Chemistry for Engineers

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Chemistry for Engineers Homework 2 B O N D I
N G Answer Key
Electron arrangements
2
Q1 Fill in every blank box regarding the atoms
or ions of the following isotopes
3
Q2 The Lewis structures for the following ions
are almost complete. They show the bonding pairs
and lone pairs but charges on atoms are not
shown. Redraw each and add charges to atoms that
need them.
a) H3O
d) OH-
b) NCS-
e) N3-
c) HCO
4
Q3 For each molecule a) How many valence
electrons are there? b) Draw out the Lewis
structure c) Deduce the oxidation state of the
central atom d) Indicate bond polarity using d
and d- symbols and overall molecule polarity with
ClF SF2 PH2Br HCOOH
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ClF SF2 PH2Br HCOOH
ClF
Count up valence electrons 14 Count up
valence electron pairs 7 Determine which
atoms are bond to which (struc. formula)
Cl?F Form single bonds between neighbouring
atoms (6 electron pairs remain
unused) Use remaining electron pairs to complete
octets of each atom (three lone pairs on each
halogen atom)
c) Cl oxidation state is 1
d-
d
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SF2 Count up valence electrons
20 Count up valence electron pairs
10 Determine structural formula Form single
bonds between neighbouring atoms (8
electron pairs remain unused) Use remaining
electron pairs to complete octets of each
atom (F octet must be completed first) leaves
two lone pairs on S
ClF SF2 PH2Br HCOOH
d
d-
c) S oxidation state is 2
d-
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PBrH2 Count up valence electrons 14 Count
up valence electron pairs 7 Determine
structural formula Form single bonds between
neighbouring atoms (4 electron pairs
remain unused) Use remaining electron pairs to
complete octets of each atom (Br octet must be
completed first) leaves one lone pair on P
ClF SF2 PH2Br HCOOH
d
d-
c) P oxidation state is 1
8
HCOOH Count up valence electrons
18 Count up valence electron pairs
9 Determine structural formula Place C at
centre and form single bonds between
neighbouring atoms (5 electron pairs remain
unused) Use remaining electron pairs to complete
octets of each electronegative atom BUT
- not enough electrons to complete carbons
octet so CO double bond must form by donating O
lone pair
ClF SF2 PH2Br HCOOH
C has incomplete octet!
d-
d
d-
c) C oxidation state is 2
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Q4 Consider the sulphite anion (SO32-). a) How
many valence electron pairs are there? Draw the
Lewis resonance structures of the anion. valence
electrons 26 (13 pairs) place S as central atom
and use 3 pairs single bonds S can expand
valency so double bond can be drawn now move p
bond to illustrate resonance structures
(S has 6 valence electrons so retains a lone pair)
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b) What is the charge on each oxygen atom? -
0.667 (two thirds of a negative charge) c) Given
that the strength of a typical S-O single bond is
360 kJ/mol, estimate the S-O bond strength in the
sulphite ion. bond order 1.33 bond strength
expected 480 kJ/mol.
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Q5 For the following species I2 IF4
IF3 PI3 a) Deduce the
oxidation state of iodine b) How many valence
electron pairs are there? c) Draw the Lewis
structure d) What is the geometry of the
electron pairs (e.g. linear, trigonal
bipyramidal etc)? What are the bond angles and
molecule shape? e) What related anion has I in
the 1 oxidation state?
IF2-
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Q5
I2 IF4 IF3 PI3
iodine oxidation state 0 5
3 -1 valence electrons 14
34 28 26 valence electron pairs
7 17 14 13
F-I-F 90º F-I-F 90º I-P-I
102º 120º
trigonal bipyramid (molecule is T-shaped)
distorted tetrahedral (molecule is pyramidal)
trigonal bipyramid (atoms arranged as sawhorse)