Principles of Chemistry

1
Principles of Chemistry
MODERN ATOMIC THEORY
CHAPTER 11
2
Modern Atomic Theory

• Develop a more detailed view of the atomic
  structure
• electron arrangements
• Build on our understanding of periodic groups
• chemistry
• periodic organization

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3
Rutherfords Model

• Devised the nuclear atom
• Bombarded metal foil with alpha particles
• expected bombardment to completely pass through
  the foil
• Observed deflection in all directions
• Nucleus consists of a positive core
• Nucleus is small relative to the size of an atom

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4
Review Rutherfords Experiment
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5
Unanswered Questions

• What are the electrons doing?
• Do they move?
• Are they grouped together?
• Why arent the negative electrons attracted to
  the nucleus causing it to collapse?

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6
Electromagnetic Radiation

• When you feel warm when you hold your hand near
• A light bulb
• Embers of wood
• Sunlight
• Electromagnetic radiation - energy is being
  transmitted from one place to another by light

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7
Electromagnetic Radiation

• Wavelength - symbolized by lambda (?) is the
  distance between two consecutive wave peaks or
  two consecutive points on a wave that are on the
  same X axis

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Electromagnetic Radiation

• Frequency (f v/?) - a measure of how many wave
  peaks pass a certain point per given period

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Electromagnetic Radiation

• Electromagnetic radiation - energy being
  transmitted from one place to another by light
• We visualize ER as a wave that carries energy
  through space
• Think of a beam of light as a stream of tiny
  packets of energy called photons

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10
Emission of Energy By Atoms

• Atoms and light - When atoms are heated from a
  flame atoms absorb energy
• Excited - atoms are said to become excited
• Light - some of the excess energy is released as
  photons of light
• Energy States- as atoms release a photon of light
  they move to a lower energy state
• Atoms have different energy states
• These states correspond to photons of specific
  colors

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11
Emission of Energy By Atoms
Excited State
Energy
energy added (flame)
Ground State
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Emission of Energy By Atoms
Excited State
photon of red light emitted (energy released)
Energy
Ground State
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Emission of Energy By Atoms

• Atoms have different energy states
• Energy states correspond to photons of different
  energies
• Lithium - red light, energy change corresponds to
  photons of red light
• Copper - green light
• Sodium - yellow light

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14
Energy Levels of Hydrogen

• Energy contained in the photon corresponds to the
  change in energy that the atom experiences
• Each photon of blue light energy gt red light
  energy
• Color of light - corresponds to wavelength
• When we study the photons emitted
• See only certain colors
• discrete energy levels
• never emit levels between these levels

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15
Energy Levels of Hydrogen
Quantized - only certain values are allowed
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16
Continuous vs Discrete
Energy
Discrete(quantized)
continuous
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17
Bohr Model of the Atom

• Model of an atom with quantized energy levels
• Agreed with the hydrogen emission results
• Electrons orbit the Nucleus
• Electron orbitals correspond to energy levels
• These levels are quantized (discrete)
• Electrons can jump to different orbits by
  absorbing or emitting a photon of light
• These photons are discrete
• Why we see specific colors for specific atoms

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18
Bohr Model of the Atom

• Bohr Model works for Hydrogen
• It doesnt work for other atoms
• Too simple but it paved the way for later
  theories
• Electrons do not move around the nucleus in
  circular orbits like planets orbiting the sun
• We dont know exactly how electrons move in an
  atom

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19
Wave Mechanical Model

• Bohr model assumed the electron moved in circular
  orbits
• Wave Model electrons states are described by
  orbitals
• Orbitals are nothing like orbits
• Think of Orbitals as an area of space where
  electrons travel in a semirandom distribution
• Image below The more intense color of the dot,
  the more likely it is that the electron will be
  found at that point

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20
Wave Mechanical Model

• Wave Mechanical Model shortfalls
• Gives no information as to when the electron
  occupies a certain point
• How it moves
• Some think we can never know the details of
  motion
• There is confidence that the electron does not
  orbit as Bohr modeled

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21
The Orbitals

• Orbitals are organized in shapes
• s, p, d and f
• Each orbital shape holds electrons
• discrete electron number each
• s up to 2 electrons
• p up to 6 electrons
• d up to 10 electrons

