Multiple Bonds and Hybridization

1. Multiple Bondsand Hybridization

2. Multiple Bonds and Resonance • We’ve already looked at making double bonds • They need to be made in order to satisfy the octet rule for all atoms • Because they can be made in different spots to satisfy the octet rule, multiple bonds leads to resonance.

3. Nitrogen Gas (N2) How many electrons does each nitrogen have? How many does each one want? A single bond won’t do, and a double bond doesn’t do it either. Buuut, we can share 3 pairs of electrons (6), and then each nitrogen only needs 2 more.

4. Ethyne (C2H2)

5. Quadruple Bonds? We can make bonds with 1, 2, and 3 pairs of electrons, so could two atoms share 4 pairs of electrons? It seems like they should be able to, but as we’ll see, it doesn’t happennaturally, and this has todo with the “shapes” ofbonds.

6. Hybridization What do you think of when you hear “hybridization”? Now, since we’re talking about bonding, which involves electrons, what do you think is “hybridizing”? (Hint: where are electrons found in an atom?) Hybridization is a theory to explain the compositions and shapes of molecules that we already know exist.

7. Methane (CH4) • Hybridization is a great example of how we try to explain what we observe. • What we know about methane: • It exists. • Each hydrogen makes a single bond withcarbon (4 bonds) • The molecular shape (which is?) • The electron configurations ofhydrogen and carbon • According to the electronconfiguration, how manybonds can carbon theoreticallymake?

8. We have 4, but we can only have 2 • So, there are two possibilities. Either… • Methane doesn’t exist • OR • Carbon isn’t acting the way we think it should • Obviously, methane exists. Otherwise, the natural gas industry would have a lot less to work with. • So we have carbon acting strangely – this is where hybridization comes in.

9. Hybridizing In order to make four bonds, carbon needs to have four unpaired electrons in its configuration. The orbitals that carbon has just aren’t going to work – even if we put one in each, the shape will be wrong. We already know methane is tetrahedral. So, we hybridize the orbitals we are working with. We have four orbitals, one for each bond (2s, and three 2p) Just like the law of conservation of mass, orbitals can neither be created nor destroyed. This means if you put 4 orbitals in, you’ll have to get 4 back.

10. sp3 Hybrid Orbitals What we get are called hybrid orbitals, and are named based on the orbitals used to make them. For example, if you use one 2s and three 2p orbitals, you’ll end up with four 2sp3orbitals. Now, if you’ve got four bonding orbitals and they all want to repel, what shape do they take?(Hint: what is the shape of methane?)

11. sp2Hybrid Orbitals

12. sp orbitals 2 orbitals means linear. Notice how all of these correspond to the VSEPR shapes we just went over? This is because the hybrid orbital theory is what determines the VSEPR shapes.

13. Hybridization Shapes http://www.mhhe.com/physsci/chemistry/animations/chang_2e/hybridization.swf

14. Multiple Bonds • In covalent bonding, there are two kinds of bonds. • The bond that results from overlapping orbitals is called a sigma bond (σ bond). There is always a σ bond – this is the bond that forms a single bond. • The other type of bond is called a pi bond (π bond). This results from p orbitals that are above and below (one πbond) and on the sides (the other πbond) • http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom5s2_6.swf