Chapter 13 Electrons in Atoms

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Chapter 13 Electrons in Atoms

• C. Smith

2
I. Models of the AtomA. The Evolution of
Atomic Models

• 1. There are four major models of the atom that
  have been developed from John Dalton theory.
• 2. Dalton Atomic Theory a. He theorized that
  an atom was indivisible, uniformly dense
  sphere. b. He theorized that all atoms of the
  same element have the same mass and the same
  chemical behaviors. c. He theorized that atoms
  of different elements have different chemical
  behaviors. d. He theorized that atoms of
  different elements combine to form compounds.
  (Example H2O)

3
I. Models of the AtomA. The Evolution of
Atomic Models

• 3. J.J. Thomson realized that the accepted model
  did not take electrons into account. a. He is
  credited with the discovery of the negatively
  charged particles called electrons. b. He
  theorized that the atom is a dense sphere with a
  positive charge and also contains negative
  charged particles. c. His model is also known
  as the Plum Pudding model.

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I. Models of the AtomA. The Evolution of
Atomic Models

• 4. Ernest Rutherford expanded on Thomsons
  theory. a. The atom has a very dense center of
  positive charge called the nucleus. b. The
  nucleus contains the protons for the atom and
  make up more than 99.9 of its mass. c. The
  electrons surround the nucleus.

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I. Models of the AtomA. The Evolution of
Atomic Models

• 5. Niels Bohr proposed a model in which the
  electrons move around the nucleus. a. He
  theorized that the electron orbits the
  nucleus. b. He theorized that the orbits were
  different energy levels that the electrons travel
  in and can be excited to a high energy level. c.
  He theorized that the electrons did not lose
  energy and fall into the nucleus. (The weakness
  in Rutherfords theory.)

6
I. Models of the AtomA. The Evolution of
Atomic Models

• 6. A quantum of energy is the amount of energy
  required to move an electron from its present
  energy level to the next higher one. (Also called
  a quantum leap)

7
I. Models of the AtomB. The Quantum Mechanical
Model

• 1. Erwin Schrödinger related the amplitude of
  the electron wave, Y (psi), to any point in
  space around the nucleus. 2. His equation
  treated the electron as a wave and developed an
  equation to describe this behavior.

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I. Models of the AtomB. The Quantum Mechanical
Model

• 3. The quantum mechanical model comes from the
  mathematical solutions to Schrödinger
  equation.4. The quantum mechanical model does
  not define an exact path for the electron to take
  around the nucleus but instead estimates a
  probability of finding the electron in a certain
  position.5. Since the volume occupied by an
  electron is somewhat vague, it is better to
  refer to an electron cloud.

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I. Models of the AtomB. The Quantum Mechanical
Model
10
I. Models of the AtomC. Atomic Orbitals

• 1. Electrons can occupy only specific energy
  levels.2. These energy levels, referred to as
  n is called the principal quantum number.3.
  The maximum number of electrons that a level can
  contain is 2n2 (Whole number integers only).

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I. Models of the AtomC. Atomic Orbitals

• 4. These are referred to as sublevels and the
  number of sublevels for each energy level is
  equal to the value of the principal quantum
  number.5. The lowest energy level is s.6.
  The second lowest is p ,the third lowest level
  is d, and the remain level is f.

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I. Models of the AtomC. Atomic Orbitals

• 7. The s orbital is spherical in shape and
  contains 2 electrons and is also called the
  ground state. 8. The p level is barbell shape
  and exist along the axis of the plane.9. The
  d orbitals exist in the plane. 10. The s
  level contains 1 pair of electrons, p contains
  3 pairs, d contains 5 pairs, and f contains
  7 pairs.

13
II. Electron Arrangement in AtomsA. Electron
Configurations

• 1. The ways in which electrons are arranged
  around the nucleus is called electron
  configuration.2. The are three rule that tell
  you how to find the configurations. a. Aufbau
  principle
• b. Pauli Exclusion principle
• c. Hunds Rule

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II. Electron Arrangement in AtomsA. Electron
Configurations

• 2a This is called the Aufbau principle. 1.
  Electrons enter at the lowest energy level. 2.
  Some energy levels overlap into the adjacent
  principal energy level.

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II. Electron Arrangement in AtomsA. Electron
Configurations
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II. Electron Arrangement in AtomsA. Electron
Configurations

• 2b. This is called the Pauli exclusion
  principle. 1. Spectral data shows that only 2
  electrons can exist in the same orbital. 2.
  Electrons behave as if they were spinning about
  their own axis. 3. When electrons occupy the
  same orbital they are said to spin in opposite
  directions (assign 1/2 and 1/2).

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II. Electron Arrangement in AtomsA. Electron
Configurations

• 2c. This is called Hunds Rule. 1. Also with
  the principle, you must have all orbital filled
  with one electron before you can add the other
  electron with opposite spin to the orbital. 2 .
  All elements would like to have a completely
  filled orbital and the maximum number of
  electrons that can exist in a filled orbital is
  eight.

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II. Electron Arrangement in AtomsA. Electron
Configurations

• 3. When writing electron configurations, you
  must know the total number of electrons for the
  element (atomic number).4. Write down the
  sequence of orbitals.5. Draw circle to
  represent the orbitals.6. Place arrows (or
  slashes) to represent the electrons.

