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Monday April 8, 2024    Day 55
Lone Pairs and Molecular Geometry
Electronic vs. Molecular Geometries

Textbook Readings

10.3: VSPER Theory: The Effect of Lone Pairs
Course Lectures

10.5  pdf  Video    VSEPR Part II
Textbook Readings

10.2: VSEPR Theory
          and the five fundemental shapes. 		Review of VSEPR and the
Effect of Lone Pair Electrons

Objectives

1. Associate multiple  bonds as single regions
     of electron density

2.  Associate lone pair groups as single regions
     of electron density.

3. Determine the total number of regions of
    electron density from a Lewis structure
    and use this number to predict the
    electronic geometry for the molecule.

 		VSEPR and Bond Angle Distortion

4. Differentiate between lone pair and bonding groups to correctly provide the
    molecular geometry name.

5. Predict bond angles in situations where lone pair electrons and multi-bonds
    distort molecular frameworks.

Homework Problems

60.1   For each of the following 5 molecules....
         i.   Draw the Lewis Structure
         ii.  Determine the number of bonding regions, lone pair regions, the electronic geometry name,
               and the molecular geometry name.
         iii. Draw a molecular picture and identify all bond angles as to how they compare to ideal values.

         a. NH3          b. H2O          c.  CH2O         d. SF4          e. XeF4     

Click and drag the region below for correct answers

60.1
     a. Click HERE
     b. Click HERE
     c. Click HERE
     d. Click HERE
     e. Click HERE
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Tuesday   April 9, 2024    Day 56
Calculation of Dipole Moments and Percent Ionic Character

Textbook Readings

10.5: Molecular Shape and Polarity
Course Lectures

10.6  pdf  Video    Dipole Moments
Objectives:

1. Calculate extreme dipole moment values
    bond lengths and the charge of an electron.

2.  Calculate experimental dipole moment values
      given bond lengths and measured charge
      separation values.

3.   Determine "Percent Ionic Character" given
      appropriate information.

 Dipole Moment Calculations -
Basic Concepts
Homework Problems

         The dipole moment (μ) of a covalent bond is a measure of the bond's polarization. 
         The dipole moment depends on both the charge separation (q: Coulombs) and the bond
              length (r: meters) in the following way:
μ    =     q   ×    r

           Most often, dipole moments are reported in units of debye (D)  where
1 D = 3.3356 ×  10-30  C*m

61.1  Initially, let's assume an entire electron has moved from one side of the bond to the other.
         This is an idea consistant with complete electron transfer and the formation of a purely
         ionic bond...  a very "extreme" and rare situation. 

         Use the charge of a whole electron (1.602176 x 10-19 C)  and the following bond lengths to
         determine the hypothetical extreme dipole moment (μextreme)  of each bond
          in C*m and "D" units.      Show your work.

                            H-F bond    Bond length  = 0.92  x 10-10 m
                            H-Cl bond   Bond length = 1.27 x 10-10 m
                            H-Br bond   Bond length = 1.41 x 10-10 m
                            H-I bond      Bond length = 1.61 x 10-10 m

                       
61.2  In problem # 61.1, we assumed an entire electron's charge existed across the bond.  However,
         in experiments designed to measure charge  separation across the bond, the following "q"
         values were experimentally determined for each of the bonds above:

                            H-F bond     q = 6.5987 x 10-20 C
                            H-Cl bond   q = 2.8366 x 10-20 C
                            H-Br bond   q = 1.9399 x 10-20 C
                            H-I bond      q = 9.1159 x 10-21 C

          Use these charge values and the bond lengths from 61.1 to recalculate the experimental dipole
          moments for each bond in units of Debye.

61.3   The "Percent Ionic Character" describes just how much a bond is or isn't like an ionic bond.
          Small percents suggest a more covalent bond while values closer to 100% represent ionic
          bonds. 

          The "Percent Ionic Character" is calculated by comparing the experimental dipole
          moment (μexp) to the ionic extreme (μextreme) given your answers to 61.1.  It is calculated as follows:

                                                                    μexp
               Percent Ionic Character =   ------------    x   100      
                                                                 μextreme

          Calculate the percent ionic character of each bond.
         
