chapter 2: bonding fundamentals (lewis structures & formal charge)

Why is bonding best thought of as a spectrum?

Bonding ranges from ionic (Δ𝐸𝑁 > 1.7-2.0) → polar covalent (Δ𝐸𝑁 = 0.4-1.7) → nonpolar covalent (Δ𝐸𝑁<0.4) depending on electronegativity difference. Most organic bonds are polar covalent, not fully ionic.

What do Lewis structures tell us (and not tell us)?

Lewis structures show:

• connectivity

• number of bonds

• lone pairs

• formal charges

They do not show 3D geometry or orbital hybridization.

What is the formal charge formula?

Formal charge = (group number) − (nonbonding electrons) − ½(bonding electrons)

Formal charge helps compare Lewis structures and predict stability.

How do you determine the most stable Lewis structure?

Stability rules (in order):

1. Full octets (exceptions: H, some cations)

2. Fewest formal charges

3. Negative charge on most electronegative atom

4. Expanded octets allowed for period ≥3 atoms