Chapter 8 Second set of Chapt. 8 homework dates extended until after break Lab Notes Today’s Topic: Bond Properties (Sec there is no 8.3!) Electron Distribution in Molecules (8.5) November 16, 2009

What can we do with Lewis Structures? Bond Properties 1. Polarity 2. Bond Order 3. Bond Length 4. Bond Energy

Bond Energy= The energy required to separate two bonded atoms Remember- It ALWAYS takes energy to break a bond! Making bonds releases energy.

It ALWAYS requires energy to BREAK a bond! The phosphate bond in ATP is not “broken”, it is hydrolyzed, a multi- faceted process that does result in a net release of energy. However, it involves more than the simple breaking of one bond.

Bond Energy in Ionic Compounds: Lattice Energy Energy to separate all the ions NaCl(s)  Na + (g) + Cl - (g)  H = Lattice E = -790 kJ/mol

Lattice Energy Lattice energy = the energy it takes to pull ions in a solid apart  Remember Coulomb’s Law!  Depends on ion SIZE  Depends on ion CHARGE

Which has the strongest lattice energy? 1. MgCl 2. BaCl 3. KCl 4. CsCl

Internal Properties of Molecules Resonance Formal Charge Oxidation Number Partial Charge

Resonance Structures A resonance structure is when more than one arrangement of electrons is possible (i.e., there is more than one reasonable Lewis structure)

Resonance and Bond Order Bond order will not equal the # of bonds if there is more than one possible structure What is the bond order of the C-O bond in the carbonate ion?

What is the bond order in SO 2 ?