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History Of Atom Notes

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  • 1. Models of the AtomModels of the Atom September 24September 24thth & 25& 25thth , 2009, 2009
  • 2. Ancient GreeceAncient Greece 300 BC in Greece300 BC in Greece School of thought that matter is made upSchool of thought that matter is made up of tiny indivisible, invisible, indestructible,of tiny indivisible, invisible, indestructible, fundamental units of matter called atomsfundamental units of matter called atoms (means “that which cannot be divided”)(means “that which cannot be divided”) Democritus of Abdera most well knownDemocritus of Abdera most well known atomist.atomist. Did no experimentsDid no experiments No proofNo proof PhilosopherPhilosopher
  • 3. 1770s1770s Antoine Lavosier made observations and didAntoine Lavosier made observations and did experiments resulting in the Law ofexperiments resulting in the Law of Conservation of MassConservation of Mass Law of Conservation of MassLaw of Conservation of Mass Matter cannot be createdMatter cannot be created or destroyedor destroyed Mass of materials before theMass of materials before the chemical reaction is the samechemical reaction is the same mass after the reactionmass after the reaction
  • 4. 1799- Joseph Proust1799- Joseph Proust Showed that the proportion by mass of theShowed that the proportion by mass of the elements in a compound is always the same (COelements in a compound is always the same (CO vs. COvs. CO22)) Now called the Law of Definite ProportionsNow called the Law of Definite Proportions Part of our definition of a chemical - any substancePart of our definition of a chemical - any substance with a definite compositionwith a definite composition
  • 5. 1808- John Dalton1808- John Dalton English School TeacherEnglish School Teacher Wanted to learn in what ratios differentWanted to learn in what ratios different elements combineelements combine Based on the Greek idea of the atomBased on the Greek idea of the atom Atoms were tiny indestructible particlesAtoms were tiny indestructible particles Which clay model is this?Which clay model is this?
  • 6. Dalton’s Atomic TheoryDalton’s Atomic Theory 1.1. All matter is made of indivisible, invisible, andAll matter is made of indivisible, invisible, and indestructible particles called atomsindestructible particles called atoms 2.2. Atoms of the same element are identicalAtoms of the same element are identical 3.3. Atoms of different elements differ in their physical andAtoms of different elements differ in their physical and chemical propertieschemical properties 4.4. Atoms of different elements combine in simple wholeAtoms of different elements combine in simple whole number ratios to form compoundsnumber ratios to form compounds 5.5. Chemical Reactions occur when atoms are separated,Chemical Reactions occur when atoms are separated, joined or rearranged. Atoms of one element are NEVERjoined or rearranged. Atoms of one element are NEVER changed into atoms of another element.changed into atoms of another element.
  • 7. Problems with Dalton’s ModelProblems with Dalton’s Model Atoms are not indestructible, they are made ofAtoms are not indestructible, they are made of smaller parts like protons, neutrons, electrons andsmaller parts like protons, neutrons, electrons and quarksquarks Atoms of the same element are notAtoms of the same element are not completelycompletely identical, isotope exist with different massesidentical, isotope exist with different masses Atoms of the same element can combine with eachAtoms of the same element can combine with each otherother Atoms can “turn into” other elements throughAtoms can “turn into” other elements through nuclear decay (though there are byproducts)nuclear decay (though there are byproducts)
  • 8. 18971897 Sir J.J.ThomsonSir J.J.Thomson Proposed that the cathodeProposed that the cathode ray formed in the tube is aray formed in the tube is a stream of negativelystream of negatively charged particlescharged particles Atoms have parts that areAtoms have parts that are negatively chargednegatively charged Since atoms are neutral,Since atoms are neutral, they must also havethey must also have positively charged areaspositively charged areas Gave rise to the plumGave rise to the plum pudding model of the atompudding model of the atom
  • 9. 1909 -Ernst Rutherford1909 -Ernst Rutherford Experimented with the positively charged particleExperimented with the positively charged particle He figuredHe figured Atoms have no chargeAtoms have no charge Electrical charges are properties of matterElectrical charges are properties of matter Electrical charges exist in single whole numberElectrical charges exist in single whole number units + or - (no fractions)units + or - (no fractions) Electrical Charges cancel each other, thereforeElectrical Charges cancel each other, therefore a + and a - together = neutral atoma + and a - together = neutral atom
  • 10. Rutherford’s modelRutherford’s model Key Idea -NUCLEAR ATOMKey Idea -NUCLEAR ATOM All of the mass of the positive particles (protons)All of the mass of the positive particles (protons) is at the center region of the atomis at the center region of the atom Center region called the NUCLEUSCenter region called the NUCLEUS Electrons surround the nucleus in a “cloud”Electrons surround the nucleus in a “cloud”
  • 11. Plum PuddingPlum Pudding vsvs NuclearNuclear Which clay models are these?Which clay models are these?
  • 12. Bohr’s Atom- 1913Bohr’s Atom- 1913 There are certain energy levels thatThere are certain energy levels that mathematically allow the electron to stay inmathematically allow the electron to stay in the cloud (not crash into the nucleus)the cloud (not crash into the nucleus) Key idea - There are certain circular ORBITS inKey idea - There are certain circular ORBITS in which an electron can travel around thewhich an electron can travel around the nucleus without losing energynucleus without losing energy The farther away from the nucleus, the higherThe farther away from the nucleus, the higher the energy levelthe energy level
  • 13. What do weWhat do we know now??know now?? All models are not exactly correct, but they lead toAll models are not exactly correct, but they lead to further understanding and discoveryfurther understanding and discovery All have important key ideasAll have important key ideas Atoms are made up of subparticlesAtoms are made up of subparticles Atoms are divisible, but not by ordinary chemical meansAtoms are divisible, but not by ordinary chemical means Atoms of elements can vary (isotopes)Atoms of elements can vary (isotopes) Electrons reside in ORBITALS, not orbitsElectrons reside in ORBITALS, not orbits
  • 14. What happens when you change…What happens when you change… Protons: Since the number of protons is the same as theProtons: Since the number of protons is the same as the atomic number, protons are what define an element.atomic number, protons are what define an element. If you change the protons you change the elementIf you change the protons you change the element Neutrons: The neutrons add to the mass of the element.Neutrons: The neutrons add to the mass of the element. If you change the neutrons you change the mass ofIf you change the neutrons you change the mass of the element (make an isotope)the element (make an isotope) Electrons: The electrons balance the charge of theElectrons: The electrons balance the charge of the protons.protons. If you change the electrons you change the charge ofIf you change the electrons you change the charge of the element (make an ion)the element (make an ion)
  • 15. Quotes about atomsQuotes about atoms FromFrom A Short History of Nearly EverythingA Short History of Nearly Everything by Bill Brysonby Bill Bryson ““protons give an atom itsprotons give an atom its identity, electrons itsidentity, electrons its personality” p. 140personality” p. 140 ““if an atom were expandedif an atom were expanded to the size of a cathedral,to the size of a cathedral, the nucleus would be onlythe nucleus would be only about the size of a fly- but aabout the size of a fly- but a fly many thousands of timesfly many thousands of times heavier than the cathedral”heavier than the cathedral” p. 141p. 141