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Physical Setting/Chemistry

Physical Setting/Chemistry. Models of the Atom Br. Jabreal. Aim: How can chemical properties of elements be explained at the atomic level?. Do Now: What is a chemical property of an element? What was Rutherford’s model of the atom like?. The Development of Atomic Models.

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Physical Setting/Chemistry

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  1. Physical Setting/Chemistry Models of the Atom Br. Jabreal

  2. Aim: How can chemical properties of elements be explained at the atomic level? • Do Now: What is a chemical property of an element? What was Rutherford’s model of the atom like?

  3. The Development of Atomic Models • Rutherford’s model explained only simple properties of atoms • Could not explain chemical properties of elements • E.g. Why do metals or compounds of metals give off characteristic colors when heated in a flame? • Why do objects glow, first appearing dull red, then yellow, then white, when heated at higher and higher temperatures?

  4. Explaining what leads to chemical properties of elements requires a model that better describes behavior of electrons in an atom

  5. The Bohr Model • Niels Bohr (1885-1962) • Danish Physicist and student of Rutherford • Made adjustments to Rutherford’s model to explain new discoveries of how energy of atom changes when it absorbs or emits light • Proposed that electrons found only in specific circular paths, or orbits, around the nucleus • Each orbit has a fixed energy. Fixed energies an electron can have called energy levels. • Quantum is energy req. to move from one level to next

  6. Energy levels like rungs in a ladder • Electrons can climb up and down energy levels like a person can climb the rungs of a ladder • Electrons can only stand at the energy levels, not in between – just like you can’t stand in between the rungs of a ladder • Higher the energy level the further from the nucleus

  7. Bohr model gave results in agreement with hydrogen atom, but failed in many ways to explain energies absorbed and emitted by atoms with more than one electron

  8. Quantum Mechanical Model • Erwin Schrodinger devised mathematical equation to describe behavior and movement of electrons • Restricts electrons to energy levels like Bohr model did, however does not involve exact path electron takes around the nucleus • Quantum mechanical model determines allowed energy levels an atom can have AND how likely it is to find the electrons in various locations

  9. Do Now: How did Bohr adjust Rutherford’s atomic model? What is the difference between the quantum mechanical model and Bohr’s planetary model?

  10. Quantum mechanical model describes motion of an electron similar to that of a rotating propeller • It’s a blur, and you can’t be certain exactly where that propeller is within that blur in a given time

  11. In the quantum mechanical model/Wave Mechanical Model(Electron Cloud Model), the probability of finding an electron within a certain volume of space surrounding the nucleus is represented by a cloud. The cloud is more dense where the probability of finding an electron is high.

  12. Atomic Orbitals • Atomic Orbital: region of space in which there is a high probability of finding an electron • Each energy level has a number of corresponding atomic orbitals with different shapes

  13. Different atomic orbitals are denoted by letters. The sorbitals are spherical and the porbitals are dumbbell-shaped

  14. Each orbital can hold up to 2 electrons • What’s the maximum number of electrons in energy levels 1-4?

  15. Common Regents Question • Which term is defined as the region in an atom where an electron is most likely to be located? • Nucleus • Orbital • Quanta • Spectra

  16. Common Regents Question • Which term is defined as the region in an atom where an electron is most likely to be located? • Nucleus • Orbital • Quanta • Spectra

  17. Common Regents Question • According to the wave-mechanical model of an atom, an orbital is a region of the most probable location of • An alpha particle • A gamma ray • An electron • A proton

  18. Common Regents Question • According to the wave-mechanical model of an atom, an orbital is a region of the most probable location of • An alpha particle • A gamma ray • An electron • A proton

  19. Self-Assessment • Rutherford’s Planetary Model could not explain (1) any properties of elements (2) The chemical properties of elements (3) The distribution of mass in an element (4) The distribution of positive and negative charges in an atom

  20. Self-Assessment • Rutherford’s Planetary Model could not explain (1) any properties of elements (2) The chemical properties of elements (3) The distribution of mass in an element (4) The distribution of positive and negative charges in an atom

  21. Bohr’s model of the atom proposed that electrons are found • Embedded in a sphere of positive charge • In fixed positions surrounding the nucleus • In circular orbits at fixed distances from the nucleus • Orbiting the nucleus in a single fixed circular path

  22. Bohr’s model of the atom proposed that electrons are found • Embedded in a sphere of positive charge • In fixed positions surrounding the nucleus • In circular orbits at fixed distances from the nucleus • Orbiting the nucleus in a single fixed circular path

  23. What is the lowest-numbered principal energy level in which porbitals are found?

  24. Homework • Skim Section 5.1 • Section 5.1 Assessment • Questions 1, 3, 5

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