Admin stuff

1
Admin stuff

• OWLs next OWLs due Fri, Mon
• Reading Current Ch. 9
• (skip 9.3)
• Next Ch. 5.1-5.7
• Two handouts today
• Next test Nov. 22 (Tue, 6-730 PM)
• THERE WILL BE NO WEDNESDAY NIGHT MAKE-UP

2
Resonance revisited

• Can diagram the motion of electrons
• Example HCO3

3
The Octet Rule
4
Octet rule exceptions

• BF3, B(OH)3
• reactive (9.9 on CD)

• To few electrons -gt
• incomplete octet

5
What is the best Lewis dot structure of NO?
(Can use formal charge to help make decision)
(1)
(2)
N
O
N
O
N
O
N
O
(4)
(3)
(6)
(5)
N
O
N
O
Odd number of electrons
What are the effects of this?
6
Octet rule exceptions

• NO, NO2 (9.10, 11.9 on CD)

• Free radicals have an odd of electrons
• They have catalytic reactivity
• Free radicals cause biological damage
• NO biologically important

7
PRS

• Draw the Lewis dot structures of SF4 and SF6.
  Which is true for the sulfurs?

• Only the sulfur in SF4 obeys the octet rule
• Only the sulfur in SF6 obeys the octet rule
• Both sulfurs obey the octet rule
• Neither sulfur obeys the octet rule

8
Octet rule exceptions

• Too many electrons
• only happens in 3rd period and below
• Xe compounds
• Reasons

• d-electrons
• atom size
• expanded octets

9
Molecular geometry
10
Peters lone pair predictor

• Count desired electrons on ligands
• ligands are the atoms bound to the central atom
• H atoms want 2 e-, other atoms want 8 e-
• Subtract from total of valence e-
• Gives of unshared electrons on central atom

• Example 1 NH3
• Example 2 NO2
• Example 3 ClF3

How many lone pairs are on the chlorine of
ClF3? (A) 1 (B) 2 (C) 3 (D) 4
(E) 0
11
Peters lone pair predictor

• Count desired electrons on ligands
• ligands are the atoms bound to the central atom
• Subtract from total of valence e-
• Gives of unshared electrons on central atom

• Example 1 NH3 has 8 e-, ligands want 6 e-
• Left with 2 e- on central N (one lone pair)
• Example 2 NO2 has 17 e-, ligands want 16 e-
• Left with 1 e- on central N (1/2 of a lone pair)
• Example 3 ClF3 has 28 e-, ligands want 24 e-
• Left with 4 e- on central Cl (two lone pairs)

12
Octet rule exceptions

• Too many electrons
• only happens in 3rd period and below
• Xe compounds
• Reasons

• d-electrons
• atom size
• expanded octets

13
Polyatomic ions revisited (SO42-, H3PO4)

• Which is the best structure for the SO42- ion?

(A)
(C)
O
O
S
O
O
S
O
O
O
O
O
S
O
O
O
(B)
14
Octet rule exceptions

• d-electrons are involved configurations?

15
The five electron pair geometries

• The number of electron pair sites on the central
  atom plays a key role in determining molecular
  shape
• How do we count electron pair sites?
• Each lone pair counts as an electron pair site
• Each bonded atom counts as an electron pair site
• (Note that a triple does NOT count more than a
  single bond)
• Each unpaired electron (radical) counts as an
  electron pair site

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3
4
5
6