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Electrons in Atoms

Ground/Excited States. Electrons in Atoms. Cathode Ray Tubes & Discovery of Electrons. Memory Jogger. Movie of cathode ray tube. Thomson ’ s Plum-Pudding Model. The positive charge is evenly smeared out. The negative charge is in bits – like chips. source. Rutherford ’ s Experiment - 1911.

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Electrons in Atoms

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  1. Ground/Excited States Electrons in Atoms

  2. Cathode Ray Tubes & Discovery of Electrons Memory Jogger Movie of cathode ray tube

  3. Thomson’s Plum-Pudding Model The positive charge is evenly smeared out. The negative charge is in bits – like chips. source

  4. Rutherford’s Experiment - 1911 source

  5. Problems with the Rutherford Model • Why don’t electrons crash into nucleus? • How are electrons arranged? • Why do different elements exhibit different chemical behavior?

  6. Bohr Model • Bohr - electrons in atom can have only specific amounts of energy NEW idea! • Each specific energy is associated with specific orbit • --electrons are restricted to these orbits • Bohr assigned quantum number (n) to each orbit • the smallest orbit (n= 1) • is closest to nucleus • has lowest energy • larger the orbit, more energy it has

  7. n=3 n=2 n=1 Bohr Diagram • Shows all the electrons in orbits or shells about the nucleus. Lowest energy (most stable) Highest energy (least stable)

  8. Orbit Max # of Electrons 1 2 2 8 3 18 4 32 n 2n2 Max Capacity of Bohr Orbits

  9. energy levels get closer together the farther away they arefrom nucleus Larger orbits can hold more electrons

  10. Bohr Model • Energy absorbed when electron: • moves to higher orbit (farther from nucleus) • Endothermic process • Energy released when electron: • drops to lower orbit (closer to nucleus) • Exothermic process

  11. Electron Transitions • If electron gains (absorbs) specific amount of energy • it can be excited to higher energy level • If electron loses specific amount of energy • it moves down to lower energy level

  12. Ground State vs. Excited State • Ground state: • Lowest energy state of atom • electrons in lowest possible energy levels • Configurations in Reference Tables are ground state • Excited state: • Many possible excited states for each atom • One or more electrons excited to higher energy level

  13. Ground State comes from the reference table Ar = 2-8-8 Total number of electrons = 18 Total number of protons = 18 Atomic Number = 18

  14. Excited State comes from the reference table 2-8-7-1 Total number of electrons = 18 Total number of protons = 18 Atomic Number = 18 Look on the periodic table for the atomic number 18, what is the ground state electron configuration

  15. Which principal energy level of an atom contains electron with the lowest energy? • A) n=1 • B) n=2 • C) n=3 • D) n=4

  16. What is total # of occupied principal energy levels in atom of neon in ground state? • A) 1 • B) 2 • C) 3 • D) 4

  17. Which atom in ground state has five electrons in its outer level and 10 electrons in its kernel? • A) C • B) Cl • C) Si • D) P Kernel electrons = inner electrons

  18. Which electron configuration represents atom in excited state? A) 2-8-2 • B) 2-8-1 • C) 2-8 • D) 2-7-1

  19. Which electron configuration represents atom of Li in an excited state? • A) 1-1 • B) 2-0-1 • C) 2-1 • D) 2-2

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