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Chapter 9 Chemical Bonding Theories Valence Bond Theory: Uses Lewis Structures Bonds form using shared electrons between overlapping orbitals on adjacent.

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Presentation on theme: "Chapter 9 Chemical Bonding Theories Valence Bond Theory: Uses Lewis Structures Bonds form using shared electrons between overlapping orbitals on adjacent."— Presentation transcript:

1 Chapter 9 Chemical Bonding Theories Valence Bond Theory: Uses Lewis Structures Bonds form using shared electrons between overlapping orbitals on adjacent atoms. Orbitals arrange around central atom to avoid each other. Two types of bonds: sigma and pi. Molecular Orbital Theory: Uses MO Diagrams Orbitals on atoms “mix” to make molecular orbtials, which go over 2 or more atoms. Two electrons can be in an orbital. Orbitals are either: bonding, antibonding, or nonbonding. Bonds are either: sigma or pi.

2 Orbitals on bonding atoms overlap directly between bonding atoms Sigma (  ) Bonding Between s orbitals Between p orbitals

3 Consider VSEPR Shapes and bonding: Sigma (s) Bonding

4 What’s wrong with this picture? Atoms bond by having their valence orbitals overlap

5 Orbitals don’t go in same directions as atomic orbitals. 2s 2p z 2p x 2p y Orbitals in CH 4 Orbitals on C

6 Orbitals don’t go in same directions as atomic orbitals. 2s 2p z 2p x 2p y Orbitals in CH 4 Conclusion: Atomic orbitals change shape when they make molecules.

7 Hybrid Orbitals Atomic valence orbitals “combine and mix” to form new “Hybrid Orbitals” Hybrid orbitals go in the VSEPR electron geometry directions.

8 Types of Hybrid Orbitals

9 Types of Hybrid Orbitals: 2 Pairs

10 Types of Hybrid Orbitals: 3 Pairs

11 Types of Hybrid Orbitals: 4 Pairs

12 Types of Hybrid Orbitals

13 Sigma Bonding Orbitals overlap directly between two nuclei:

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16 Sigma Bonding involves hybrid orbitals and/or H 1s orbitals. Pi bonding involves unhybridized p orbitals. Sigma vs. Pi Bonding

17 Pi Bond Formation

18 Bonding in Ethene

19 Bonding in Acetylene

20 Bonding in Formaldehyde

21 Bonding in Benzene

22 Advanced: Allene Each end carbon is a flat trigonal. Are they co-planar or perpendicular?

23 Bonding in Allene

24 Conformations vs. Isomers Isomers: Molecules with same formula but different structure Conformers: Different temporary shapes of the same molecule

25 Bond Rotations CAN happen around single bonds Cannot happen around double bonds

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27 Cis-Trans Isomerization When two groups are on a “side” of a molecule. cis trans

28 Can these molecules have cis-trans isomers?


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