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22
The s Orbitals
The size of the orbital is defined by an area
which contains 90 of the total electron
probability
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The pz Orbitals
The size of the orbital is defined by an area
which contains 90 of the total electron
probability
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The py Orbitals
The size of the orbital is defined by an area
which contains 90 of the total electron
probability
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25
The px Orbitals
The size of the orbital is defined by an area
which contains 90 of the total electron
probability
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26
Electrons can Absorb Energy

• Bohr model
• electrons absorb energy
• electrons would jump to an orbital of a greater
  radius
• Wave Mechanical Model
• electrons also absorb energy
• electrons jump to different kinds of orbitals s,
  p, d and f

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27
The Orbitals

• Principal energy levels
• discrete energy levels
• sub-levels containing either
• s
• s, p
• s, p and d
• s, p, d and f
• no more than one s, p, d and f orbital in each
  principal energy level

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28
Principal Energy Levels

• Relative size of spherical 1s, 2s and 3s orbitals

1s
2s
3s
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Wave Mechanical Model

• spin - each electron appears to be spinning as a
  top spins on an axis
• we represent spin by an up or down arrow
• arrows indicate that the electron is spinning in
  one direction or the other
• Pauli exclusion principal - an atomic orbital can
  hold a maximum of two electrons and those two
  electrons must have opposite spins

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30
Putting it all together
1s
s is the sub-level
1 is the principal energy level
Two electrons fit in the 1s orbital and spin in
opposite direction
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31
Applying what we know
1s
11
22.989770
2s
2p
Na
3d
3s
3p
4d
4s
4p
4f
Sodium
5d
5s
5p
5f
Determine the electron configuration (electron
arrangement) of sodium
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Applying what we know
Fill the electrons using this chart
1s
11
22.989770
2s
2p
Na
3d
3s
3p
4d
4s
4p
4f
Sodium
5d
5s
5p
5f
electrons
2

2
1s2
configuration
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33
Applying what we know
1s
11
22.989770
2s
2p
Na
3d
3s
3p
4d
4s
4p
4f
Sodium
5d
5s
5p
5f
electrons
2
2


4
1s2
configuration
2s2
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34
Applying what we know
1s
11
22.989770
2s
2p
Na
3d
3s
3p
4d
4s
4p
4f
Sodium
5d
5s
5p
5f
electrons
2
2
6



10
1s2
configuration
2s2
2s6
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35
Applying what we know
1s
11
22.989770
2s
2p
Na
3d
3s
3p
4d
4s
4p
4f
Sodium
5d
5s
5p
5f
electrons
2
2
6
1




11
1s2
configuration
2s2
2s6
3s1
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36
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2

2
1s2
configuration
2s2
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37
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2
2


4
1s2
configuration
2s2
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38
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2
2
6



10
1s2
configuration
2s2
2p6
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39
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2
2
6
2




12
1s2
configuration
2s2
2p6
3s2
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40
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2
2
6
2




6

18
1s2
configuration
2s2
2p6
3s2
3p6
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41
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2
2
6
2




6
2


20
1s2
configuration
2s2
2p6
3s2
3p6
4s2
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42
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2
2
6
2




6
2


10

30
1s2
configuration
2s2
2p6
3s2
3p6
4s2
3d10
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43
Applying what we know
1s
35
2s
2p
Br
3d
3s
3p
4d
4s
4p
4f
Bromine
5d
5s
5p
5f
electrons
2
2
6
2




6
2


10

5

35
1s2
configuration
2s2
2p6
3s2
3p6
4s2
3d10
4p5
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44
Applying what we know
35
Br
Bromine
1s2
configuration
2s2
2p6
3s2
3p6
4s2
3d10
4p5
reorganize the electron configuration, so that
the greatest principal energy levels are last
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5
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45
Valence electrons
35
Br
Bromine
configuration
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5
Valence electrons are the electrons in the
outermost (highest) principal energy level of an
atom
number of valence electrons
Valence electrons
4s2 4p5
7
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References

• Zumdahl, Steven. DeCoste, Donald. Introductory
  Chemistry A foundation. Sixth Edition. Houghton
  Mifflin Company. ISBN 0-618-80327.
• Wikipedia (some graphics)

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