Select Page

## Q3 : Week 5 – 3/5 – 3/9

If you have not already please join the REMIND for this class.

Make Sure Powerschool grades are accurate!!

______________________________________________________                                                   Jump to:  Monday Homework            3/6 – Monday – A Day – 2/3a Lab, 4

Main focus –

a) To introduce MO theory, a non- valence bond theory.

b) To complete a MO diagram.

c) To compare BO, bond lengths, and bond energies by MO diagrams.

Period 2/3a:

1. Potential Energy Internuclear distance Diagram

Complete the Potential Energy Internuclear distance Diagram Use diagram to explain Bond Energy and Bond Length with chart posted this week.

Potential Energy Internuclear distance Diagram.pdf

Run through slides 36 – 39:

3. Lattice Energy  Lets Remember that we have ionic compounds that are in the mix.  They are ions attracting themselves in a crystal lattice and are not part of the hybridization or polarity discussion.  Because all ionic compounds are solids (in crystal arrangements) at STP we use lattice energy to describe their stability or strength of ionic character.  Much like we use the difference of electronegativity for the dipole moment of each polar bond in covalent (molecular) compounds.

4.  Add to the Take- home – collect

5.  Review the need for another theory other than the valence – bond theories that we have been studying

a)  Mo Presentation – modeling Diatomic homonuclear MO Diagrams

b)  Selected correlation graphs (Li2 – C2) – These were in the student presentation “MO Bonding “

bonding 5a MO Yo classwork!.pdf

Used this worksheet after the “MO Bonding”
bonding 5 MO Yo! oxygen and nitrogen.pdf

MO – N2 vs N2+.pdf

6. Review Last nights Form:

MO Theory Form 1920 – Key p.pdf

Period 4:

Skip 1 – 4.

5 – 6 above.

Lattice Energy presentation:

_______________________

TODAY’s NOTES:

Class Notes on the limitations of the Valance Bond Theories:

Valence bond theories that we learned:
1: Covalent bonds – sigma, pi bonding
2: VSEPR theory – (electron orbitals repelling to form equidistance stable geometries)
3: Lewis Dot structures
4. Hybridization

Our valence bond theories = hybridization, VSEPR, Lewis dot diagrams have limitations as we have seen.  How does the chlorate ion have resonance if it is sp3 hybridized and there are no un-hybridized p orbitals to pi bond with?

Remember that dots on a piece of paper can give us so much information for many molecules some complex but some our rules of formal charges that help guide us to the best structure guide us to structures that actually do not exist based on their properties found experimentally!

Here is an example of the sulfate ion, SO4-2

THE LEWIS DIAGRAM BELOW REPRESENTS THE BEST LEWIS DOT STRUCTURE BASED ON FORMAL CHARGES.  Below each sulfur has a Formal charge of ZERO!
Above is what our valence bond theory predicts using the rules of Formal Charges and etc.  THIS IS NOT WHAT WE FIND experimentally!!! Actually the lewis diagrams that we find from experimental evidence looks like the following.

The sulfur below has a Formal Charge of +2 and yet it is the structure we identify experimentally!

WHAT???  How can it exist more like this structure when clearly is breaks the rules of Formal Charges (+2) on the Sulfur atom?  Actually the charge is measured to be +1.77 on the sulfur in experiments.  What gives?  The bonding is neither covalent nor ionic it is something in between..

So we are at the end or the limits of this valence bond theory. We were were always going to be limited by a theory that treats electrons as dots when we have learned from electrons exist as waves!!!

OK so what if we run into a Lewis Diagram that is beyond the Valence Bond Theory?
The Current AP Curriculum does not support using Formal Charges to provide guidance in building lewis dot diagrams that are beyond the Octet Rule.  The rest of the world does so we make the following rule when dealing with AP:

If there is a element that exists in row three and beyond then the octet rule takes preference:
Does experimental evidence support this rule completely? No.  Does experimental evidence support the use of formal charges completely? No.  We need a new theory!

Example:  SO4- , SO3
So lets learn a new theory that picks up where valance bond theory leaves off.  It is called MO theory or molecular orbital theory and it treats electrons as waves!

MO and Gap Theory:

3/6 – Monday’s Homework: –

1.  Please view the MO Theory to Band Theory lecture below.

2. Please complete the Gap or Band Theory Form below:

1 :MO theory to Band Theory:

2 : Gap or Band Theory Form:

>

3/7 – Tuesday – B Day – 2, 3b/4 Lab

Main focus –

a) To

b) To

c) To

Period 2 3/4:

1

2. HI strongest acid?

3/7 – Tuesday’s Homework: –

2.  Plea

3/8 – Wednesday – A Day – 2/3a Lab, 4

Main focus –

a) To

b) To .

c) To

3/8 – Wednesday Homework:

1. Make

2. Watch

3. Then

3/9 – Thursday – B Day – 2, 3b/4 Lab

Main focus –

a) To

b) To

c) To

Period 2:  –

1:  Comp

2.  Expand

3/9 – Thursday Homework: –

1.

OK

3/10 – Friday – A Day – 2/3a Lab, 4

Main focus –

a) To

b) To i

Period 2/3 /4–

1.

4: L

3/3 – Weekend Homework: –

1. P

2. Ple

_____________________