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Answers to problem sheet 6 in the chem1901/3 course, focusing on molecular structures and bonding. It covers various organic and inorganic compounds, including their lewis structures, bond orders, and resonance structures. Additionally, it introduces the concept of vsepr theory and its application in predicting molecular shapes.
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CHEM19 01 /3 Answers to Problem Sheet 6
H C N Bond order = 3 (triple bond)
(b) ethanol, CH
3
2
Two lone pairs on oxygen.
(c) pyridine, C 5
5
Pyridine has delocalized ‘aromatic’ electrons like benzene with a lone pair on
nitrogen instead of a C-H bond. Note that this lone pair is pointing away from the
ring and is not delocalized.
(d) acetylene, C
2
2
(e) SOCl 2
Cl S Cl
Cl S Cl
The resonance structure on the left shows the (allowed) expanded valence shell
around S with 5 electron pairs (4 bonds for the S(IV) atom and 1 lone pair). The
resonance structure on the right shows all atoms obeying the octet rule leading to
charges having to be placed on S and O.
(f) N 2
4
Each resonance form is equivalent – the N-O bonds are intermediate between single
and double bonds in character. There is no multiple bond between the nitrogen atoms.
N N
O O
O O
N N
O O
O O
N N
O
O
O
O
N N
O
O
O
O
(g) phosphoric acid,
3
4
3
The resonance structure on the left shows the bonding with an expanded valence
shell around P (five bonds for the P(V) atom). The resonance structure on the right
shows all atoms obeying the octet rule but with charges.
(h) phosphate anion,
4
3 –
The resonance structures all feature one double P=O and three single P-O bonds.
Overall, each P-O bond is equivalent with:
bond order = ¼ (3 × 1 (single)+ 1 × 2 (double)) = 1.
(i) methylsulfate anion,
3
3
(f) SF 4
trigonal
bipyramid
see-saw
(g) ClF 3
F Cl F
trigonal
bipyramid
T-shaped
(h) XeF 2
F Xe F
trigonal
bipyramid
linear
(a) (b) (c)
3
3
3
(d) (e) (f)
3
3
3
3
3
3
3