10/26/2011
The electrostatic potential maps below correspond to the molecules HNO, FNO, and NO2. Which one is HNO?
Which is the correct Lewis structure for the
nitrate ion, [NO3]– ?
a) b) c)
a) b) c) N
= highly δ+
1
d)
= highly δ–
blue
red
blue = lower χ red = higher χ
χ values: H 2.2, N 3.0, O 3.5, F 4.0
HNO: H has lowest χ, it should appear as blue region compared to red N/O. NO2 and FNO: O and F have higher χ than N, so the N will be slightly blue. O
2
• [NO3]– has 5 + 3x6 + 1 = 24 valence e–
• N has lowest χ so it is central, surrounded by three O
• 24e completes three BP + nine LP on Os
• N requires octet, so one double bond is formed by shifting one O LP to an O‐N BP
What is the formal charge on C atom in the Lewis structure of CO?
Which is the best Lewis structure for nitryl fluoride, FNO2 ? a) –2
b) –1
c) 0
d) +1
e) +2
O
O
a) +2
F
b) N
F
N
O
O
O
c)
F
O
d) N
F
O
CO is highly unusual. It is one of the few stable covalent molecules in which a C atom forms fewer than four bonds. With 5 neighbouring electrons, it carries a –1 formal charge.
3
e)
O
O
4
N
O
a) no octet at N, large FCs
b) satisfies all octets, (–) FC on high χ O, (+) FC on low χ N
c) (+) on highest χ F!
d) exceeds octet at N!
1
10/26/2011
None of the following compounds has lone pairs on the central atom. Which has the largest bond angle?
Which has the shortest O‐O bond length?
Bond
Order
Bond Length
/pm
Bond Energy
/kJmol–1
1
145
142
b) O3
1.5
128
303
c) O2
2
121
495
Lewis structure
a) H2O2
a) BCl3
b) CCl4
c) PCl5
d) SF6
d) they should all be about equal length
5
6
What electron pair arrangement and molecular geometry are predicted for the triiodide anion, [I3]–?
a)
b)
c)
d)
e)
7
What is the most reasonable predicted bond angle for ozone, O3 ?
linear arrangement, linear geometry
trigonal planar arrangement, bent geometry
tetrahedral arrangement, bent geometry
trigonal bipyramidal arrangement, linear geometry
none of the above
3x7 + 1 = 22e
AX2E3 is 5 electron pair regions: trigonal bipyramidal arrangement
3 LPs in the equatorial positions, leaving atoms axial: linear geometry of atoms
No LPs means all AXn structures, with shape determined by expected arrangement of atoms.
trigonal planar: 120°
tetrahedral: 109.5°
trigonal bipyramidal: 120° and 90°
octahedral: 90°
a)
b)
c)
d)
e)
106°
109°
117°
120°
180°
AX2E: a perfect AX3 trigonal planar arrangement would be 120°, but the LP takes up more space and causes greater repulsion than the BP electrons, so the bond angle contracts slightly. 8
2
10/26/2011
Which compound has the smallest molecular dipole?
χ values: Ga 1.81 As 2.18 P 2.19 N 3.04 Cl 3.16
a)
b)
c)
d)
NCl3 μ = 0.6 D
PCl3 μ = 1.0 D
AsCl3 μ = 2.0 D
GaCl3 μ = 0 D
GaCl3 is AX3, trigonal planar with 120° angles. Individual Ga‐Cl bonds are polar, but the bond dipoles cancel, leaving the molecular non‐polar.
9
The other EX3 are pyramidal, and polar. 3