Exceptions to Octet Rule Lewis Structures & Stability Multiple Bonds Bond Energies Resonance Exceptions to Octet Rule

Stability and Bond Energies Bond energy is a measure of stability. Bond energy – amount of energy required to break a bond holding two atoms together. The values of bond energies decrease in order: triple > double > single. Example: N2 > O2 > H2

Bond Length Bond length – distance of separation of the bonded nuclei Bond length is related to the presence or absence of multiple bonding. Bond length decreases as the number of bonds increase: single > double > triple

Resonance In some cases, it is possible to write more than one Lewis structure that satisfies the octet rule. Experimental evidence shows no double bond exists. The actual structure is a hybrid of these two.

Draw the resonance structures for: Practice - Resonance Draw the resonance structures for: Ozone (O3) Benzene (C6H6)

Ozone

Benzene

Exceptions to the Octet Incomplete octet Example: BeH2 Applies only to B and Be Odd electron molecules Example: NO Expanded octet Example: PF5 Applies to non-metals in periods 3-7 These elements have empty d-orbitals for excited electrons to jump into, creating more bonding sites

Homework Pages 99 and 101 Problem #’s 4.17 – 4.20