Electrons in Atoms

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Electrons in Atoms

• Chapter 5

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Duality of Light

• Einstein proved that matter and energy are
  related E mc2
• The smaller matter becomes the more like energy
  it behaves.
• We know electrons are very small therefore behave
  like energy.

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Duality of Light

• During the 1800s, Chemists and physicists found
  light emitted properties of a wave.
• In 1905, Albert Einstein explained the
  photoelectric effect using a particle theory of
  light.
• Scientist have accepted a dual theory of light,
  either wave or particle.

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Wave Nature of Light

• Electromagnetic Radiation Form of energy that
  exhibits wavelike behavior as it travels through
  space.
• Visible light is a form of electromagnetic
  radiation.
• All electromagnetic radiation travels at 3.00 x
  108 m/s

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Wave Nature of Light
Crest
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Wave Nature of Light

• Wavelength represented by ?, is the shortest
  distance between equivalent points. Unit for
  wavelength is meter.
• Frequency represented by ? Greek letter nu, is
  the number of waves that pass a given point per
  second. Unit for frequency is s-1 or 1/s

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Wave Nature of Light
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Wave Nature of Light

• Since all electromagnetic radiation travels at
  3.00 x 108 m/s, there is a distinct relationship
  between frequency and wavelength.
• c ? ?
• c is a constant, 3.00 x 108 m/s, the speed of
  light
• ? is the wavelength of light in meters
• ? is the frequency in s-1 or 1/s or Hz which
  s-1 or 1/s

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Wave Nature of Light

• Microwaves are used to transmit information.
  What is the wavelength having a frequency of 3.44
  x 109 Hz
• We know c ? ?
• We know c 3.00 x 108 m/s and we know ? 3.44 x
  109 Hz
• Solve for ?
• ? c/ ?
• ? 3.00 x 108 m/s/ 3.44 x 109 Hz
• ? .0872m or 8.72 x 10-2 m

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Wave Nature of Light

• An X ray has a wavelength of 1.15 x 10-10 m.
  What is the frequency?
• 2.61 s-1
• Yellow light has a frequency of 5.09 x 1014 s-1.
  What is the frequency?
• 5.89 x 10-7 m.

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Particle Nature of Light

• Max Plank did experiments studying a black box
  and the heat given off by it.
• Plank determined energy can only be released or
  absorbed by atoms in small specific amounts
  called quanta.
• He suggested light consisted of photons.

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Particle Nature of Light

• Plank proposed the energy of a single quantum is
• E h ?
• E is the energy of a quantum.
• h is Plancks constant, 6.626 x 10-34 J x s, J is
  the symbol of a joule, which is the SI unit of
  energy.
• ? is frequency.

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Particle Nature of Light

• Calculate the energy of a photon with a frequency
  of 7.23 x 1014 s-1 .
• We know E h ?
• We know h 6.626 x 10-34 J x s
• We know v 7.23 x 1014 s-1
• E 6.626 x 10-34 J x s x 7.23 x 1014 s-1
• E 4.79 x 10-19 J

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Particle Nature of Light

• Calculate the energy of a photon with the
  frequency of 6.32 x 1020 s-1.
• 4.19x 10-13 J
• Calculate the energy of a photon with a
  wavelength of 5.98 x 10-7 m.
• 3.32 x 10-19 J

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Relationships of Photons

• v?, E?, ??
• v?, E?. ??

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Atomic Emission Spectra

• Neon lights
• Atoms absorb energy and emit light to release
  energy
• Atomic emission spectrum set of frequencies of
  the electromagnetic waves emitted by atoms of the
  element.
• Unique for all different elements.

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Electrons as Waves

• de Broglie proposed electrons have wave like
  nature and the wavelength of the electron can be
  calculated
• ? h/mv
• h Plancks constant
• m mass
• v velocity

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Bohr Model of the Atom

• Bohr built upon Plancks and Einsteins concepts
  of quantized energy.
• The chemical properties of the element are
  determined by the number of electrons in the
  outer orbits.
• Used spectra from hydrogen atom
• Proposed that hydrogen atom has only certain
  allowable energy states
• Ground State Lowest allowable energy state
• Stated electron moves in only certain circular
  orbits.

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Bohr Model of the Atom

• The smaller the electrons orbit, the lower the
  atoms energy state. Larger orbit, higher energy
  state.
• First orbit closest to the nucleus, n1, second,
  n2

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Bohr Model of the Atom

• When energy is added to an atom, the electron
  moves from the ground state, n1, to a higher
  energy orbit, excited state, n2
• When an electron is in an excited state, it can
  drop from the higher energy orbit to a lower
  energy orbit.
• The atom emits a photon corresponding to the
  difference between the corresponding energy
  levels.

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Bohr Model of the Atom

• 1. proposed that while circling the nucleus of
  the atom, electrons could only occupy certain
  discrete orbits, that is to say energy levels
• 2. electrons give or take energy only when they
  change their energy levels. If they move up, they
  take energy if they move down, they release
  energy.  This energy itself is released in
  discrete packets called photons
• 3. an electron which is not in its native energy
  level always has to fall back to its original,
  stable level.

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Bohr Model of the Atom

• Bohr model perfectly explained the hydrogen atom
• but, failed to explain any of the other atoms.
• Therefore, the Bohr model of the atom is not the
  currently accepted model of the atom.

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Heisenberg Uncertainty Principle

• It is impossible to measure an object without
  disturbing the object.
• Heisenberg attempted to determine exact location
  of electrons using photons.
• He found since photons and electrons have
  relatively the same amount of kinetic energy, the
  photon would disturb the position and velocity of
  the electron.

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Heisenberg Uncertainty Principle

• It is impossible to know precisely both the
  velocity and position of a particle at the same
  time

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Quantum Mechanical Model of Atom

• Schrödinger created an equation to accurately
  determine where an electron is.
• Unlike Bohr model, makes no attempt to determine
  orbit of electron.
• States electrons are in noncircular orbitals.
• Orbitals are based on probability of location of
  electron.

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Atomic Orbitals

• Principal quantum numbers (n) indicate the
  relative sizes and energies of atomic orbitals.
• As n increases, the orbital is further away from
  the nucleus and has more energy.
• n has whole number values of 1, 2, 3, etc.

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Atomic Orbitals

• Principle energy levels contain energy sublevels.
• Sublevels are signified by letters s, p, d, or f.
• The letter determines the shape of the sublevel.

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S orbital

• First found at energy level 1
• Holds 2 electrons
• Spherical
• 1s, 2s, 3s,

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P Orbital

• First found at energy level 2
• 3 different shapes per energy level
• 2 electrons per shape
• dumb-bell shaped

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D Orbitals

• First found at energy level 3.
• 5 different shapes
• 2 electrons per shape
• Complex shapes

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F Orbitals

• First found at energy level 4
• 7 different shapes
• 2 electrons per shape
• Very complex

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f Orbital
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First Four Principal Energy Levels
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Quantum Numbers

• Principle quantum number n
• 2nd or Azinmuthal quantum number describes
  shape 0, 1, 2, 3 (s, p, d, f)
• Magnetic quantum number ml orientation in
  space, whole numbers -1, 0, 1
• Spin s, either ½ or ½, one e- ½ other e- has
  ½.

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