Chapter 6 Electronic Structure of Atoms

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Chapter 6 Electronic Structure of Atoms

• SC 131 CHEM 1
• Chemistry The Central Science
• CM Lamberty

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Quantum Mechanics A Theory

• Smallness of atoms and subatomic particles
• Size of e- lt10-9 of 10-9 of a gram
• Speck of dust contains as many e- as there have
  been people on Earth since beginning
• Dtm chemical and physical properties
• Traditional observations not possible
• e- do not move in regular patterns
• e- observed behave differently than those not
  observed.
• Quantum-mechanical model
• Model to explain how e- exist in atoms and dtm
  properties
• Explain WHY some M, some NM, why noble gases are
  inert, etc.

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The Nature of Light

• Wave Nature of Light
• Properties of waves
• The Electromagnetic Spectrum
• Radio (low E) to Gamma rays (high E)
• Interference and Diffraction
• Ways waves may interact
• The Particle Nature of Light
• Photoelectric effect
• photons

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The Wave Nature of Matter

• Light is electromagnetic radiation
• Wave composed of oscillating mutually
  perpendicular electric and magnetic fields
• Speed of light (vacuum) 3.00x108 m/s

• Amplitude
• Vertical height of crest
• Determines the intensity of light

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The Wave Nature of Matter

• Wavelength
• Distance between adjacent crests
• Frequency
• Number of cycles passing a point in given period
  of time
• Cycles per second (s-1). 1 Hertz 1 cycle/s
• Frequency directly proportional to speed, inverse
  to wavelength

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Wavelength and Amplitude
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The Electromagnetic Spectrum

• Includes ALL wavelengths of EM radiation
• 10-15m (gamma) - 105m (radio waves)
• Short wavelength has greater E
• Gamma (g) rays
• Most energetic, shortest
• Produced by sun and stars and unstable atomic
  nuclei
• Damage to biological molecules
• X-rays
• Longer wavelength than gamma
• Pass through many substances that block visible
• Can damage biological molecules

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The Electromagnetic Spectrum

• Ultraviolet
• Component of sunlight for suntan/sunburn
• Carries enough E to damage biological mq
• excessive exposure skin cancer, cataracts
• Visible
• Violet (short l, high E) - red (longer l, lower
  E)
• Violet, blue, green, yellow, orange, red
• Causes certain mq in eye to change shape
  resulting in vision
• Color we see is reflected, others absorbed
• Infrared
• Heat from hot object
• Night vision goggles

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The Electromagnetic Spectrum

• Microwaves
• Longer wavelengths
• Used for radar and microwave ovens
• Efficiently absorbed by water and can heat
• Radio waves
• Longest wavelength
• Transmit signals responsible for FM and AM radio,
  cellular phones, TV, etc

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Interference and Diffraction

• Interference
• How waves add together
• Constructive or destructive
• Diffraction
• How waves bend to move around/though object
• Diffraction of light through 2 slits
• Interference pattern

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Interference and Diffraction
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The Particle Nature of Light

• Light initially thought of as wave
• Photoelectric effect
• Metals emit e- when light shines on them
• Series of tests did not follow EM theory
• Einstein packets of light E hn
• h is Plancks constant
• Photons
• Our name for packets of light
• Sometimes called quantum of light
• Light is lumpy
• Light is shower of particles each having e of hn

Wave-particle duality of light
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Atomic Spectroscopy Bohr Model

• Study of the EM radiation absorbed and emitted by
  atoms
• Atom absorbs E (heat, light, electricity) and
  remits the E as light
• Each element emit light of characteristic color
• Each with several distinct wavelengths
• Emission spectrum
• Each element has its own emission spectrum
• Discrete lines not continuous

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Atomic Spectroscopy Bohr Model
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Atomic Spectroscopy Bohr Model

• Johannes Rydberg
• Simple equation to predict wavelength of H
• 1/l R(1/m2-1/n2)
• Neils Bohr
• His model e- travel around nucleus in circular
  orbits.
• These orbits can exist only as specific fixed
  distances from nucleus
• E of each orbit was fixed or quantized
• Stationary states
• Only when e- made a transition that radiation
  emitted or absorbed

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The Wave Nature of Matter

• Louis de Broglie
• Wave nature of electrons
• Diffraction pattern
• de Broglie relation l h/mn
• Heisenberg
• Uncertainty Principle cannot simultaneously
  observe both the wave nature and the particle
  nature of the electron

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Quantum Mechanics and the Atom

• Schrodinger
• Orbital, probability distribution map showing
  where the electron is likely to be found
• Wave function
• Quantum Numbers used to specify each orbital or
  location of electron for an atom.

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Quantum Mechanics and the Atom

• Principle quantum number, n
• Integer that dtm overall size and E of orbital
• n 1,2,3
• Angular quantum number, l
• Integer that dtm shape of orbital
• l 0,1,2,(n-1)
• Magnetic quantum number, ml
• Integer that dtm orientation of orbital
• ml -l to l (-l, , -1, 0, 1,, l)

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Quantum Mechanics and the Atom
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Atomic Spectroscopy Explained
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The Shapes of Atomic Orbitals

• Shape important b/c covalent chemical bonds
  depend upon sharing of electrons and occupy these
  orbitals
• Shapes of the overlapping orbitals dtm shape of
  molecule
• Shape dtm primarily by l the angular momentum
  quantum number
• l0 s orbital
• l1 p orbital
• l2 d orbital
• l3 f orbital

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The Shapes of Atomic Orbitals

• s orbitals

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The Shapes of Atomic Orbitals

• p orbitals
• 2 lobes
• Node at nucleus
• Orbitals are orthogonal to one another

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The Shapes of Atomic Orbitals

• d orbitals
• 5 3d orbitals
• 4 are cloverleaf with 4 lobes
• 5th is 2-lobed with donut (see p. 266)

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Electron Configurations

• Electron configuration
• Ground state
• Electron spin and Pauli Exclusion Principle
• Direction of arrow represents electron spin
• Direction does not affect value
• Direction is quantized either up or down
• Spin Quantum Number, ms
• 1/2 (up) or -1/2 (down)

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Electron Configurations

• Pauli Exclusion Principle
• No two electrons can have the same four quantum
  numbers

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Electron Configurations

• Sublevel Energy Splitting in Multielectron Atoms
• E(s) lt E(p) lt E(d) lt E(f)
• Sheilding
• Effective nuclear charge

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Electron Configuration of Sulfur
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