Chem 105 – Fall 2009 ‐ Keller Review sheet for Hour Exam 4 Covers Ch. 8 (Bonding and Molecular Structure) and Ch. 9 (Molecular Orbital Theory). The format of exam 4 will be similar to the others we have had: 16 multiple choice questions, followed by several short answer questions totaling 20 points. The former are scanner‐graded. The latter are hand‐graded by JK or a teaching assistant. There are certain facts and ideas that you will need to bring with you (mentally) for this exam. I will make a concise list of these here on one page. This is not exhaustive, but it does hit some of the high points. Ch. 8 (Bonding and Molecular Structure) Examples
Count up valence electrons for atoms, molecules, and ions (no C atom = 4 (the group number) transition metals) Cl‐ ion = 8 (group number + 1 extra) NOCl = 5 + 6 + 7 = 18 BrO3‐ = 7 + 3(6) + 1=26 Using the Octet Rule, draw Lewis structures for molecules and ions with C, N, O, Si, P, S, Cl as central atom N
O Br O
O
Draw Lewis structures for molecules that contain central atoms with fewer (Be and B) or more than (P, S, Cl, As, Se, Br, I, Xe) an octet. Write resonance structures in cases where different (reasonable) Lewis structures are possible. Use VSEPR theory to predict the shapes of molecules & ions.
Remember the five electron pair, or “no‐lone‐pair” molecular, geometries. Remember the “lone‐pair‐containing” molecular geometries.
Remember the general trends for electronegativity of atoms
Predict the polarity of molecules using geometry and relative electronegativity. Identify µ = 0.00 D due to high symmetry, or predict differences in µ. Calculate ΔH using table of bond dissociation energies, or vice versa Ch. 9 (Molecular Orbital Theory) Identify the hybridization of an atom in a molecule, which is based on the number of bonds (single or multiple) + lone pairs originating at the atom. Remember the electron pair geometry associated with ea hybridization Understand original, shapes, and numbers of σ and π bonds
Assign electrons for diatomic molecules and ions to an MO diagram following Pauli Exclusion Principle and Hund's Rule. Predict the bond order and magnetic properties based on same Cl
O
F
Cl
Be Cl
F
O
O N
F
S
F
O
F
O N
O
F
O N
F
BeCl2 is linear; SF4 is see‐saw. Linear; trigonal planar; tetrahedral; trigonal bipyramidal; octahedral. Bent; trigonal pyramidal; see‐saw; tee‐shaped; linear; square pyramidal; square planar. Incr across row to rt; Incr up a group. F high
µ = 0.00 D for BeCl2. µ (CH2F2) > µ (CH2Cl2) (2.46 vs. 2.04 D) ΔHr = ΣΔH(bonds broken) ‐ ΣΔH(bonds formed)
sp, sp2, sp3, sp3d, sp3d2 (2, 3, 4, 5, 6 respectively)
Linear; trigonal planar; tetrahedral; trigonal bipyramidal; octahedral σ
O
π
phosgene
Cl
C
(COCl2)
Cl
Cl
Cl
BO = ½ (electrons in bond MOs ‐ electrons in anti‐bond MOs) e.g. the peroxide ion O22‐ has a bond order = 1= ½ (10‐8)