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					   Electron Configurations

How does the Bohr Model of
  an atom compare to the
 Quantum Mechanical Model
        of an atom?
  What is the wave nature of light?
• Visible light is part of
  electromagnetic radiation, a
  form of wave energy that
  travels through empty space
  in the form of alternating
  electric and magnetic fields.

• All waves consist of crest
  and troughs traveling away
  from a source at a velocity
  determined by the nature of
  the wave & the material
  through which the wave
  passes.
 How are frequency & wavelength
             related?
• Frequency – rate of wave vibration & is the # of
  waves that pass a given point per second.
     Expressed as Hz – 1 Hz = 1 wave/sec

• Wavelength – determined by frequency &
  velocity, it is the distance between points on a
  continuous wave.
      If frequency ↑ wavelength ↓
      If frequency ↓ wavelength ↑
             Answer Questions
      Wave A                 Wave B




1.   What wave has the shortest wavelength?
2.   Which wave has the longest wavelength?
3.   Which wave has the lowest frequency?
4.   Which wave has the highest frequency?
5.   Which wave do you think has the most
     energy?
             Answer Questions
      Wave A                 Wave B




1.   What wave has the shortest wavelength? A
2.   Which wave has the longest wavelength? B
3.   Which wave has the lowest frequency? B
4.   Which wave has the highest frequency? A
5.   Which wave do you think has the most
     energy? A
6. Which electromagnetic radiation would cause the most damage, gamma-rays
     or radio waves? Why?
    The more light bends the shorter
           the wavelength.
                               R
                               O
                               Y
                               G
                               B
                               I
                               V
•    Which color of light bends the most?
•    Describe its wavelength and frequency.

•    Which color of light has the lowest frequency?
•    Which color has the longest wavelength?
    The more light bends the shorter
           the wavelength.
                                   R
                                   O
                                   Y
                                   G
                                   B
                                   I
                                   V

•    Which color of light bends the most? Purple
•    Describe its wavelength and frequency. Short
     Wavelength High Frequency

•    Which color of light has the lowest frequency? Red
•    Which color has the longest wavelength? Red
                          Niels Bohr
                            (1913)
    Bohr
    • placed p+ & no in the center or nucleus of
      an atom
    • Placed e- in rings around the nucleus
    • worked in Rutherford‟s Lab                Electron




                                        Electron

                      e- gets excited       Proton

Ground state
               e- relax
                    Bohr
• A Quantum model of H based on its
  spectrum.
• Predicted correctly frequencies of the lines
  H atomic emission spectrum.
• Proposed – H atom has certain allowable
  energy states
     Lowest level – ground state
     Gain energy – excited states
• H has many different excited states
   Emission Spectrum of H(sun), H-2
              He, Hg, U
       Visible Spectrum
          ROY G BIV

Hydrogen has 4 colors
         Red
         Aqua
         Blue
        Violet
  (colored lines are
called “spectral lines”
                            Proposed
•   Ground state is the 1st energy level & atom doesn‟t radiate energy

•   Add energy from an outside source e- moves to higher energy level (orbit) to
    excited states

•   An atom emits a photon (color of light) corresponding to the difference
    between energy levels of two orbits.

                                                             Light (has certain
                                                             wavelength &
                                                             frequency = color)

           electron that absorbed                      electron in ground state
           energy and is “excited”                     that emitted light energy

                  ground state


                     nucleus                             nucleus
 Draw the Bohr model of the atom
• The number of protons and neutrons are listed
  in the center of the atom
• The number of electrons must be determined
• The electrons are placed in concentric rings
  around the nucleus
  –   1 The first ring can only hold 2 electrons
  –   2 The next ring can only hold 8 electrons
  –   3 The next ring can only hold 8 electrons
  –   4 The next ring can only hold 18 electrons
  –   5 The next ring can only hold 18 electrons
  –   6 The next ring can only hold 32 electrons
  –   7 The next ring can only hold 32 electrons
            Bohr Model WS
• Fill in the information and place the correct
  amount of e-‟s in each ring

• Fill in the orbitals from the inside (ground
  State) out (excited states)
               Problem
• Failed to explain spectrum of other
  elements.
• Did not fully account for atoms behavior
• Research shows e- do not move in circular
  orbits

•   Did lay groundwork for other models
 What is the quantum mechanical
        model for atoms?

