chapters 4, 5.1, + 25 history of the atomic model
TRANSCRIPT
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Chapters Chapters
4, 5.1, + 254, 5.1, + 25
HISTORY OF THE ATOMIC HISTORY OF THE ATOMIC MODELMODEL
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SCIENTIST MODELDemocritus: 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
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SCIENTIST MODEL
John Dalton: 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 whole-number 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.
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SCIENTISTSCIENTIST MODELMODEL
J.J. Thomson:J.J. Thomson: Thomson’s ModelThomson’s Model
(1856-1940)(1856-1940)
• 1897: Used cathode ray tube to discover electrons1897: Used cathode ray tube to discover electrons• Cathode ray:Cathode ray: glowing beam which travels from glowing beam which travels from
the cathode(-) to the anode(+).the cathode(-) to the anode(+).
- are composed of electrons- are composed of electrons
- are attracted to positive metal plate- are attracted to positive metal plate• Atoms had negatively charged particlesAtoms had negatively charged particles• ELECTRONELECTRON: : negatively charged subatomic particlenegatively charged subatomic particle
• not the original name (corpuscle)not the original name (corpuscle)• ““Plum Pudding” Model Plum Pudding” Model
• (chocolate chip cookie) (watermelon)(chocolate chip cookie) (watermelon)
• - - a ball of positive charge containing electronsa ball of positive charge containing electrons
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Thomson’s ATOMIC ModelThomson’s ATOMIC Model
ELECTRONSEMBEDDED WITHIN
POSITIVE CHARGE
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Cathode Ray Tube: Cathode Ray Tube:
http://www.chem.uiuc.edu/demos/cathode.htmlhttp://www.chem.uiuc.edu/demos/cathode.html
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Robert Millikan (1868-1953) Robert Millikan (1868-1953) Oil Drop Experiment (1916)Oil Drop Experiment (1916)
Determined the Determined the charge and mass charge and mass of an electronof an electron
The mass is The mass is 1/1840 of the 1/1840 of the mass of a mass of a hydrogen atom hydrogen atom (unit)?(unit)?
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SCIENTISTSCIENTIST MODELMODELErnest Rutherford:Ernest Rutherford: Rutherford’s ModelRutherford’s Model (1871-1937)(1871-1937)
• Gold Foil Experiment (1911)Gold Foil Experiment (1911)• Discovered that most of atom’s mass is located in the Discovered that most of atom’s mass is located in the
positively charged nucleuspositively charged nucleus
NUCLEUSNUCLEUS:: center of the atom composed of center of the atom composed of PROTONSPROTONS & & NEUTRONSNEUTRONS
is 99.9% of the atom’s massis 99.9% of the atom’s mass a marble in a football stadiuma marble in a football stadium
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swfhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Empty Space
++++++ + Nucleus
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Rutherford’s Gold Foil ExperimentRutherford’s Gold Foil Experiment: : (1911)(1911)
http://micro.magnet.fsu.edu/electromag/java/rutherford/ http://micro.magnet.fsu.edu/electromag/java/rutherford/
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Gold Foil ExperimentGold Foil Experiment: Rutherford: Rutherford
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PROTONPROTON: : positively charged subatomic particlepositively charged subatomic particle discovered by Eugen Goldstein (1850-1930)discovered by Eugen Goldstein (1850-1930) 1886: put holes in cathode and saw rays traveling 1886: put holes in cathode and saw rays traveling in the opposite direction (canal rays)in the opposite direction (canal rays)NEUTRONNEUTRON:: subatomic subatomic particle with no chargeparticle with no charge discovered by Sir James Chadwick discovered by Sir James Chadwick (1891-1974)(1891-1974) 1932: mass is nearly equal to proton (1 amu)1932: mass is nearly equal to proton (1 amu)
Thomson & Rutherford proved Thomson & Rutherford proved Dalton’s Theory incorrect: Dalton’s Theory incorrect: ATOMS ARE DIVISIBLEATOMS ARE DIVISIBLE
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swfhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
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SCIENTISTSCIENTIST MODELMODEL
Niels Bohr: The Bohr Model (1885-1962)Niels Bohr: The Bohr Model (1885-1962)
Electrons move in definite orbits around Electrons move in definite orbits around the nucleus (planets around the sun)the nucleus (planets around the sun)
1913: PLANETARY MODEL1913: PLANETARY MODEL Electrons are a part of Electrons are a part of energy levelsenergy levels
located certain distances from the located certain distances from the nucleusnucleus
Electrons
++++++ Energy
Levels
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Energy LevelsEnergy Levels: region around the nucleus where the: region around the nucleus where the
electron is likely to be moving.electron is likely to be moving. a ladder that isn’t equally spaced a ladder that isn’t equally spaced further the distance, closer the spacingfurther the distance, closer the spacing the higher the energy level the farther it is from the the higher the energy level the farther it is from the
nucleusnucleus
Electrons can jump from 1 energy level to another.Electrons can jump from 1 energy level to another.
Quantum EnergyQuantum Energy: amount required to move an : amount required to move an
electron from its present energy electron from its present energy
level to the next higher one.level to the next higher one.
