-Understand how the absence or presence of lone pairs of electrons affects the geometry of a molecule

-Know what the various geometries are and how to predict them

-Understand the concept of orbital hybridization and how it changes the bonding in an atom such as carbon(NEXT LECTURE)

The arrangement of atoms within a given molecule.

( Section 8.3 232-236 in your textbook)

Valence Shell Electron Pair Repulsion = VSEPR

Assumption: Electron pairs repulse each other

Consequences

1)This repulsion of electron pairs causes them to orientate as far from each other as possible.

2)Atom centers also want to be as far apart as possible

2 Bonding pairs

0 lone pairs

AX2

..

2 Bonding pairs

2 lone pairs

:AX2:

3 Bonding Pairs

0 lone pairs

AX3

3 bonding pairs

One lone pair

:AX3

4 bonding pairs

0 lone pairs

AX4

Summary of Five Main Geometries

Linear Formula= AX2

Bent Formula = : AX2 :

Trigonal Planar Formula = AX3

Trigonal Pyramidal Formula = : AX3

Tetrahedral Formula = AX4

Note: A –represents the central atom

X – represents the attached atom

• 5 cards in your packet … one for each geometry.

• As a group, use your whiteboards to draw the Lewis dot structure for each one of your compound cards.

• Once you have the Lewis Dot structure, use it as a guide to construct a model of the compound.

• I will walk around and check your Lewis Dot structures and models.

• Create a group sheet to record those Lewis Dot structures/models that you are having trouble with.

• We will have cool down that you will hand in today (exit

slip)

Groupwork norm I will also be assessing ….

Every student contributes when every student feels safe to make

mistakes in the group.

What the fudge?! DON’T JUDGE!

Hybridization

The electron structure of a carbon atom can be written as:

Based on this model, we would predict that carbon atoms should form two covalent bonds??!!

Instead carbon atoms almost always form 4 bonds.

Why????

Hybridization

hybridization

1 s + 3 p = 4 sp3

(All 4 orbitals are now equal at the 2nd energy level)

Regular Carbon Aufbau Diagram Hybridized Carbon Aufbau Diagram

Electrons must be distributed among the new orbitals. Since these hybrid orbitals are equal in energy, the electrons must distributed according to Hund’s Rule.

4 sp3 orbitals

4 sp3 orbitals bond with4 hydrogen atoms - methane

sp3 carbon

Overlap hereis known assigma bond

sp2 hybridization

sp2 hybridizationcarbon double bond - ethene

sp hybridization

sp hybridizationcarbon triple bond - acetylene

sp hybridizationcarbon triple bond - acetylene

234-236 in your text discusses these examples