Unit 4 Bonding Theories

O = O O = O VSEPR Theory Valence Shell Electron Pair Repulsion Predicts the shapes of covalent molecules The repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible. O = O O = O

VSEPR Theory In your notes, create a chart to help you learn the various shapes, bond angles, etc. SHAPE # BONDS # LONE PAIRS BOND ANGLE EXAMPLE PICTURE HYBRIDIZATION

- - Molecular Shapes 180o 120o 104.5o 109.5o 107o SHAPE DESCRIPTION ILLUSTRATION Linear Bond Angle = 180o One or two bonding pairs, no lone pairs - - X A 180o X A 104.5o Bent Bond Angle = 104.5o Two bonding pairs, two lone pairs X A 107o X A 120o Trigonal Planar Bond Angle = 120o 3 bonding pairs, no lone pairs X A 109.5o Trigonal Pyramidal Bond Angle = 107o 3 bonding pairs, one lone pair Tetrahedral Bond Angle = 109.5o Four bonding pairs, no lone pairs

Lone Pairs Take up MORE space SQUEEZE the bond angle X A X A

HF CH4 Practice: Determine the shape of each molecule: LINEAR TETRAHEDRAL

More Practice: BF3 NH3 SeCl2 TRIGONAL PLANAR TRIGONAL PYRAMIDAL BENT F

Molecular Shapes cont. The shapes we have looked at all had at most 4 bonding sites. However, there are MANY compounds that have MORE than 4 bonding sites. Therefore, there is the possibility for many more types of geometry.

Molecular Shapes cont. Shape Atoms on Lone Pairs Example central atom Trigonal 5 0 PCl5 Bipyramidal Bond angle: 90o and 120o See Saw 4 1 SF4 Bond angle: 180o and 120o

Molecular Shapes cont. Shape Atoms on Lone Pairs Example central atom T-shaped 3 2 BrF3 Bond angle: 90o Linear 2 3 Bond angle: 180o I3

Molecular Shapes cont. Octahedral 6 0 SF6 Bond angle: 90o Shape Atoms on Lone Pairs Example central atom Octahedral 6 0 SF6 Bond angle: 90o Square Pyramidal 5 1 BrF5 Bond Angle: 90o

Molecular Shapes cont. Shape Atoms on Lone Pairs Example central atom Square Planar 4 2 XeF4 Bond Angle: 90o

Hybrid Orbitals Review – what is the electron configuration of Carbon? 1s2 2s2 2p2 The orbital notation is: ____ ____ ____ ____ ____ There are only 2 places for other atoms to bond…..but we know carbon can bond with 4 things. So, Carbon will hybridize or move its electrons around to make more available spots for bonding.

Hybrid Orbitals Ex. Carbon 2p ___ ___ ___ sp3 ___ ___ ___ ___ 2s ____ Now carbon has 4 available bonding sites, and all are of equal energy.

Hybridization There are 4 possible locations for bonding, or 4 charge clouds. sp3 hybridization can lead to the following types of geometry: Tetrahedral Trigonal Pyramidal Bent Ex. 1 CH4

Hybrid Orbitals example sp3 hybridization Ex 2. NH3

Hybrid Orbital Example Ex 3. Water – H20 Draw the Hybrid orbitals

Hybrid Orbitals sp2 Hybridization What is the electron configuration for Boron? 1s2 2s2 2p1 How many bonding sites does Boron have? So….the orbitals need to hybridize to reflect the correct number of bonding sites (or charge clouds).

Hybrid Orbitals Ex. BF3 – notice that only 2 of the p orbitals hybridize, the 3rd p orbital remains unchanged (and at the higher energy.)

Hybrid Orbitals sp Hybridization Can you determine what orbitals will be hybridized? How many charge clouds will there be? Note that the energy is now HIGHER than the s orbital, but LOWER than the p orbital.

Hybrid Orbitals There is currently a debate among scientists as to whether d orbitals hybridize or not. For the AP exam, hybridization of d orbitals is NOT required info. However, it IS important to know how potential d hybridization correlates to molecular geometry. Therefore, we will look at the number of charge clouds (bonds to central atom + lone pairs) and compare that to molecular shapes.

Sigma and Pi bonds Single bonds can also be referred to as sigma bonds. (σ) Where the two bonds overlap is the covalent bond – where they are sharing electrons.

Sigma and Pi Bonds When there is a double (or triple) bond, the 2nd (or 3rd) bonds made are pi (π) bonds. Pi bonds

Sigma and Pi bonds Count ALL the bonds in C2H2

Agenda Check homework Learn how to hybridize orbitals when double and triple bonds are involved Go over homework (as needed) and molecular geometry worksheet from yesterday VSEPR matching in groups

Hybridization cont. The first bond that is made is a single (or sigma) bond. Sigma bonds are made in hybridized orbitals. If a Pi bond is made, it will do so in an unhybridized orbital. Ex. CO2

Hybridization cont. Ex. NO2-