WarmupP-H N-H F-H

a. Use your EN chart to calculate the EN differences of the bonds shown above

b. Rank the bonds in order of decreasing polarity (most polar to least polar):

c. Draw the distribution of the electron cloud around each bond and the dipoles

Lewis Structures*refer to handout on the back of the

Molecular Modeling Activity

https://www.youtube.com/watch?v=NgD9yHSJ29I

Bonding (Shared) Pair

Bonding (Shared) Pair

Lone (Unshared) Pair

Lone (Unshared)

Pair

Atoms in a covalent bond share valence e- to achieve completely satisfied valence shells.Lewis structures are drawings that show HOW

atoms are covalently bonded.

Ex. Draw the Lewis Structure for ICl

Hmmmmm how many val e- does iodine have?

What about chlorine?

I

I Cl

ClI

I Cl

I Cl

I Cl

I Cl

I Cl

*They each share 1 e- with each other

How many val e- does each atom have?

I Cl 8 Valence electrons

8 Valence electrons

Both end with “full octets”. All elements MUST end up with a full octet (few exceptions)

C =(4 e-)(1 atom) = 4(1 e-)(2 atoms) = 2

H =

12 valence e-

Ex. Draw the Lewis Structure for H2CO1) Calculate total # of valence e-

O = (6 e-)(1 atom) = 6

What about harder structures? Let’s try like…..a method…

2) Plan the molecular skeletonHints: C is often central, H and halogens are never central, O is rarely central

Draw the Lewis Structure for H2CO

3) Place 1 pair e- between each of the atoms

4&5) Add in e- to create double/triple bond or

lone pairs so that:

6) Check that each atom is surrounded by 8 valence e- and that total valance e- are all used

C OH

H

6 val e-

7. Final structure: replace each bonding e- pairs with a line

H

HC = O

Clarification: the structural formula shows bonds as lines and the lone pairs aren’t ALWAYS included. A dot diagram represents bonding electrons pairs as dots. A Lewis structure can technically be either, we are not too particular.

Simple Structures Practice

CH4

HF

H2

H2O

HF and H2O are polar

molecules (uneven

distribution of electrons)

More Practice

CH3Br

NH3

SF6

BCl3

WEIRDNESS!!!!

expanded octetSulfur usually makes 2 bonds but can

make up to 6 H

S

H

H2S

SF F

F F

F F

SF6

Phosphorus can also expand it’s octet. Nitrogen cannot.

Incomplete Octet

BCl3 BeF2 B

Cl

Cl

Cl

Violation

Be FF

Violation

on

More Practice OH-

Total e-

6 + 1 + 1

NH4+

Total e-

5 + 4 – 1

N2

10 e- total, but

double or

triple bond?

H O [ ]-1

Some orbitals are full and don’t have to

overlap (lone pairs!)CCOO OO

A bond is not ACTUALLY 2 dots (or 4 or 6) in between two atoms!!!!!!!!!!!!!!!!!!!!

A bond is formed when one orbital (containing an electron) overlaps with an orbital from another atom. The electrons are shared and travel within the two orbitals….they are SHARED.

2e-

2e-

1e-

1e-1e-

1e-

1e-1e-

You will not need to draw

something like this!!!