Electron structure of atoms

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Chapter 6

• Electron structure of atoms

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6.1 Electromagnetic Radiation

• Light that we can see is visible light which is a
  type of electromagnetic radiation.
• Radiant energy is energy that carries energy
  that acts like a wave and travels through space
  at the speed of light.

Earths Radiant Energy
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c speed of light 3.0 x 108 m/s
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Wave characteristics

• Wavelength ?, lambda
• Distance between peaks or troughs in a wave
• Frequency ?, nu
• number of waves, per second that pass a point
  in one second.
• Speed you know this one.

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• Which color has the highest frequency?
• Lowest frequency?
• Largest wave length?
• Smallest wavelength?

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Electromagnetic Spectrum
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Flame testing

• http//www.sciencefriday.com/videos/watch/10227

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Relationship between ? and ?

• Wavelength and frequency are inverses of each
  other.
• ?v c
• ? wavelength in meters (m)
• ? frequency in cycles per second (1/s or s-1 or
  Hertz)
• c speed of light 3.0 x 108 m/s

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Try one!

• The red wavelength emitted from red fireworks is
  around 650 nm and results when strontium salts
  are heated. Calculate the frequency of the red
  light of this wavlength.
• ? v c
• ? (6.50 x 102 nm) 6.50 x 10-7 m
• v 4.61 x1014 s-1 or Hz

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6.2 Plancks Constant

• Max Planck discovered that energy could be gained
  or lost in multiples of a constant (h) times its
  frequency (?).
• h 6.626 x 10-34 J s

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Quantized Energy

• Thus energy is quantized or in steps or packages.
  
• Energy can only be transferred as a whole package
  or quantum.

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Solving equations with Plancks

• ?E change in energy, in J
• h Plancks constant, 6.626 ? 10?34 J s
• ? frequency, in s?1
• ? wavelength, in m

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Calculating energy lost

• The blue color in fireworks is the result of
  heated CuCl at 1200 C. Then the compound emits
  blue light with a wavelength of 450 nm. What is
  the increment of energy (quantum) that is emitted
  at 4.50 x 102 nm by CuCl?

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Answer

• ?E h?
• v 3.0 x 108 m/s 6.66 x 1014 s-1
• 4.50 x 10-7 m
• v c/?
• (6.626 x 10-34 J s) x (6.66 x 1014 s-1)
• 4.41 x10-19J (quantum energy lost in this
  increment)

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photons

• Einstein took Plancks idea a step further and
  proposed that electromagnetic radiation was
  quantized into particles called photons (light).
• The energy of each photon is given by the
  expression
• Ephoton h? hc/?

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Dual Nature of Light

• Light can behave as if it consists of both waves
  and particles.
• Thus light energy has
• mass

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Old-ie but good-ie

• Energy has mass
• E mc2
• E energy
• m mass
• c speed of light

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6.4 The Behavior of the wave De
Broglie

• We can calculate the wavelength of an e-.
• ? wavelength, in m
• h Plancks constant, 6.626 ? 10?34 J s
• v velocity
• m mass in kg

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Question

• Compare the wavelength for an electron (mass
  9.11 x10 -31 kg) traveling at a speed of 1.0
  x107 m/s with that of a ball (mass 0.10 kg)
  traveling at 35 m/s

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Answer

• Electron wavelength 7.27 x 10 -11 m
• ball wavelength 1.9 x 10 -34 m

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? nu frequency v velocityyour
book uses µ for velocity
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Homework

• Chang pg 303 s 1, 2, 7, 9, 15, 20
• BL Pg 230
• 1, 3, 5, 7, 10, 13, 15,19

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The relationship between energy and mass .
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Light Vocabulary

• Diffraction results when light is scattered from
  a regular array of points or lines

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Waves Electrons

• Planck and Einstein proved that electrons in
  atoms act like waves of light
• By understanding waves we can learn about the
  properties of electrons
• The study of the properties of electrons is
  Quantum Mechanics

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Bohr Model

• Proposed the first theory on atom location and
  movement
• His proposal was a little bit right and a lot
  wrongBUT we give him props just the same

