Bonding Types – ionic and covalent
Covalent Bonding – equal/unequal sharing
Bonding Model – Lewis Structures (with formal charge and resonance structures)
How compounds are held together: covalent vs ionic bonding
Electronegativity:measure of attraction for electrons in a bond
0 0.4 1.9
Nonpolar
Very slightly polar(called nonpolar)
Polar
No sharing(Ionic bond)
Electronegativity Difference
DEN and Bond Polarity Scale
Electronegativity Trends
Bond vs Molecular Polarity
Lewis Structures: model to describe bonding in covalent molecules
- Valence electrons represented by dots- Bonding pair represented by line- Valence e- so 2 for H and 8 for 2nd row elements
Formal Charge: way of keeping track* of where charge is within a molecule
FC = group number – nonbonding e- – ½ shared e-
Electrons that contribute to atom’s charge:1. All of unshared electrons2. Half of shared electrons
Resonance (when 1 Lewis structure doesn’t tell the story well)
Resonance “rules of thumb”
• Must be valid Lewis structure• Move electrons, not nuclei• Number of unpaired electrons (if any) remain
the same• Major contributor has lowest energy (see
other rules)• Resonance – most important when charge is
delocalized
Comparing Resonance Structures
• As many octets as possible• As many bonds as possible• Any negative charges on electronegative
atoms• As little charge separation as possible
Common Bonding Patterns