Chapter 5 Notes

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Chapter 5 Notes

• Electrons in Atoms

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5.1 Light and Quantized Energy

• Rutherfords nuclear model lacking
• didnt account for electron arrangement
• couldnt explain why diff. elements behave diff.
• Elements emit visible light when heated in a
  flame

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Wave Nature of Light

• Electromagnetic radiation form of energy that
  exhibits wavelike behaviors as it travels through
  space (visible light, microwaves, X-rays)
• Speed
• Wavelength (?) distance b/t two crests or
  troughs
• Frequency (ƒ) number of waves that pass a given
  point in one second measured in Hz
• Amplitude height of wave from origin to crest
  or trough

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Electromagnetic Spectrum

• Encompasses all forms of electromagnetic
  radiation

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Particle Nature of Light

• Max Planck
• Explained emission of light by heated objects
  (red hot )
• Quantum minimum amount of energy gained/lost by
  an atom
• Equantum h?
• Photoelectric effect (explained by Einstein)
• Photoelectrons emitted from metals surface
• Electromagnetic radiation is both wavelike
  particle - like
• Photon particle of electromagnetic radiation w/
  no mass that carries a quantum of energy

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Atomic Emission Spectra

• Set of frequencies of the electromagnetic waves
  emitted by atoms of an element
• An elements fingerprint

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5.2 Quantum Theory and the Atom

• Neils Bohr
• Danish physicist
• Proposed quantum model that explained why
  emission spectra were discontinuous

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Bohr Model of the Atom

• Ground state lowest allowable energy state of
  an atom
• Electrons orbit the nucleus in certain energy
  levels (circular orbits)
• Smaller the orbit ? lower the energy, vice
  versa
• Excited state electrons move to higher energy
  levels when the atom gains energy
• Photon emitted when electrons falls back to
  ground state

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Quantum Mechanical Model

• Bohr model determined incorrect
• Only worked for hydrogen
• Did not account for chemical behavior
• Louis deBroglie proposed electron wave-particle
  duality
• All moving particles exhibit wave-like
  characteristics
• Heisenberg Uncertainty Principle it is
  impossible to know both the velocity and position
  of a particle at the same time (He balloon)

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Quantum Model

• Erwin Shrödinger Austrian physicist using
  complex equation, developed quantum mechanical
  model (electron cloud) of the atom
• Electrons treated as waves
• Electrons not in circular orbits
• Mathematically predicts probable location of an
  electron

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Quantum numbers

• Every electron designated 4 quantum numbers
• Principal quantum number (n) energy level
• Sublevel (s, p, d, f)
• Orbital 3D region around nucleus that describes
  electrons probable location
• Spin
• Diff. orbitals have diff. shapes

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Orbital Shapes
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Electron configuration

• Arrangement of electrons in an atom
• Aufbau principle each electron occupies the
  lowest energy orbital available
• All orbitals w/i an energy level are of equal
  energy (ie 2px 2py 2pz, etc.)
• All sublevels w/i an energy level have diff.
  energies (ie 2p gt 2s, etc.)
• Sublevels increase in energy according to s lt p lt
  d lt f.
• Orbitals of one sublevel may overlap those in
  another energy level.

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Orbital filling
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Electrons Filling
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Write electron configurations for the first 10
elements.
Element Electron Configuration Orbital Notation Electron Dot Diagram
Hydrogen 1S1
Helium 1S2
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen 1S2 2S2 2P4
Fluorine
Neon

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Orbital Notation

• Pauli exclusion principle only two electrons
  with opposite spins can occupy an orbital
• Hunds rule single electrons with the same spin
  must occupy each equal energy orbital before
  electrons can be paired

• How to
• Draw line for each orbital
• s 1
• p 3
• d 5
• f 7
• Draw arrow for each electron
• Follow Paulis Hunds rules

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What element is it?
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Electron Dot Formulas

• Valence electron electron in an atoms highest
  energy level
• Identified by an elements group number
• No element has more than eight
• Transition metals have either 1 or 2

Group valence e-
1
2
13
14
15
16
17
18
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Electron Dot Formulas

• Draw one dot for each valence electron
• 1 5
• 8 2
• 4 6
• 7 3