Wed, Oct 29 th 2008 Today’s Agenda

1. Wed, Oct 29th 2008Today’s Agenda Nature of Chemical Bonds 4.2 Reviewing electron configuration-(Quantum Numbers) Hybridization 4.2 SP2 , SP3, SP hybrid orbitals

2. The Nature of The Chemical Bond • Mr. LinusPauling – Valence Bond Theory • Covalent bond is formed when two orbitals overlap (share the same space) to produce a new combined orbital containing two electrons of opposite spin. • Consider H2

3. The Nature of The Chemical Bond • Linus Pauling – Valence Bond Theory • Covalent bond is formed when two orbitals overlap (share the same space) to produce a new combined orbital containing two electrons of opposite spin. • Consider H2

4. The Nature of The Chemical Bond • Linus Pauling – Valence Bond Theory • Covalent bond is formed when two orbitals overlap (share the same space) to produce a new combined orbital containing two electrons of opposite spin. • Consider H2 • σ sigma bond formed between the two 1s orbitals

5. The Nature of The Chemical Bond • Let’s examine BH3 • Electron Configuration for H is • B 1S22S22Px1 • H 1S1 • How can you have 3 bonds around Boron ?? • According to electron configuration of Boron, only 1 lone electron on 2Px , should that allow B to form only 1 bond? • ANSWER: NO, Boron can form 3 bonds, this suggest something else is occurring. • Hybridization

6. Hybridization (sp2) • The combination of two orbitals of similar energy level (n) to create more stable hybrid orbitals. • Boron 1s22s22px1

7. Hybridization (sp2) • The combination of two orbitals of similar energy level (n) to create more stable hybrid orbitals. • Boron 1s22s22px1 • An electron is being promoted to 2P orbital

8. Hybridization of Boron

9. Hybridization (sp2) • The 2s orbital is mixed (combined) with two of the 2px,2pyorbitals resulting in three hybrid orbitals – these three new hybrid orbitals are named sp2 • The name of these hybrid orbitals is derived from their “parent orbitals” s & p • The superscript on the p, indicates the number of p orbital involved in this mixing process. This case: two of the p-orbitals are involved in mixing, that is why we need to write p2

10. How does that look on BH3

11. Hybridization (sp3) • Let’s examine methane CH4 • What is the electron configuration for Carbon • C 1s22s22px1py1 • Prior to understanding Hybridization, how many bonds do you think Carbon are allowed to form? 2 or more than 2 ? • Why more than 2 ? • Hybridization – now that you have learned about hybridization you can explain how Carbon can have a total of 4 bonds.

12. Hybridization (sp3) • Let’s explain why Carbon can have four Hydrogen bond to it using hybridization. • Step 1. Electron Configuration (of central atom) • Step 2. Put the electron configuration on an energy level diagram • Step 3. Promote electrons from the next-lower orbital (ℓ) within the same energy level (n) • Step 4. Mix all of the occupied parent orbitals together to create new hybridized orbitals. *** • Step 5. Name these newly formed hybrid orbitals using the parent name and superscript to indicate how many of each parent participated.

13. Hybridization (sp3)

14. sp3 In terms of energy 2p Hybridization Energy 2s

15. How is it look like when 4 H bond with Carbon? • Draw the four sp3hybridized orbital overlapping with the 1s orbital of four hydrogen.Try that !

16. What is the geometry (that VSEPR shapes) for sp3 hybrid orbitals • 4 bonds, 0 lone pair, total = 4 • Tetrahedral

17. How do you explain multiple bond? • C2H4 what will the orbitals of Carbon hybridized into ? • Let’s attempt to write H2C-CH2 as single bond. • We know that when Carbon hybridize there will be four sp3 hybrid orbitals. • And that each of these orbitals can form sigma bond with a Hydrogen. • If we propose H2C-CH2 as a single bond, that was only three sp3orbitals, what happened to the fourth one? • This is when the “Mixing” step in Hybridization decided to mix differently.

18. How do you explain multiple bond?(formation of sp2 hybrid orbitals) • Carbon still get its promotion! • But is now mixed differently!!! • The 2s1 electron is now mixed with only two of the three 2P3 electron (2Px1 & 2Py1) forming three sp2 hybrid orbitals (on the same plane) – two of Carbon’s sp2 orbitals are bonded with two H, and the third sp2 orbital is bonded with its neighbor Carbon. • 2Pz1 decided not get involve in sigma bonding. (simply, there is just not enough H for it to bond with.) • It stays in its own 2Pz orbital. (which is on a different plane, the z-plane) – • Until it meets its right partner which is another 2Pz1 from the Carbon next door. • Pi bond is formed. π

20. How about triple bond? • Can we use hybrid orbitals to explain triple bonds? • Take C2H2, ethyne for example • Again, Carbon still get its promotion. • But “Mixes” differently • in ethyne, C2H2 there is only one hydrogen for each carbon. • Let’s propose it was a single bond H-C-C-H • Carbon will have two sp hybrid orbitals and two normal 2py1 2pz1 • The two hybrid orbitals (sp) , one is bonded to H, the other is bonded to C. • The two electrons 2py1 & 2pz1 will form two π bonds with the Carbon next door.

21. Hybridization for triple bonds(formation of sp hybrid orbitals) • Let’s try ethyne, C2H2 • Draw Energy Level Diagram for central atom. • Promote & Mixes (keep in mind, what we have said about electron don’t want to participate in the mixing process. (recall: they are the 2py1 &2pz1 electrons)

22. Orbit-Wise How Will C2H2 Look? • Try drawing the orbitalsyourself!!!

23. Triple bond