2.2.11-2.2.12 - Resonance Structures and Benzene
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When are resonance structures relavent?
when there are multiple locations within a molecule that a double bond could be
What is an example of a molecule that needs resonance structures?
NO3-
What is different about the bonds with resonance structurs than typical?
all 3 (in the case of NH3-) are the same length and strength - greater than a single bond but weaker than a double bond
What is going on with the electrons in the double bond with resonance structures?
they are not localized to one bonding location but are spread out over a region, in a cloud
what is a resonance structure drawn?
same as lewis structure but with dotted lines showing where possible double bonds are/ showing that the extra double bond is across all bonding sites
What is the relation between bond order, electron density, bond strength and bond length?
the higher the bond order, the greater the electron density and stronger and shorter the bond length is
What is the formula for bond order?
Bond order = # shared electron pairs/# of bonding positions
What is the bond order of single bonds?
1
What is the bond order of double bonds?
2
What are conjugated systems?
alternating double and single bonds
What is the formula for Benzene?
C6H6
How is benzene drawn?
hexagonal shape, alternating double and single bonds
What are the evidence for delocalized electrons in benzene?
no isomers, unsaturated, does not readily undergo addition reactions, bond enthalpy does not reflect single or double bonds
What are some special properties of delocalized electrons?
greater stability, resonance energy, electrical conductivity
Why does delocalized electrons mean greater stability?
delocalization allows electrons to spread out and reduces repulsion
What is resonance energy?
extra energy required to get molecules with delocalized electrons to react
How do delocalized electrons allow for electrical conductivity?
the electrons move across the structure in response to voltage (allows electrical conductivity in solid state)