• (1924 – Louis de Broglie 1892-1987)
• Proposed a model to account for fixed
  energy levels of Bohr‟s Model
• Thought that light waves have both wave
  & particle like behavior.
• If waves have particle like behavior could
  particles have wavelike behavior?
           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
   Quantum Mechanical Model
• e- are treated as
  waves
• limits e- to certain
  values
• doesn‟t describe e-
  path
• 3-dimensional
  design
• atomic orbital –
  describes e-
  probable location
                         e- wiggle as the move around nucleus
 Werner Heisenberg (1901- 1976)
Heisenberg Uncertainty Principle
• Impossible to make any measurement on
  an object without disturbing the object,
  even a little.
• States it is fundamentally impossible to
  know precisely both the velocity & position
  of a particle @ the same time.

                        Where is the e-?
 Assign Principle Quantum #‟s (n)
(n) increases as orbitals become larger
• e- away from nucleus have increased
  energy
• n = principle energy level ground state
  (PEL)
•     Ex: n = 1 ground state
           H has a n = 1-6
                PEL contains
• energy sublevels s,p,d,f according to the
  shapes of the atom‟s orbitals.

s - spherical

p - dumbbell shaped

d - f have different shapes
              Energy Levels
• While Bohr‟s model of an atom is an easy
  representation it is not correct. Electrons exist in
  energy levels and must be assigned correctly to
  determine the valence electrons

• There are 4 suborbitals each holding a different
  number of electrons
     s – holds 2 electrons
     p – holds 6 electrons
     d – holds 10 electrons
     f – holds 14 electrons
To determine the electron configuration
for any atom simply look at the periodic
                table

•   Columns = Groups = Family
•   Groups 1 - 2 are s orbitals (He)
•   Groups 13 – 18 are p orbitals
•   Groups 3 – 12 are d orbitals
•   Lanthanide and Actinide are f orbitals
             Periodic Table
• Color your periodic table indicating the s,
  p, d, f elements
• Pp. 161 in book
  s = yellow
  p = purple
  d = blue
  f = green
                   Fill in WS
• Energy levels are numbered from 1 to 7 and are
  where electrons are located. Energy levels can
  only hold a certain # of electrons. Electrons fill
  inner energy levels before they fill outer energy
  levels. Electrons in the outer most energy level
  determine the behavior of an element. Another
  name for these electrons would be valence
  electrons. Atoms with full outer shells are stable
  or inert. Generally, that means 8 electrons and is
  called the octet rule. The exception to this rule is
  He which has only 2 valence electrons.
                Sublevels:

Sublevels are areas within an energy level.
They are designated by the letters s, p, d, f.

s holds 2 electrons             __
p holds 6 electrons          __ __ __
d holds 10 electrons      __ __ __ __ __
f holds 14 electrons __ __ __ __ __ __ __

Each ___ is a ring in the sublevel & holds 2 e-
     Sublevels per Energy Level
•   n = 1 = 1 sublevel    1s
•   n = 2 = 2 sublevels   2s   2p
•   n = 3 = 3 sublevels   3s   3p   3d
•   n = 4 = 4 sublevels   4s   4p   4d     4f

• n = 5-7 are the same as the 4th energy
  level
       Electron Configuration

• A method of keeping track of how many
  electrons are located at each energy level and
  which sublevel they are in. The number
  represents the energy level. The letter
  represents the sublevel. The superscript
  represents how many electrons are located at
  a certain place.
• The period (row number on PT) is important in
  determining the energy level

• To write an electron configuration you must write
  all the electrons in the atom


Energy level→1s2   superscript (number of electrons)




           Sublevel
              Aufbau Diagram
•   1s
•   2s   2p
•   3s   3p   3d
•   4s   4p   4d   4f   Energy pathway for electrons

•   5s   5p   5d   5f
•   6s   6p   6d
•   7s   7p
              Aufbau Diagram
•   1s                  Notice the pathway goes from
                        4s to 3d to 4p. This is b/c the
•   2s   2p             4s electrons have more energy
                        than the 3d, but less energy
•   3s   3p   3d        than the 4p electrons.

•   4s   4p   4d   4f   d suborbitals are in 1 energy
                        level less than the period
•   5s   5p   5d   5f   (row) the element is in.