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SCIENTISTSCIENTIST MODELMODEL
Erwin Schrodinger Erwin Schrodinger Quantum Mechanic Model (1887-1961)Quantum Mechanic Model (1887-1961)
• 1926: Wave mechanics-mathematical1926: Wave mechanics-mathematical• Probable location of electronProbable location of electron• Cloud ShapedCloud Shaped• Propeller bladePropeller blade
Subatomic particles: Electrons, Protons, & NeutronsSubatomic particles: Electrons, Protons, & Neutrons Atomic NumberAtomic Number: Number of Protons in the nucleus: Number of Protons in the nucleus Whole number written above chemical symbolWhole number written above chemical symbol ExEx: : Hydrogen=1(P)Hydrogen=1(P) Oxygen=8(P)Oxygen=8(P)
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Subatomic particlesSubatomic particles: : Electrons, Protons, & NeutronsElectrons, Protons, & Neutrons
Atomic NumberAtomic Number: Number of Protons in the : Number of Protons in the nucleusnucleus
• Whole number written above chemical symbolWhole number written above chemical symbolExEx: : Hydrogen=1(P)Hydrogen=1(P) Oxygen=8(P)Oxygen=8(P)
Atomic Mass #Atomic Mass #: Sum of Protons : Sum of Protons ++ Neutrons NeutronsExEx: : Carbon Mass #12 = 6(P) + 6(N)Carbon Mass #12 = 6(P) + 6(N)
Oxygen Mass #16 = 8(P) + 8(N)Oxygen Mass #16 = 8(P) + 8(N)A.Mass # (#P A.Mass # (#P + + #N)#N) - - Atomic # (#P)Atomic # (#P) = = #Neutrons#Neutrons
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LETS HAVE SOME PRACTICELETS HAVE SOME PRACTICE
6
CCarbon
12
Atomic Number (P)
Mass Number(P+N)
Element Symbol
Element Name
126
Mass Number(P+N)
Atomic Number(P)
C
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WHAT GIVES AN ATOM ITS WHAT GIVES AN ATOM ITS IDENTITY?IDENTITY?
IsotopeIsotope: Same # of Protons, : Same # of Protons,
different # of Neutronsdifferent # of Neutrons• Different Mass NumberDifferent Mass Number• Same Atomic NumberSame Atomic Number• Chemically alikeChemically alike
ExEx: : Carbon-12 Mass #12 = 6(P) + 6(N)Carbon-12 Mass #12 = 6(P) + 6(N)
Carbon-13 Mass #13 = 6(P) + 7(N)Carbon-13 Mass #13 = 6(P) + 7(N)
Atomic Mass for isotopes of Carbon = 12.01 amuAtomic Mass for isotopes of Carbon = 12.01 amu
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SO, WHAT GIVES AN ATOM ITS SO, WHAT GIVES AN ATOM ITS IDENTITY?IDENTITY?
# of protons gives the atom its identity# of protons gives the atom its identity
# of electrons determines the chemistry # of electrons determines the chemistry of the atomof the atom
# of neutrons only changes the mass of # of neutrons only changes the mass of the atomthe atom
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DO NOWDO NOW
There are 3 isotopes for OxygenThere are 3 isotopes for OxygenO-16O-16O-17O-17O-18O-18
1.1. Write the shorthand chemical symbol for Write the shorthand chemical symbol for all three isotopesall three isotopes
CC12 6
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O-16 O O-16 O
O-17 OO-17 O
O-18 OO-18 O
16 8
17 8
18 8
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Average Atomic MassAverage Atomic Mass
80% tests ---5080% tests ---50
20% homework---10020% homework---100
What is your average?What is your average?
(50+100)/2=75, not the case, (50+100)/2=75, not the case,
tests are weighted moretests are weighted more
.80x50= 40 .20x100=20.80x50= 40 .20x100=20
60 is your grade60 is your grade
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Average Atomic MassAverage Atomic Mass
Two isotopes of carbon areTwo isotopes of carbon areC-12 the abundance is 98.89%C-12 the abundance is 98.89%C-13 the abundance is 1.11%C-13 the abundance is 1.11%What is the average atomic massWhat is the average atomic mass(12+13)/2=12.5(12+13)/2=12.5C-12: (98.89%/100) x 12=11.87C-12: (98.89%/100) x 12=11.87C-13: (1.11%/100) x 13=0.14C-13: (1.11%/100) x 13=0.1411.87+0.14=12.01amu11.87+0.14=12.01amu
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Average Atomic MassAverage Atomic Mass
Do questions #23 & #24 on page 117Do questions #23 & #24 on page 117
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DO NOWDO NOWDetermine the # of protons, neutrons, & Determine the # of protons, neutrons, &
electrons for the 4 isotopes of zinc:electrons for the 4 isotopes of zinc:
ProtonsProtons NeutronsNeutrons ElectronsElectrons
ZnZn 3030 3434 3030
ZnZn 3030 3636 3030
ZnZn 3030 3737 3030
ZnZn 3030 4040 3030
6430
6630
6730
7030
ProtonsProtons NeutronsNeutrons ElectronsElectrons
ZnZn
ZnZn
ZnZn
ZnZn
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DO NOWDO NOW
Element X has two natural isotopes with Element X has two natural isotopes with mass 10.012 amu and a relative mass 10.012 amu and a relative abundance of 19.91%. The isotope with abundance of 19.91%. The isotope with mass 11.009 amu has a relative mass 11.009 amu has a relative abundance of 80.09%.abundance of 80.09%.
1. Calculate the atomic mass of this element 1. Calculate the atomic mass of this element (show all work) and then name this (show all work) and then name this element.element.
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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
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Changes that Radioactive Isotopes Undergo
Alpha α particle Release of helium nuclei Rutherford’s Gold Foil Exp.
Beta β particle Release of an electron
from the breaking apart of a neutron in an atom
Gamma γ ray Release of photons (light energy)
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What can they penetrate? Alpha α =almost nothing
Inhalation (radon) Open wounds Can’t go through skin, paper, wood, plastic, lead, concrete
Beta β = somethings 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
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Half-Life
Unstable isotopes have a rate of decay, known as half-life
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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)