61.4    Determine the  ΔEn values (Day 53) and compare to the Percent Ionic Character values.
           What is the connection between Percent Ionic Character,  ΔEn and bond type?

Click and drag the region below for correct answers

61.1        H-F         μextreme               =    1.474  x 10-29 C*m     =   4.42 Debye
              H-Cl         μextreme              =    2.035 x  10-29 C*m     =   6.100 Debye
              H-Br        μextreme              =    2.259 x  10-29 C*m     =   6.772 Debye
              H-I            μextreme              =   2.579 x  10-29 C*m     =   7.732 Debye


61.2       H-F           μexp      =     6.07  x 10-30 C*m     =   1.82 Debye
              H-Cl         μexp        =   3.602 x  10-30 C*m     =   1.080 Debye
              H-Br         μexp        =   2.735 x  10-30 C*m    =   0.8200 Debye
              H-I            μexp       =    1.468x  10-30 C*m      =   0.440 Debye


61.3       H-F     Percent Ionic Character  =   41% ionic
              HCl     Percent Ionic Character =    18% ionic
              HBr     Percent Ionic Character =    12.1% ionic
              HI        Percent Ionic Character =    5.69% ionic

61.4       HF:    ΔEn  =   1.9  .... tells us of a very polar covalent bond (0.4 - 2.0 range)
                         % Ionic Character = 41%   ... a lot of ionic character but not
                                                                             quite into the ionic range (50%)

              HF:    ΔEn  =   0.9  ....tells us a midrange polar covalent bond (0.4 - 2.0 range)
                         % Ionic Character = 18%   ...low amount of ionic characeter

              HF:    ΔEn  =   0.7  ....tells us of a midrange polar covalent bond (0.4 - 2.0 range)
                         % Ionic Character = 12.1%   ...low amount of ionic characeter

              HF:    ΔEn  =   0.4  ....tells us it's just barely a polar bond
                         % Ionic Character = 5.69%   ... very small amount of ionic character

       These results are consistant.  As the % Ionic Character goes up, the bonds become more and
       more polar as evidenced by ΔEn  values
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Wednesday April 10, 2024    Day 57
Bond Polarity and Molecular Polarity: Net Dipole Moment

Textbook Readings

7.6 Molecular Shape and Polarity
Course Lectures

10.6  pdf  Video    Dipole Moments
10.7  pdf  Video    Molecular Polarity
Objectives:

1.  Identify polar and non-polar BONDS using
     ΔEn values .

2. Identify symmetric and non-symmetric
     distributions around a center-most atom.

3.  Create bond dipole moment vectors (arrows)
     for a given molecule and add them (head to
     tail) for the molecular dipole moment.

4.   Label a molecule's positive and negative ends.

 		Polar Molecules Tutorial: How to determine polarity in a molecule

Homework Problems

62.1   Use the video above to document the molecular dipole moments for the molecules listed below.
           Be sure to include these details: 
                                            i. molecular 3D framework with bond dipoles drawn carefully and to scale
                                            ii. Separate head - to - tail addition of bonding dipole moments (vectors)
                                            iii.  δ+ and δ- labels indicating the molecule's positive and negative sides.

Molecules: a. H2O              b. SF2                 c. CO2                 d. SCO               
                  
                    e. BF3              f. BF2Cl               g. BFCl2             h. BCl3
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Thursday April 11, 2024    Day 58
Bond Polarity and Molecular Polarity: Net Dipole Moment Part 2

Textbook Readings

7.6 Molecular Shape and Polarity
Course Lectures

10.6  pdf  Video    Dipole Moments
10.7  pdf  Video    Molecular Polarity
Objectives:

1.  Identify polar and non-polar BONDS using
     ΔEn values .

2. Identify symmetric and non-symmetric
     distributions around a center-most atom.

3.  Create bond dipole moment vectors (arrows)
     for a given molecule and add them (head to
     tail) for the molecular dipole moment.

4.   Label a molecule's positive and negative ends.

 		Polar Molecules Tutorial: How to determine polarity in a molecule

Homework Problems

63.1   Use the video above to document the molecular dipole moments for the molecules listed below.
           Be sure to include these details: 
                                            i. molecular 3D framework with bond dipoles drawn carefully and to scale
                                            ii.  δ+ and δ- labels indicating the molecule's positive and negative sides.

