Resonance

1. Resonance • There are certain cases in which a single Lewis structure cannot correctly describe a molecule. • Example: O3 • Experimental evidence shows each of the oxygen-oxygen bonds are identical. • Actual structure is an average of the resonance structures.

2. Polyatomic Ions • Group of covalently bonded atoms that has a charge. (a charged molecule) • Example: NO3- (nitrate ion)

3. Polar and Nonpolar Covalent Bonds • Covalent bonding involves sharing electrons between atoms. • Nonpolar covalent bond – equal sharing of electrons between two atoms. • Both atoms have same attraction for shared pair. • Example: H – H

4. Polar covalent bond– unequal sharing of electrons between atoms. • One atom has greater attraction for shared pair. (Tug – of – War) • Example: H – Cl • This creates partial (d) charges on each atom in the bond.

5. The atom that has a greater attractionfor shared electrons takes on a partialnegativecharge. The atom with a weaker attractiontakes on a partial positivecharge. • How can you determine which atom has greater attraction for electrons? • ELECTRONEGATIVITY

6. Can use the difference in electronegativities between two atoms to predict the type of bond formed between the atoms.

7. Sample Problem: • Use electronegativities to determine the type of bond that will form. If the bond is polar, decide which atom is partially negative and which is slightly positive. (a) C and S (b) Na and O (c) P and Cl