III. Quantum Model of the Atom

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III. Quantum Model of the Atom

• Ch. 5 - Electrons in Atoms

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A. Electrons as Waves

• Louis de Broglie (1924)
• Applied wave-particle theory to e-
• e- exhibit wave properties

QUANTIZED WAVELENGTHS
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A. Electrons as Waves
QUANTIZED WAVELENGTHS
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A. Electrons as Waves
EVIDENCE DIFFRACTION PATTERNS
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A. Electrons as Waves

• Diffraction (def) bending of a wave as it
  passes by the edge of an object
• Interference (def) when waves overlap (causes
  reduction and increase in energy in some areas of
  waves)

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B. Quantum Mechanics

• Heisenberg Uncertainty Principle
• Impossible to know both the velocity and position
  of an electron at the same time

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B. Quantum Mechanics

• Schrödinger Wave Equation (1926)
• finite of solutions ? quantized energy levels
• defines probability of finding an e-

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B . Quantum Mechanics

• Schrodinger wave equation and Heisenberg
  Uncertainty Principle laid foundation for modern
  quantum theory
• Quantum theory (def) describes mathematically
  the wave properties of e- and other very small
  particles

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B. Quantum Mechanics

• Orbital (electron cloud) each holds 2 e-
• Region in space where there is 90 probability of
  finding an e-

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C. Quantum Numbers

• Four Quantum Numbers
• Specify the address of each electron in an atom

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C. Quantum Numbers

• 1. Principal Quantum Number ( n ) positive whole
  integers
• Main Energy level
• Size of the orbital
• n2 of orbitals in the energy level

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Principle Quantum Number

• As n increases, the e- energy and distance from
  the nucleus increases
• More than 1 e- can have the same n value

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C. Quantum Numbers

• 2. Angular Momentum Quantum ( l )
• Energy sublevel
• Shape of the orbital
• Values 0 to (n-1)

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C. Quantum Numbers
If l equals Then orbital shape is
0 s
1 p
2 d
3 f
Principle quantum followed by letter of
sublevel designates an atomic orbital
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C. Quantum Numbers

• 3. Magnetic Quantum Number ( ml )
• Orientation of orbital
• Specifies the exact orbitalwithin each sublevel

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C. Quantum Numbers
px
py
pz

• Values are -l 0 l

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C. Quantum Numbers

• Orbitals combine to form a spherical shape.

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C. Quantum Numbers

• 4. Spin Quantum Number ( ms )
• Electron spin ? ½ or -½
• An orbital can hold 2 electrons that spin in
  opposite directions.

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C. Quantum Numbers

• Pauli Exclusion Principle
• No two electrons in an atom can have the same 4
  quantum numbers.
• Each e- has a unique address

1. Principal ? 2. Ang. Mom. ? 3. Magnetic
? 4. Spin ?
energy level sublevel (s,p,d,f) orbital electron
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C. Quantum Numbers

• n of sublevels per level
• n2 of orbitals per level
• Sublevel sets 1 s, 3 p, 5 d, 7 f

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Feeling overwhelmed?
Read Section 5-2!