Lewis Structure Activity
Valence Electrons:


Electrons on farthest energy level of the atom
Based off the group number they are in
o Transition metals all have 2 valence electrons due to the s-orbital having a higher
energy level
How do you identify the energy for an atom?
Octet Rule:


Atoms with 8 valence electrons are the most stable version of an atom
o Exceptions are:
 H/He = 2 total valence electrons
 B = 6 total valence electrons
Noble gases don’t react because of the full octet
o Atoms will gain/lose/share valence electrons in order to achieve a full octet, this is
done through bonding
Types of Bonds:


Ionic Bonds: electrostatic attraction between a metal cation (low ionization energy) and a
nonmetal anion (high electronegativity) due to transfer of valence electrons
Covalent Bond: two or more non-metals sharing electrons due to their electronegativity values
being close, both atoms want an electron and therefore they will share
Valence electron count
Li
Al
C
Cl
Kr
O
N
How much is gained or lost
Lewis Structures:

3D structures that show how each atom shares their valence electrons
What type of compound are we working with then and how did you know that?
Steps to drawing a Lewis Structure
1. Identify the total number of valence electrons in the compound
2. Place the unique atom (the atom with the fewest in the compound) – usually carbon – in the
middle  Central Atom
3. Surround the central atom with remaining atoms from the compound
a. Place a ‘-‘ between the outside atom and the central atom. This represents a bond and a
bond is made up of 2 electrons
4. Count up bonded electrons, if it does not equal the total original valence electron count, add
remaining electrons as lone pairs as needed
a. Every atom needs an octet – achieved either through bonding or lone electron pairs.
Remember your exception (H: 2 therefore can only make 1 bond)!!!!
C – 4 ve
H – 1 ve x 4
Total = 8 ve
Central atom (only
atom
Lone pair of electrons
to complete octet
N – 5 ve
H – 1 ve x 3
Total = 8 ve
4 bonds = 8 ve
3 bonds = 6 ve
1 lone pair = 2 ve
Total= 8ve
present)
Bond – represents
2 electrons
Remaining atoms
placed around
central atom
Multiple Bonds:
Compounds will make multiple bonds (2 = double, 3 = triple) if there are not enough
valence electrons available to complete the octets.
C – 4 ve
H – 1 ve x 2
O – 6 ve
Total = 12 ve
4 bonds = 8 ve
2 lone pair = 4 ve
Total= 12 ve
X
X
If carbon is present it
will always be the
central atom
X
X
Lone electron pair
on oxygen to
complete octet
Carbon always has 4
bonds – never lone
pair of electrons
Practice:
H2O
HF
PF3
SiO2
SO2
CH2Br2