Nelis Bohr
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Bohr Model

• Where he was right
• Electrons exist in certain discrete energy
  levels, which are described by quantum numbers
• Energy is involved in moving electrons from one
  energy level to another

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Heisenberg Uncertainty Principle

• Blew the Bohr model out of the water.
• It states that we can only know so much about
  the exact position and momentum of an electron.
• And the electron cloud is born

Werner Heisenberger
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Probability

• Bohr Model
• Probability distribution
• Orbits
• Electron Cloud
• Radial probability distribution
• Orbitals

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6.5 Quantum model of an atom

• Compared the relationship between the electron
  and the nucleus of an atom to that of a standing
  or stationary wave.
• The functions of these waves tell us about the
  electrons location and energy.

Erwin SchrÖdinger
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Schrödinger's Cat

• He proposed a scenario with a cat in a sealed
  box, where the cat's life or death was dependent
  on the state of a subatomic particle. According
  to Schrödinger, the Copenhagen interpretation
  implies that the cat remains both alive and dead
  until the box is opened.

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• We place a living cat into a steel chamber, along
  with a device containing a vial of hydrocyanic
  acid. There is, in the chamber, a very small
  amount of a radioactive substance. If even a
  single atom of the substance decays during the
  test period, a relay mechanism will trip a
  hammer, which will, in turn, break the vial and
  kill the cat. The observer cannot know whether or
  not an atom of the substance has decayed, and
  consequently, cannot know whether the vial has
  been broken, the hydrocyanic acid released, and
  the cat killed. Since we cannot know, the cat is
  both dead and alive according to quantum law, in
  a superposition of states. It is only when we
  break open the box and learn the condition of the
  cat that the superposition is lost, and the cat
  becomes one or the other (dead or alive). This
  situation is sometimes called quantum
  indeterminacy or the observer's paradox the
  observation or measurement itself affects an
  outcome, so that the outcome as such does not
  exist unless the measurement is made. (That is,
  there is no single outcome unless it is
  observed.)

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Quantum numbers!!!!!

• Quantum numbers describe various properties of
  the electrons in an atom.
• There are 4 quantum numbers
• Principal quantum number (n)
• Azimuthual quantum number (angular momentum) (l)
• Magnetic quantum number (ml)
• Electron spin quantum number (ms)

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Principal quantum number (n)

• Integral values 1,2,3,4,5,6,7
• Related to the size and energy of the orbital
• Referred to as the shell or energy level

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Principal quantum number (n)

• As n increases energy increases and orbital size
  increases
• because the electrons are farther away from the
  nucleus and less tightly bound to the positive
  protons.

n1
n4
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Angular momentum quantum number
(l)

• Integral numbers with values from 0 to n-1
• if n 3 possible l values are 0,1,2
• Sometimes referred to as the sub shell number
• Defines the shape of the orbital.

l Orbital shape
0 s
1 p
2 d
3 f
4 g
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Shape of orbitals
l Orbital shape
0 s
1 p
2 d
3 f
4 g
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Magnetic quantum number (ml)

• Integral values from l to -l including zero
• If l 2
• Then ml 2, 1, 0, -1, -2
• Relates to the orientation of the orbital in the
  atom.

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Electron spin quantum number (ms)

• can only have one of two values
• 1/2 or -1/2

½ - ½
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Re cap

• A collection of orbitals with the same n value is
  called an electron shell.
• EX all orbitals that have n 3 are in the third
  shell.
• A collection of orbitals with the same n and l
  values are in the same sub shell
• EX 2s, 2p

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Principle Quantum n of possible l values   Sublevel Shape (l) Orbital number (l) Electron Capacity
1 0 s   S 1 1 x 2 2e
2 0, 1 s p   p 3 3 x 2 6e
3 0, 1, 2 s p d   d 5 5 x 2 10e
4 0, 1, 2, 3 s p d f   f 7 7 x 2 14e
5 0, 1, 2, 3, 4 s p d f g   g 9 9 x 2 18e
6 0, 1, 2, 3, 4, 5 s p d f g h   h 11 11 x 2 22e
7 0, 1, 2, 3, 4, 5, 6 s p d f g h i   i 13 13 x 2 26e
Note In order for the d orbital to be filled the
s and p orbitals must be filled. Table 6.2 page
214
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question

