Review Double and Triple Bonds

1) Make your regular Lewis Structure with all single bonds and full octets

2) Count up the number of electrons you used- compare it to the number of electrons you have to work with

1) Same Number = Correct Structure2) Need 2 more? Add 1 double bond and change your

dots3) Need 4 more? Add 2 double bonds or 1 triple bond

and change your dots

Intro to Molecular Structures

We spent last week drawing lewis structures of covalent molecules. These are 2D representations of the molecules.

Today we’re going to start talking about the actual 3D structure of the molecules.

Molecular Structure is determined by VSEPR

VSEPR – Valence Shell Electron Pair Repulsion Theory

It means that: Electron pairs (bonds or lone pairs) will get as far apart from each other as they can in 3D space.

This happens because: Electrons are negatively charged and repel each other so they want to stay as far away as possible.

Molecular Shapes

The shape of the molecule depends on the number of and type of electron clouds around the central atom.

Central Atom

Molecular Shape

Electron Cloud: A group of electrons1. Single Bond2. Double Bond (1 double or triple

bond =3. Triple Bond 1 electron cloud)4. Lone pairs

Lone Pairs: The non-bonded electrons that finish the octet. “dots”

There are 5 major shapes

• Tetrahedral• Trigonal Pyramidal• Bent or V-Shaped• Trigonal Planar• Linear

To Find the Molecular shape:

1. Draw the Lewis Structure2. Count the number of bonds (remember

double/triple bond = only 1 bond) on the central atom

3. Count the number of lone pairs on the central atom

4. Match to the correct shape

You need to be able to:

• Match the name of the shape to the lewis structure by being able to identify the electron clouds

• Match the name of the shape to the 3D model

• Know the bond angle of each shape

Tetrahedral

• Four electron clouds• All electron clouds are bonds, no lone

pairs• Bond angle of 109.5°

Trigonal Pyramidal

• Four electron clouds• 3 electron clouds are bonds• 1 electron cloud is a lone pair• Bond angle of 107°- because lone pairs

take up more room

Bent or V-Shaped (Option 1)

• Four electron clouds• 2 electron clouds are bonds• 2 electron clouds are lone pairs• Bond angle of 105°

Trigonal Planar

• Three electron clouds• All 3 electron clouds are bonds• No lone pairs• Bond angle of 120°

Bent or V-Shaped (Option 2)

• Three electron clouds• 2 electron clouds are bonds• 1 electron cloud is a lone pair• Bond angle a little less than 120°

LinearTwo electron clouds both are bonds

OR 1-4 electron clouds- only 1 bonded

Bond angle is 180°

Assignment• Find Covalent Bonds WS 1. For each molecule

answer the following questions:– How many electron clouds are there? How many are

bonds? How many are lone pairs?– Label each lewis structure with the name of the correct

molecular shape– What is the bond angle?

• Covalent Bonds WS 1 is due tomorrow! • When you are done keep working on Covalent

Bonds WS 2 & 3 – this is due tomorrow too!

Giant Molecules – Look at each shape within molecule