Ch1 a

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