Chemistry Unit 8 by yurtgc548

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									      Chemistry Unit 8

Part I - Quantum Theory and Bonding
         with valence electrons
          Chemistry Parts I and II!
• We Learned: How atoms, molecules, and reactions
  behave according to the two main laws of the
  universe:
  – Law of Constant Composition
  – Law of Conservation of Matter
• You Will Learn:
  – What is the latest theory that describes the atom?
  – How do reactions occur?
  – Why do some reactions occur but others don’t?
• Electron arrangement around atom accounts for just
  about everything!
     Theories of the Atom: Oh where, oh
        where are the electrons????
• Dalton: Atoms are solid
  spheres
• J.J. Thompson: Discovered
  first subatomic particle:
  electron
• Electrons were first thought
  to be arranged in a random
  blob
• Hypothesized that the atom
  was like “sprinkles on ice
  cream”
    Theories of the Atom: The Birth
             of the Nucleus
                             • Rutherford’s
• Rutherford: Discovered       experiment
  first subatomic particle
  – Proton (+)
  – Condensed in center
  – Called it the nucleus
      Theories of the Atom: Something
               wasn’t right…
• Problem with
  Thompson’s and
  Rutherford’s Theory:
• Atoms were observed to
  give off red through
  violet light when excited
  – Radiation
  – Heat
     Super Basic Reason Why Atoms
             Emit Light…
• Atom at “ground state” = stable
• Atom absorbs energy, enters an excited state = unstable
• To re-stabilize, the atom releases any absorbed energy as
  light
• Depending on how much energy it releases, it will give of
  different frequencies of light
   – High amounts of energy released = violet light
   – Low amounts of energy released = red light
• Different atoms gave off different combinations of light
 What does this imply about the
 arrangement of electrons in an
            atom?
           Flame Test Link

 Why does this create a problem
for Thompson’s and Rutherford’s
            theory?
    Bohr’s Theory: Almost There…

• Electrons orbit around
  nucleus in energy levels
• Set number of electrons
  in a level
• Fixed orbit path
• Light comes from when
  “excited” electron falls
  back down to its old
  energy level
   Yet Again… Hydrogen Messes It
             All Up!
• Bohr’s theory was able
  to explain everything
  except hydrogen
• Why would hydrogen
  give off up to 4
  frequencies of
  light????
       Shrodinger Saves The Day!
• Problem with Bohr’s Theory:
• electron does not inhabit a fixed
  orbit like planets around the sun
• electron can have a range of
  motion within a certain distance
  from the nucleus of the atom
• Quantum (wave mechanical)
  model explains this range of
  motion
          Shrodinger’s Quantum Theory
• Electrons act as both a particle and a wave - like light
   – http://www.youtube.com/watch?v=ZtXGq2I4ZI8
• Bohr model – electrons were particle only and moved in circular
  orbits
• Quantum model – and electron movement and energy is described by
  orbitals
• Looks like: fire fly movement around a spot with food – what would
  the light path look like?
• Orbital – general area at any point in time and electron could be
  found at a certain distance from the nucleus and state of energy
   – Electrons are caged at an energy level instead of on a leash
• The path of an electron is not definite; you just predict the
  probabilities of finding an electron at that point in a given instant
• Why do we care? Helps us understand and predict bonding; harness
  the power of the atom to make whatever we want
Quantum Model Of Hydrogen
      Shrodinger’s Quantum Theory
• Equation - answers describe path of electron
• Gives 4 answers:
  –   Size and energy (n)
  –   Shape (L)
  –   Direction (ML)
  –   Spin (Ms)
• Each electron in atom has these 4 numbers to
  describe its location and path
     Principle Quantum Number (n)
• Size and energy of an orbital
• Greater value of n, greater distance from the
  nucleus
• Whole numbers from 1 - 7
• All orbitals with the same n number are referred
  to as a shell
• N = period of periodic table
    N=…
1
2
3
4
5
6
7


