Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories When bonding occurs, atomic orbitals overlap to produce molecular orbitals. Below is an example of “s” orbitals overlapping forming a sigma-bonding molecular orbital. H H A sigma bond is the result of a molecular orbital that is symmetrical around the axis connecting the atomic nuclei.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories Another example of a sigma bond: F F

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories An oxygen molecule has two types of bonds, sigma and pi. Pi bonds are not symmetrical around the bonding axis.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories A nitrogen molecule has one sigma and two pi bonds.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories “VSEPR” stands for Valence Shell Electron Pair Repulsion Theory. In general, this theory states that electrons within molecules repel each other. The amount of repulsion is dependent upon whether or not the electrons are in bonds. * Electron pairs will position themselves as far from other electron pairs as possible* Levels of Repulsion Example: H2O Strongest: Un-shared:Un-shared Repulsion Stronger: Un-shared : Shared Repulsion Strong: Shared : Shared Repulsion O H H

O H H O C O 1800 104.50 Test Your Knowledge Why is H2O a bent molecule while CO2 is a linear molecule? O O C O H H 1800 104.50 Bond Angle Bond Angle Water has more forces of repulsion acting on the bonded Answer:_______________________________________________________________________________ electrons than does carbon dioxide.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories The pictures below show why water and carbon dioxide are shaped differently, even though each molecule contains 3 atoms.

N F H H B H F F 1200 107.30 Test Your Knowledge Which molecule will exhibit the larger bond angles, and why? N F 1200 H H B H F F 107.30 BF3 has the larger bond angles because it has the least Answer:_______________________________________________ ______________________________________________________ amount of electron pair repulsion (No unshared-pair repulsion).

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories *Electron pairs always seek the furthest distance from each other!!

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories Molecular Shapes

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories Hybrid orbitals are orbitals of equal energy produced by the combination of two or more orbitals on the same atom. For Example: Carbon Hybridization 4 hybrid orbitals 1s 2s 2p 1s 2sp3 When the “s” orbital combines with 3 “p” orbitals, it is called sp3 hybridization. *Hybridization helps explain the bonding and geometry of many molecules .

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories Hybridization 2s 2p 2sp3

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories sp3 Hybridization * Hybridization is another way of understanding why molecules take on the shapes that they do. *Central atoms that have 4 areas of electron density within a molecule will exhibit sp3 hybridization.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories When the “s” orbital combines with 2 “p” orbitals, it is called sp2 hybridization.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories *Central atoms that have 3 areas of electron density within a molecule will exhibit sp2 hybridization.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories (C2H4) Ethene and "sp2" Hybridization Sigma Bond Sigma Bond Sigma Bond Sigma Bond Sigma Bond

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories A pi bond occurs when the overlapping orbitals do not lie directly on the bond axis, as seen in the picture below. Pi bonds only occur in double and triple covalent bonds. Double bond: 1 sigma & 1 pi bond Triple bond: 1 sigma & 2 pi bonds

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories *When the “s” orbital combines with 1 “p” orbital, it is called sp hybridization.

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories *Central atoms that have 2 areas of electron density within a molecule will exhibit sp hybridization. sp Hybridization

Chapters 8 , 9 & 22: Covalent Bonding and Naming Compounds Sec. 8.3: Bonding Theories Pi bonds in Ethyne (C2H2) Each Carbon Atom has 2 areas of electron density. sp hybridization H C C H How many pi bonds are in ethyne? ___________ Two