Practice: PRACTICE: Analyze the following molecules. Indicate ALL atoms that are in violation of the octet rule.
This might be the most important rule in all of undergraduate chemistry! Let’s start from the beginning and go from there.
Noble Gas Configuration
Concept #1: How Noble gases are related to the octet rule.
The tendency for atoms to share electrons to reach their Noble gas configuration is known as the Octet Rule.
LCAO of Noble Gases
Concept #2: LCAO model proves why Noble gases are so stable.
The LCAO of He2
Science-y Version: Helium would have to fill an anti-bonding molecular orbital in order to bond to itself, which undoes the extra stability provided by the filled bonding orbital, so it has no reason to make a bond.
Basic Version: Noble gases don’t like to bond to anything!
Periodic Table Patterns
Concept #3: The most important parts of the periodic table for organic chemistry.
- Only worry about the elements on the first 2 or 3 rows. Living systems don’t have a lot of heavy metals!
- Periods = Rows, Groups = Columns.
- Remember your Group 1A through 8A elements. We will practice memorizing the top atom of each group.
Octet Rule Details
Concept #4: The octet rule.
- First-row elements (H, He, Li) will prefer to possess 2 octet electrons
- Second-row elements (C, N, O, F) will prefer to possess 8 octet electrons
- Atoms smaller than carbon will possess less than 8 electrons: (Be) = 4 and (B) = 6
- Third-row elements may form expanded octets that can hold up to (P) = 10 and (S) = 12 electrons.
Octet electrons is the name we give to ALL electrons that surround an atom. These help the atom reach its Noble gas configuration.
- Bonds = 2 Octet Electrons
- Lone Pairs = 2 Octet Electrons
It seems like a lot to memorize, so let’s just knock out some practice problems.
From now on let’s just agree that hydrogens with 1 bond and carbons with 4 bonds follow the octet rule, instead of multiplying them out every time.
Practice: PRACTICE: Analyze the following molecules. Indicate ALL atoms that are in violation of the octet rule.
You’ll keep seeing the octet rule a bunch more in this chapter. Let’s move on.
