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!!!