Warmup P-HN-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

Bonding (Shared) 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

I

I

I

I

I

I *They each share 1 e- with each other

l How many val e- does each atom have? ICl 8 Valence electrons l 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 H 2 CO 1) 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 skeleton Hints: C is often central, H and halogens are never central, O is rarely central Draw the Lewis Structure for H 2 CO 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 O H H 6 val e-

7. Final structure: replace each bonding e- pairs with a line H H C= 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 CH 4 HF H 2 H 2 O HF and H 2 O are polar molecules (uneven distribution of electrons)

More Practice CH 3 Br NH 3 SF 6 BCl 3 WEIRDNESS!!!!

expanded octet Sulfur usually makes 2 bonds but can make up to 6 Phosphorus can also expand it’s octet. Nitrogen cannot.

Incomplete Octet BCl 3 BeF 2 on

More Practice OH - Total e NH 4 + Total e – 1 N2N2 10 e- total, but double or triple bond? H O [ ] -1

Some orbitals are full and don’t have to overlap (lone pairs!) COO 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- 1e- You will not need to draw something like this!!!