•   6s   6p   6d        f suborbitals are in 2 energy
                        levels less than the period
•   7s   7p             (row) the element is in.
     Electronic Configurations
• The arrangement of electrons in an atom is
  called the atom‟s configuration.

• Electrons will arrange themselves in a way that
  gives the atom the lowest possible energy.


Energy level→1s2   superscript (number of electrons)




           Sublevel
   3 rules define how electrons are
              arranged…
• The Aufbau principle states that electrons will
  occupy the lowest energy level available

• The Pauli exclusion principle Two e- within same orbit
  must have opposite spins




• Hund‟s rule single e- with the same spin must occupy each
  equal energy orbit before additional e- with opposite spins can
  occupy the same orbital
Practice Electron Configurations
• Fill in arrows to represent electrons

• Follow Aufbau pathway when filling orbitals

• Transfer arrows to other WS and write electron
  configuration notation for each atom
Identify each element
 Identify each element




Fluorine     Phosphorus
         Electron Configuration
               Examples
•   H     1s1
•   He    1s2
•   Li    1s2 2s1
•   Be    1s2 2s2
•   B     1s2 2s2 2p1
•   C     1s2 2s2 2p2
•   N     1s2 2s2 2p3
•   O     1s2 2s2 2p4
•   F     1s2 2s2 2p5
•   Ne    1s2 2s2 2p6
         Electron Configuration
               Examples
•   Na    1s2 2s2 2p63s1
•   Mg    1s2 2s2 2p63s2
•   Al    1s2 2s2 2p63s23p1
•   Si    1s2 2s2 2p63s23p2
•   P     1s2 2s2 2p63s23p3
•   S     1s2 2s2 2p63s23p4
•   Cl    1s2 2s2 2p63s23p5
•   Ar    1s2 2s2 2p63s23p6
•   K     1s2 2s2 2p63s23p64s1
•   Ca    1s2 2s2 2p63s23p64s2
         Electron Configuration
               Examples
•   Sc    1s2 2s2 2p63s23p64s23d1
•   Ti    1s2 2s2 2p63s23p64s23d2
•   V     1s2 2s2 2p63s23p64s23d3
•   Cr    1s2 2s2 2p63s23p64s23d4
•   Mn    1s2 2s2 2p63s23p64s23d5
•   Fe    1s2 2s2 2p63s23p64s23d6
•   Co    1s2 2s2 2p63s23p64s23d7
•   Ni    1s2 2s2 2p63s23p64s23d8
•   Cu    1s2 2s2 2p63s23p64s23d9
•   Zn    1s2 2s2 2p63s23p64s23d10
       Electron Configuration
             Examples
• Cs        1s2 2s2 2p63s23p64s23d104p6
            5s24d105p66s1

• Hg        1s2 2s2 2p63s23p64s23d104p6
            5s24d105p66s24f145d10
 Noble Gas (Short Hand) Notation
    of Electron Configurations
1. Find the noble gas in the row above the
   element you need to write the notation
   for and put in brackets [ __ ].

    Ex: Looking for S (sulfur) the noble
        gas would be Neon

                   S[Ne]
 Noble Gas (Short Hand) Notation
    of Electron Configurations
2. Write the notation starting in the period
  (row) the element is in.

                 S[Ne]3s23p4

Write noble gas notation using these
elements:
               Br, Ag, U, Xe
  What are Valence Electrons?
• e-„s that determine chemical properties of
  an element

• These e- are in the outermost orbitals
  usually the highest principle energy level
 How are valence e- determined
• Find which group
  (column) element is
  in and that is how    1   2   13 14 15 16 17 18
  many valence
  electrons the         1   2   3   4   5   6   7   8
  element has.

• Works for groups
  1-2 (He has only 2
  ve-) 13-18
   How are valence e- determined
    from electron configurations


S[Ne] 3s2 3p4 (6 e- in outermost level)

Cs[Xe] 6s1 (1 e- in outermost level)
    What are Electron Dot or Lewis
             Structures?
            (1875-1946)
• Li[He] 1s1       Li    1 ve-

• Ne[He] 2s2 2p6   Ne    8 ve-
    What are Electron Dot or Lewis
             Structures?
            (1875-1946)
• Li[He] 1s1       Li    1 ve-


• Ne[He] 2s2 2p6   Ne    8 ve-

				
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posted:11/24/2011
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