon) • - a ball of positive charge containing electrons ball Thomson’s ATOMIC Model Thomson’s POSITIVE CHARGE ELECTRONS EMBEDDED WITHIN Cathode Ray Tube: http://www.chem.uiuc.edu/demos/cathode.html http:// Robert Millikan (1868-1953) Oil Drop Experiment (1916) Oil Determined the Determined charge and mass of an electron of The mass is The 1/1840 of the mass of a hydrogen atom (unit)? (unit)? SCIENTIST SCIENTIST Ernest Rutherford: +++ +++ • • MODEL Rutherford’s Model (1871-1937) (1871-1937) Empty Space + Nucleus Gold Foil Experiment (1911) Discovered that most of atom’s mass is located in the Discovered positively charged nucleus positively NUCLEUS: center of the atom composed of PROTONS & NEUTRONS PROTONS NEUTRONS is 99.9% of the atom’s mass a marble in a football stadium http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf Rutherford’s Gold Foil Experiment: Rutherford’s (1911) (1911) http://micro.magnet.fsu.edu/electromag/java/rutherford/ Gold Foil Experiment: Rutherford Gold PROTON: positively charged subatomic particle PROTON positively discovered by Eugen Goldstein (1850-1930) discovered 1886: put holes in cathode and saw rays traveling 1886: in the opposite direction (canal rays) in NEUTRON: subatomic particle with no charge particle discovered by Sir James Chadwick (1891-1974) (1891-1974) 1932: mass is nearly equal to proton (1 amu) Thomson & Rutherford proved Thomson Dalton’s Theory incorrect: ATOMS ARE DIVISIBLE ATOMS http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf SCIENTIST MODEL SCIENTIST MODEL Niels Bohr: The Bohr Model (1885-1962) Electrons +++ +++ Energy Levels Electrons move in definite orbits around Electrons the nucleus (planets around the sun) the 1913: PLANETARY MODEL Electrons are a part of energy levels Electrons energy located certain distances from the nucleus nucleus Energy Levels: region around the nucleus where the electron is likely to be moving. electron a lladder that isn’t equally spaced adder further the distance, closer the spacing the higher the energy level the farther it is from the the nucleus nucleus Electrons can jump from 1 energy level to another. Electrons Quantum Energy: amount required to move an amount electron from its present energy level to the next higher one. level SCIENTIST SCIENTIST Erwin Schrodinger Erwin • • • • MODEL Quantum Mechanic Model (1887-1961) Quantum 1926: Wave mechanics-mathematical Probable location of electron Cloud Shaped Propeller blade Subatomic particles: Electrons, Protons, & Neutrons Atomic Number: Number of Protons in the nucleus Whole number written above chemical symbol Ex: Hydrogen=1(P) Oxygen=8(P) Hydrogen=1(P) Subatomic particles: Subatomic Electrons, Protons, & Neutrons Electrons, Atomic Number: Number of Protons in the Number nucleus nucleus • Whole number written above chemical symbol Ex: Hydrogen=1(P) Oxygen=8(P) Hydrogen=1(P) Atomic Mass #: Sum of Protons Sum + Neutrons Ex: Carbon Mass #12 = 6(P) + 6(N) Carbon Oxygen Mass #16 = 8(P) + 8(N) A.Mass # (#P + #N) - Atomic # (#P) = A.Mass #N) Atomic #Neutrons #Neutrons LETS HAVE SOME PRACTICE LETS Element Symbol Element Name Mass Number (P+N) Atomic Number (P) Atomic Number (P) 6 C Carbon 12 12 6 Mass Number (P+N) C WHAT GIVES AN ATOM ITS IDENTITY? IDENTITY? • • • Isotope: Same # of Protons, Same different # of Neutrons different Different Mass Number Same Atomic Number Chemically alike Ex: Carbon-12 Mass #12 = 6(P) + 6(N) Carbon-12 Carbon-13 Mass #13 = 6(P) + 7(N) Atomic Mass for isotopes of Carbon = 12.01 amu SO, WHAT GIVES AN ATOM ITS IDENTITY? IDENTITY? # of protons gives the atom its identity # of electrons determines the chemistry of of the atom of # of neutrons only changes the mass of of the atom the DO NOW DO There are 3 isotopes for Oxygen O-16 O-17 O-18 1. Write the shorthand chemical symbol for Write all three isotopes all 12 6C O-16 16 8 O O-17 O-17 17 8 O O-18 18 8 O Average Atomic Mass Average 80% tests ---50 20% homework---100 What is your average? (50+100)/2=75, not the case, (50+100)/2=75, tests are weighted more tests .80x50= 40 .20x100=20 60 is your grade Average Atomic Mass Average Two isotopes of carbon are C-12 the abundance is 98.89% C-13 the abundance is 1.11% What is the average atomic mass (12+13)/2=12.5 C-12: (98.89%/100) x 12=11.87 C-13: (1.11%/100) x 13=0.14 11.87+0.14=12.01amu Average Atomic Mass Average Do questions #23 & #24 on page 117 DO NOW DO Determine the # of protons, neutrons, & Determine electrons for the 4 isotopes of zinc: electrons Protons Neutrons Electrons 64 30 Zn 30 34 30 66 30 Zn 30 36 30 Zn 30 37 30 Zn 30 40 30 67 30 70 30 DO NOW DO Element X has two natural isotopes with Element mass 10.012 amu and a relative abundance of 19.91%. The isotope with mass 11.009 amu has a relative abundance of 80.09%. abundance 1. Calculate the atomic mass of this element 1. (show all work) and then name this element. element. Nuclear Chemistry The study of changes in matter that originate in atomic nuclei What makes a nucleus unstable? Too many or Too few neutrons relative to the # of protons The nuclei of unstable isotopes gain stability by undergoing changes Changes that Radioactive Isotopes Undergo Alpha α particle Beta β particle Release of helium nuclei Rutherford’s Gold Foil Exp. Release of an electron from the breaking apart of a neutron in an atom Gamma γ ray Release of photons (light energy) What can they penetrate? Alpha α =almost nothing Beta β = somethings Inhalation (radon) Open wounds Can’t go through skin, paper, wood, plastic, lead, concrete Skin & paper Can’t go through wood, plastic, lead, concrete Gamma γ = a lot of stuff Skin, paper, & wood Can’t go through lead or concrete http://www.furryelephant.com/player.php?subject=physics&jumpTo=re/2Ms4 Half-Life Unstable isotopes have a rate of decay, known as half-life Uses of Radioactive Isotopes Carbon dating (pg. 806, 814,815) Geiger counter (pg 817) Film Badge (817) Agriculture tracers (pg 818) Treating Cancer (pg 819) ...
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