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Modern Theory of the Atom: Quantum Mechanical Model

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Modern Theory of the Atom: Quantum Mechanical Model Frequencies in Chemistry Electron Configuration & PT Principle Energy Levels Sublevels Orbitals hold 2 electrons ... – PowerPoint PPT presentation

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Title: Modern Theory of the Atom: Quantum Mechanical Model


1
Modern Theory of the AtomQuantum Mechanical
Model
2
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3
Recap of Bohr Model
  • electrons
  • particles moving in circular orbits with specific
    speed, position, energy
  • quantization of energy levels is imposed
  • electrons can move between energy levels
  • higher energy levels farther from nucleus
  • moving up to higher E level electron absorbs
    energy
  • moving down to lower E level electron emits
    light energy
  • Ground state
  • electrons located in lowest possible energy
    levels
  • closest can be to nucleus

4
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1924 De Broglie
  • Proposed this Idea
  • if light can show both particle and wave
    behavior, maybe matter can too

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9
2 kinds of waves
  • Traveling wave
  • wave not confined to given space
  • travels from one location to another
  • interrupted by hitting
  • boundary or another
  • wave
  • Standing wave
  • confined to given space (ends are pinned)
  • interference between incident reflected waves
  • at certain frequencies
  • certain points seem to be standing still
  • other points - displacement changes in regular way

10
  • Traveling Wave

11
  • Standing wave

12
DeBroglie Electron-Wave
wavelength describing electron depends on energy
of electron at certain energies, electron waves
make standing waves in atom wave does not
represent path of electron
13
Modern Theory
  • electron treated as wave
  • cannot specify both position speed of electron
  • can determine probability of electrons location
    in given region of space
  • Quantized energy levels arise naturally out of
    wave treatment

14
Bohr Model vs. Modern Theory
  • electron particle
  • e- path is orbit
  • holds 2n2 electrons
  • circular path
  • each orbit has specific energy
  • can find exact position/ speed
  • electron wave
  • e path is orbital
  • holds 2 electrons
  • not necessarily circular
  • each orbit has specific energy
  • probable location

15
Heisenberg uncertainty principle
  • Fundamentally impossible to know velocity
    position of particle at same time
  • Impossible to make observation without
    influencing system

16
What can orbitals do for us?
  • Physical structure of orbitals explain
  • Bonding
  • Magnetism
  • Size of atoms
  • Structure of crystals

17
Orbital Modern Theory
  • orbital term describes region where e- might be
    found
  • each orbital
  • specific energy specific shape
  • described by 4 parameters of wave function (like
    an address)
  • quantum numbers n, l, m, s

18
n principal quantum number
  • specifies atoms principal energy levels
  • whole number values 1, 2, 3, 4,
  • maximum electrons in any principal energy level
    2n2

19
l Describes sublevels
  • principal energy levels have sublevels
  • sublevels depends on principal energy level
  • 1st principal energy level has 1 sublevel
  • 2nd
    2
  • 3rd 3
  • 4Th 4
    , etc.

20
Naming sublevels
  • Sublevels are labeled by shapes
  • s, p, d, f
  • s orbitals spherical
  • p orbitals dumbbell shaped
  • d f orbitals more complex shapes

21
m 3rd quantum number
  • sublevels made up of orbitals
  • each sublevel has specific of orbitals

sublevel of orbitals
s 1
p 3
d 5
f 7
22
s orbital shapes
23
p orbital shapes
24
d orbital shapes
25
f orbital shapes
26
4th quantum number s
  • e- spin 2 possible values
  • clockwise and counter clockwise

27
Address for each electron
  • 4 quantum numbers
  • no 2 e- can
  • occupy the same space in atom
  • can have same 4 quantum numbers
  • therefore only 2 electrons per orbital
  • (Pauli exclusion principle)

28
principle energy level sublevels orbitals total e-
1 s 1 2
2 s 1 2
p 3 6
3 s 1 2
p 3 6
d 5 10
4 s 1 2
p 3 6
d 5 10
f 7 14
29
3rd principal energy level, 3 sublevels
2nd principal energy level, 2 sublevels s p
1st principal energy level, 1 sublevel s
Each box represents an orbital and holds 2
electrons
30
Order of fill Aufbau Principle
  • each electron occupies lowest energy orbital
    available
  • learn sequence of orbitals from lowest to highest
    energy
  • some overlap between sublevels of different
    principal energy levels

31
Aufbau Principle
  • Follow arrows
  • sequence of orbitals
  • 1s, 2s, 2p, 3s, 3p, 4s,
  • 3d, 4p, 5s, 4d,
  • exceptions do occur
    - half-filled orbitals
  • have extra stability
  • - magic is 8
  • 1s
  • 2s 2p
  • 3s 3p 3d
  • 4s 4p 4d 4f
  • 5s 5p 5d 5f
  • 6s 6p 6d 6f
  • 7s 7p

32
Electron Configurations
33
Compare Bohr Schrodinger
34
Frequencies in Chemistry
35
Electron Configuration PT
36
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37
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