Part Three: Molecular Orbitals, Hybridization and Geometry

  1. Atomic orbitals
    1. Remember these subshells from general chemistry?
      1. s
      2. p
      3. d
      4. etc.
    2. Each subshell has a certain number of atomic orbitals (represented by the lines below)
      i. s --   one orbital
      ii. p --  three orbitals
      iii. d -- five orbitals
    3. Each atomic orbital can accommodate two electrons
  2. Hybridization
    1. A hybrid or a mix of atomic orbitals
    2. An atom's orbitals can interact with other atoms and overlap to form a given hybrid atomic orbital
      For example- here the sp hybrid atomic orbital is formed:
  3. Molecular Orbitals
    1. Molecular orbital =overlap of two atomic orbitals from different atoms
    2. There are two types of bonds formed in molecular orbitals: sigma bonds and pi bonds.
    3. sigma bond (σ)= overlap of hybridized orbitals along the line between nuclei
      1. single bonds are sigma bonds
      2. double and triple bonds each have one sigma bond
    4. pi bond (π) = sideways overlap between two p orbitals
      1. double bonds have one pi bond
      2. triple bonds have two pi bonds
      3. there must be a sigma bond in order for a pi bond to occur
    5. Summary Chart

      6. Bond Sigma bonds Pi bonds Total
      Single 1 0 1
      Double 1 1 2
      Triple 1 2 3

  4. Geometry
    1. An atom has a given hybridization depending on the number of bonds extending from it
    2. There is also an implicit geometric shape associated with the hybridization
    3. Furthermore, the bond angles formed are important
    4. Here is a chart that sums this up:

    Bond Hybridization Geometry Bond angle Picture
    Single sp3 Tetrahedral 109.5°
    Double sp2 Trigonal planar 120°
    Triple sp Linear 180°

  5. Ways carbon can bond to others
    1. Option #1: Carbon may accommodate four single bonds
    2. Option #2: Carbon may accommodate one double bond and two single bonds
    3. Option #3: Carbon may accommodate two double bonds
    4. Option #4: Carbon may accommodate one triple bond and one single bond

Part Three Exercise Set

Instructions:

  • Use what you learned in Part Three to complete the following exercises.
  • Exercise #1: The arrows point to different carbon atoms in the following molecule that are lettered a, b and c. Determine the hybridization and bond angles for each. The arrow points to the vertex of the angle formed.
  • Exercise #2: The arrows point to different bonds in the following molecule that are numbered 1, 2 and 3. Determine the bond type and the number of sigma bonds (σ) and pi bonds (π) for each.
  • We recommend you draw your response on plain white paper. When ready, click on the window to reveal the answer.

Exercise #1


Arrow Hybridization Bond Angle with arrow at vertex
a
sp2
120°
b
sp
180°
c
sp3
109.5°

Exercise #2


Arrow Bond type Number of sigma bonds Number of pi bonds
1
double
1
1
2
triple
1
2
3
single
1
0