• For the principle quantum level n 5
• Determine the number of allowed sub shells (l)
  and give the number and letter designation of
  each

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Answer

• Recall Angular momentum quantum
• Integral numbers with values from 0 to n-1
• n 5
• l 0 or s, 1 or p, 2 or d, 3 or f, 4 or g

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Nomenclature

• n value l value number of electrons
  in orbital
• 2pY

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Sorting our the numbers

• Orbitals with the same n value are in the same
  shell.
• Ex n 3 is the third shell
• One or more orbitals with the same set of n and l
  values are in the same sub shell
• Ex n 3 l 2 3d sub shell
• n 3 l 1 3p sub shell

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Homework

• Chang pg 305 s 43, 44. 46, 47, 48, 52, 53,56,
  57, 63,
• BLPg 232 41, 43, 45, 46

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Pauli exclusion principle

• In a given atom no electrons can have the same 4
  quantum number
• So when we put more than one electron in an
  orbital we must alternate the spin.
  Thus ms 1/2 -1/2

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• Example of Pauli Exclusion Principal
• Quantum numbers for 2s2
• n l ml
  ms
• 2s 2 0 0
  1/2
• 2s 2 0 0 -1/2

When ever possible electrons will prefer to have
a positive spin. In this case this orbital will
only hold 2 e- so one must be negative
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Question ?
What would the 4 quantum numbers be for 3p3?
Note all electrons have positive spin We will
get to why in a minute
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Answer
n l ml ms 3p 3 1
0 1/2 3p 3 1
1 1/2 3p 3 1 -1
1/2
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Homework

• Page 232-33
• s 52, 53, 54, 56

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Electron configuration

• The order in which electrons are distributed to
  orbitals
• We need to have rules for how we distribute
  electrons. Other wise all the electrons would be
  in the 1s orbital because it has the lowest
  energy
• (e- ? ground state)

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Rule 1Aufbau Principle building up

• Shells fill based on their energy level.
• Lower energy shells fill first followed by high
  energy shells.

START
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H 1s1
Li 1s2 2s1
He 1s2
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p
s
d
f
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How to write EC?
Li 1s 2s
3 electrons
1s2 2s1
Orbital Diagram
electron configuration
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Question ?

• What is the electron configuration for Carbon?

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Answer
C
Carbon has 6 electrons
1s2 2s2 2p2
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Hunds Rule the grocery line rule

• Electrons are distributed among the orbitals or a
  sub shell in a way that gives the maximum number
  of unpaired electrons.

C
1s2 2s2 2p2
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Question

• Write the orbital diagrams and electron
  configurations for the electron configurations of
  each element.
• Nitrogen
• Oxygen
• Fluorine
• Potassium

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Answer
63
A note on vocabulary

• Diamagnetic all electrons are spin paired
• Paramagnetic not all electrons are spin paired

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Question

• Of the following elements which are diamagnetic
  and which are paramagnetic?
• Boron
• Oxygen
• Neon

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Valence Electrons
The electrons in the outermost principle quantum
level of an atom. Ve- to group
Atom Ve- Location Ca
2 4s N
5 2s 2p Br
7 4p3d
Inner electrons are called core electrons.
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Short and Sweet!
Writing the EC for Carbon is one thing but Xenon
(54e-), Argon (18e-)? To write the condensed EC
look to the noble gas BEFORE your element.
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Condensed Form Example

• Cs 55 e-
• Noble gas before it is Xenon Xe 54e-
• Xe
• We still need 1 more e- so we write it in
  
• Xe 6s1

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Xe
Cs
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Question?

• What is the condensed electron configuration for
  Selenium?

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Answer
Se 34 e- Ar 4s2 3d10 4p4
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Ar
Se
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EXCEPTION ALERT!!!

• Memorize the EC of Copper and Chromium. They are
  exceptions to our rules due to stability
• Chromium Ar 4s13d5
• Copper Ar 4s13d10

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EXCEPTION ALERT
After Lanthanum Xe6s25d1 we start filling 4f
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EXCEPTION ALERT
After Actinium Rn7s26d1 we start filling 5f
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Homework

• Pg 233
• s 59, 60, 61,62, 63, 65