6
7
Angular Momentum Quantum Number
               (L)
• Shape of orbital
• Depends on the number
  that each L takes on
• Referred to as a letter
• Sublevels of the main
  energy levels (n)
  – 0 = S – sphere
  – 1 = P – two lobes (peanut)
  – 2 = D – four lobes (double
    peanut)
  – 3 = F – 8 lobes (flower)
“S” Block

                        “P” Block



            “D” Block




                    “F” Block
    Allowed values for L are 0 to n-1
     “S” Block
                                “P” Block
1
                 “D” Block is
2                   off by 1!
3                  (starts at
                  n=3 not 4)
4
5
6
7
                          “F” Block

6
7
• As “n” increases, the size
  of the shape increases,
  but the shape stays the      3s
  same
• Orbitals are written by
  pairing the “n” and “s”
  together                      2s


                                    1s
     Magnetic Quantum Number (ML)
• Magnetic Charge has a direction (North or South)
• Orbitals face certain directions in 3D space
   – X (east - west or left - right)
   – Y (North - South or forward - backward)
   – Z (Up - Down)
• ML tells you what area an electron will likely travel
• Paths are represented by numbers
   – Allowed values are – L … 0 … +L
• The number of digits tells you the number of areas
• Each “area” can accommodate 2 electrons
   – Every 2 elements on p-table = 1 ML
             Every 2 elements on p-table = 1 ML
“S” Block

                        “P” Block



            “D” Block




                    “F” Block
                 ML For an “S” Orbital
• “L” for an s orbital is…
   – 0
• ML = -L … 0 … +L
• Allowed “paths” for ML are:
   – 0…0…+ 0
   – Or just 0
• An electron in an s-orbital can
  only have 1 possible travel
  area in 3D space
• Capacity: 2 electrons
                  ML For a “P” Orbital
• “L” for an p orbital is…
                                 Py      Pz
   – 1
• ML = -L … 0 … +L
• Allowed “paths” for ML
  are:
   – 1…0…+ 1                     Px
   – 3 digits = 3 directions
• An electron in a p-
  orbital can inhabit 3
  areas in 3D space
• Capacity: 6 electrons
                 ML For a “D” Orbital
• “L” for an D orbital is…
   – 2
• ML = -L … 0 … +L
• Allowed “paths” for ML
  are:
   – 2…-1…0…+ 1…+2
   – 5 digits = 5 directions
• An electron in a d-
  orbital can inhabit 5
  areas in 3D space
• Capacity: 10 electrons
              ML For an “F” Orbital
                                 – 7 digits = 7 directions
• “L” for an F orbital is…
   – 3
                              • An electron in an f-
                                orbital can inhabit 7
• ML = -L … 0 … +L              areas in 3D space
• Allowed “paths” for ML are: • Capacity: 14 electrons
   – 3…-2…-1…0…+1…+2…+3
         Spin Quantum Number (Ms)
• Each “Area” or ML can
  hold 2 electrons at a time
• The spin of an electron is
  clockwise or counter
  clockwise
• Ms = +0.5, -0.5
• Or
• Summary!
            Electronic Configuration
• Maps electrons               • Examples:
• Use: predicting
  bonding/ionization
                                 – He: 1s22s2
• Displays 2 quantum             – Ne: 1s22s22p6
  numbers:
   – N
   – L
• Lumps all ML together
• Total electrons in all ML
• Once L is full, move on to
  next orbital
  Steps to find electronic configuration
• Numbers of energy levels goes by the period (row)
  # with exception of D-block; it starts at n=3
• The s, p, d, f block tells you which orbital are being
  filled (L)
• To fill in the number of electrons in each orbital for
  an element:
  – Count along the blocks of the periodic table starting
    from H
• Continue until you reach the element you are
  looking for
     Try: Ne, Si, As, V (start at H!)
    “S” Block
                                     “P” Block
1               “D” Block is off
                by 1! (starts at
2                 n=3 not 4)