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II. Electron Arrangement in AtomsA. Electron
Configurations
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II. Electron Arrangement in AtomsA. Electron
Configurations
21
II. Electron Arrangement in Atoms B. Exceptional
Electron Configurations

• 1. Filled sublevels are more stable than partial
  filled or half-filled sublevels. 2. But
  sometimes half-filled may be more stable than
  other configurations.

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III. Physic and the Quantum Mechanical ModelA.
Light and Atomic Spectra

• 1. This energy consist of variation in electric
  and magnetic fields taking place in a regular,
  repeating fashion. (Electromagnetic energy)2.
  Light is a form of electromagnetic radiation

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III. Physic and the Quantum Mechanical ModelA.
Light and Atomic Spectra

• 3. If you plot the strength of the variation
  against time, the graph shows waves of
  energy.4. The number of waves peaks that occur
  in a unit of time is called the frequency of the
  wave (Greek letter v and units are Hertz (Hz)).

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III. Physic and the Quantum Mechanical ModelA.
Light and Atomic Spectra

• 5. The distance between the peaks is the
  wavelength (Greek letter ?) and the amplitude of
  a wave is the height from the maximum
  displacement from zero.6. These characteristics
  of waves are related by the statement c ?v
  where c is the speed of light which is 3.0 x 10
  8 m/s.

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III. Physic and the Quantum Mechanical ModelA.
Light and Atomic Spectra

• 7. The wavelengths of light can separate into a
  spectrum of colors.8. This is part of the
  visible spectrum.9. There are two types of
  spectrums. a. Adsorption spectrum. b.
  Emission spectrum.

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III. Physic and the Quantum Mechanical ModelA.
Light and Atomic Spectra

• 10. Adsorption spectrum is when the energy
  gained by the excited electron is is absorbed so
  that it is missing in visible spectrum.11.
  Emission spectrum is when the excited electrons
  lose the energy and it is emitted at specific
  points on the visible spectrum that appear as
  single lines on a detector.

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III. Physic and the Quantum Mechanical ModelB.
The Quantum Concept and the Photoelectric Effect

• 1. Max Planck used Bohrs theory to develop his
  hypothesis.2. He assumed that energy is given
  off in packets called quanta or photons instead
  of a steady stream.

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III. Physic and the Quantum Mechanical ModelB.
The Quantum Concept and the Photoelectric Effect

• 3. He stated that the amount of energy given
  off is related to the frequency of light (v -
  Greek letter nu).4. He thought a quantum energy
  was equal to E hv where h is the constant 6.63
  x 10 -34 J/Hz (Hz Hertz).

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III. Physic and the Quantum Mechanical ModelB.
The Quantum Concept and the Photoelectric Effect

• 5. Albert Einstein proposed that light could be
  described as a quanta of energy that behaved as
  if they were particles. 6. The dual
  wave-particle behavior is called the
  photoelectric effect.

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III. Physic and the Quantum Mechanical ModelB.
The Quantum Concept and the Photoelectric Effect

• 7. In the photoelectric effect, metals eject
  electrons when light shines on them.8. The
  frequency and the wavelength of the light
  determine if the photoelectric effect will occur.

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III. Physic and the Quantum Mechanical ModelC.
An Explanation of Atomic Spectra

• 1. Consider the electron of a hydrogen atom in
  its lowest energy level, or ground state.2. The
  quantum numbers represent the different energy
  states.

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III. Physic and the Quantum Mechanical ModelC.
An Explanation of Atomic Spectra

• 3. The difference between these energy states
  corresponds to the lines in the hydrogen
  spectrum.4. With more complex atoms more than
  one electron is present and the interaction
  between electrons make solution to the equation
  impossible because electrons have the same charge.

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III. Physic and the Quantum Mechanical ModelC.
An Explanation of Atomic Spectra

• 5. It is possible to approximate the electronic
  structure of a multi-electron atom.6. This
  approximation is made by first calculating the
  various energy states and quantum numbers.7.
  It is assumed that the various electrons in
  multi-electron atom occupy the same energy states
  without affecting each other.

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III. Physic and the Quantum Mechanical ModelD.
Quantum Mechanic

• 1. Louis De Broglie proposed an idea based on
  Plancks theory and Einsteins relationship of
  matter and energy.2. Using the two formulas, he
  equated mc2 h? (v frequency).

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III. Physic and the Quantum Mechanical ModelD.
Quantum Mechanic

• 3. He substituted v for the velocity of light
  (c) so that mv 2 hv and v /? for v to get
  mv 2 hv /?. (? - Lamda wavelength)4. To
  determine wavelength (?), the equation becomes ?
  h/mv .

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III. Physic and the Quantum Mechanical ModelD.
Quantum Mechanic

• 5. This allows for predictions of the
  wavelength of a particles.6. Werner Heisenburg
  refined ideas about atomic structure.7. He
  stated that it is impossible to know the exact
  position and momentum of an electron in an atom.

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III. Physic and the Quantum Mechanical ModelD.
Quantum Mechanic

• 8. Using the equation for momentum, he proposed
  that mv p where m is mass and p is momentum.
  9. The uncertainty of position and momentum are
  related to Plancks constant ?p ?x gt h where p
  is momentum and x is position (? change).10.
  Because h is constant, ? p and ? x are inversely
  proportional to each other.