Molecules:      a. CH4              b. CH3F               c. CH2F2                 d. CHF3              
                  
For the following molecules (e - h), the fluorine atoms
occupy the equatorial positions in the trigonal bi-pyrimidal electronic geometry.

                         e. PCl5              f. PFCl4               g. PF2Cl3            h. PF3Cl2
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Friday April 12, 2024    Day 59
Valence Bond Theory Part 1

Textbook Readings:

10.6: Valence Bond Theory:
          Orbital Overlap as a Chemical Bond

10.7: Valence Bond Theory:
          Hybridization of Atomic Orbitals
Course Lecture

10.8  pdf  Video    Valence Bond Theory 1
Objectives

1. Explain what is meant by atomic orbital
     overlap and how it's responsible for
     H - H bond formation.

2.  Identify the limitations of simple atomic
     orbital overlap and the need for a
     new theory.

3.   Describe what is meant by a "promoted
      electron"  and what it accomplishes for
      bonding in the BeCl2 molecule.
10.8 Valence Bond Theory 1



4.   Illustrate orbital overlaps that represent covalent bonds for different molecules and
       identify bond angles.

Homework Problems

63.1   Hydrogen molecule formation
          a. Draw the electron ladder diagram for a neutral hydrogen atom.

          b.  Draw a picture of two separate hydrogen atoms. 
               Clearly indicate the electron in the spherical 1s orbital.
              
          c.   Draw a new picture of the two hydrogen atoms with orbital overlap.   Position the
                electrons between the two nuclei (the covalent bond)

63.2  BeH2
          a.   Draw the electron ladder diagram for a neutral berylium atom.

          b.   Bond formation requires unpaired electrons.  Where are the electrons in the neutral
                berylium atom?  Are they all available for bonding?

          c.   Draw the electron ladder diagram for the "promoted state" berylium atom.
                This will require spliting up the two, 2s electrons and moving one up to the 2p.

          d.   Draw the electron ladder diagram for the "hybrid state" berylium atom.
               
          e.   Valence bond theory blends or mixes atomic orbitals.  In the case of BeH2, the 2s
                and 2px atomic orbitals are mixed together to form two "sp" hybrid orbitals.
                Draw both hybrid orbitals using "Be" to identify the nucleus.  Also, identify
                the single electron in each hybrid orbital.

          f.   Draw both sp hybrid  orbitals around one common Be nucleus.  
                Use a two different colors to identify one sp hybrid from the other.

          g    Re-draw your answer to part "f".  Overlap the two hydrogen atom's 1s orbitals with
                each of the "Be" sp hybrids.  Clearly indicate the electrons that form the single bonds.
                These bonds are known as "sigma: σ" bonds because the overlap exists on the axis that
                connects the two atoms.

          h.   Use arrows to indicate the bond angle in your answer to part "g".

63.3   BH3
         
          a.   Draw the electron ladder diagram for a neutral boron atom.

          b.   Bond formation requires unpaired electrons.  Where are the electrons in the neutral
                boron atom?  How many are available for bonding?

          c.   Draw the electron ladder diagram for the "promoted state" boron atom.
                What is the purpose of promoting an electron?

          d.   Draw the electron ladder diagram for the "hybrid state" boron atom.
                This will require spliting up the two, 2s electrons and moving one up to the 2p.

          e.   Valence bond theory blends or mixes atomic orbitals.  In the case of BH3, the 2s
                2px and 2py atomic orbitals are mixed together to form three "sp2" hybrid orbitals.
                Draw all three  hybrid orbitals using "B" to identify the nucleus.  Also, identify
                the single electron in each hybrid orbital.

          f.   Draw all three  sp2 orbitals around a common B nucleus.   Use different colors to
                identify each hybridized orbital

          g.    Re-draw your answer to part "f".  Overlap the three  hydrogen atom's 1s orbitals with
                each of the three sp2 hybrids.  Clearly indicate the electrons that form the sigma bonds.

          h.   Use arrows to indicate the bond angle in your answer to part "g".


Click below for answers.

63.1       63.2         63.3
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