3
4
5
6
7
                                   “F” Block

6
7
  What if you had to configure Radon
               (86)???
• Noble gas shortcut
• Instead of starting from H, start from last noble gas
  behind your element
• [noble gas] remaining configuration
• Example - Rn: [Xe] 7s26d107p6
    Try: Cl, Bi, Ag (start at a noble gas!)
      “S” Block
                                       “P” Block
1                 “D” Block is off
                  by 1! (starts at
2                   n=3 not 4)

3
4
5
6
7
                                     “F” Block

6
7
                     Types of Electrons
• Core and Valence                              Ar:
• Core: neutralize nucleus
• Valence: for bonding                   1s22s22p63s23p6
• For an s or p - block element                 Br:
   – Valence electrons are in last 2
     orbital                              [Ar]4s23d104p6
   – 8 slots
• For a d - block element
                                                Zn:
   – Valence electrons are the last
     d-orbital
                                       1s22s22p63s23p64s23d10
   – 10 slots
• Exceptions: p-block elements with
  d-orbitals before the “stair”                 Pb:
   – D-orbital AND p-orbital can be
     involved in bonding                  [Xe]6s25d106p2
                Valence Electrons
• Stability for s/p element:
   – Get 8 total like noble gas
   – Have all valence electrons on same energy level (n)
• Stability for d (transition) elements:
   – full, empty, or half full
• Fills up empty spots in orbital
   – Sharing electrons
   – giving up or taking electrons (ions)
• Valance shell – the outer most shell(s) involved in bonding
• Valance configuration – just shows the electrons present in
  the valance shell(s)
            Valence Configuration:
• For s/p element:
• Count the L the element is in and one L back
  – Last s and last p orbital of the configuration
  – Note: For groups 1 and 2, the p orbital comes first!
• For d element
  – Just d orbital
• For exception transitions:
  – Last d and p orbital
    Try: C, Br, Ca, Cu, Sn



1

2
3

4

5

6
7
                       A Pattern…
Element Element   Valence   Nearest NG     New config after
        Charge     config     config       adopting charge
  O
          -2      2s22p4      2s22p6             2s22p6
  Cl
          -1      3s23p5                        3s23p6
                              3s23p6
  Ca
                                         NG shortcut
          +2                                b4:      3s23p64s2
                  3p64s2      3s23p6
                                         New Valence:
                                                        3s23p6


                  What is the Pattern?
    Ions and Valence Configurations
• What is the valence configuration of Mg?
• Why is Mg still not “happy” even though it has 8
  total?
• An atom will become an ion in order to get the
  valance configuration of a noble gas
  – Has 8 total
  – All valence electrons on same energy (n) level
• For transitions, they will become a ion to be empty,
  full or half full
         Transitions: A special case
• Fe: [Ar] 4s23d6
• How can the 3d orbital become half full if there are
  6 electrons???
  – Fe+1 --> [Ar] 4s23d5
• Charges usually see:
  – +2, +3
  – Why??? And How???
• Electronic configuration does not explain bonding
  completely
• Need to include ML and Ms too!
• Need Orbital diagrams!!! :-)
               Orbital Diagrams
• Orbital diagrams show all
  quantum numbers for the       Fe:[As] 4s2 3d6
  valance configuration of      4
  elements                      s
• Use: To see what the atom’s
                                3
  electron arrangement looks
                                d
  like and sketch a bond in a
  compound
                  Orbital Diagrams
• How to draw an orbital diagram:     Valence Orbital Diagram of Fe
• Write out the valence configuration
• Sketch the L’s. Make sure to show               3d6
  the relative size if the n’s are
  different
• For each ML, make a line. Each ML
  holds a maximum of 2 electrons.
• The higher energy L must be written
  on top of the others
• For Ms: clock wise is shown as an
  up arrow, counter clockwise is
  shown as a down arrow. Up arrows
  are written on all possible ML’s
  first, then go back and pair with
  down arrows                         3d
                Orbital Diagram
• Try:
  – Cl, I, Ni

								
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