exam style q's-answers

chapter 3--bonding

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AS Chemistry Chapter 3
Extension
Answers to teacher notes questions
examination-style
Answers Marks Examiner's tips
1 (a) F ­ 2 These shapes do not have lone pairs so
F
B F don't try and put them in.
F F B F
F 1
BF3 trigonal planar 1 BF4­ is a regular tetrahedron.
BF4­ tetrahedral 1 Learn the angle in a tetrahedron is 109°
1 or 109.5°
equal repulsion between 4 bonding pairs
109(½)°
(b) lone pair donated by one atom 1
from F­ to B 1
ative or dative covalent or co-ordinate
d 1
bonding
2 m
acromolecular means a giant molecule with 1
covalent bonding
he white P has van der Waals forces between
t 1 If you mention the wrong type of
the P4 molecules intermolecular force you will lose marks.
and these forces are weak 1
he red phosphorus has many covalent bonds
t 1 The covalent bonds are broken on
that must be broken melting, not just loosened or weakened.
and covalent bonds are strong 1
3 (a) electronegativity is the power of an atom to 1
attract electron density or the bonding pair
of electrons
in a covalent bond 1 Learn this definition.
(b) (i) F2 = van der Waals forces 1
CH3F = dipole­dipole forces 1 Don't just say `dipole'.
HF = hydrogen bonding 1 Don't just write just `H' or `hydrogen'.
(ii) l
arge difference in electronegativity 1
between H and F
+
H­F­dipole created 1
ttraction between +H and lone pair
a 1 This may be shown on a diagram. Put in
on F partial charges () not full charges.
AQA Chemistry AS Level © Nelson Thornes Ltd 2008

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AS Chemistry Chapter 3
Extension
Answers to teacher notes questions
examination-style
Answers Marks Examiner's tips
(c) (i) van der Waals forces 1
ncrease with the increasing
i 1
molecular size / mass of the hydrogen
halides
(ii) h
ydrogen bonding stronger than van 1 Put the comparison in. Don't just talk
der Waals forces about one substance.
4 (a) oxygen more electronegative (than hydrogen) 1 Don't mention covalent bonds. Just talk
about intermolecular forces and compare
causes H+­O­ 1 their strengths.…read more

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AS Chemistry Chapter 3
Extension
Answers to teacher notes questions
examination-style
Answers Marks Examiner's tips
6 (a) SF6 shape is octahedral 1 Make sure you include the symbols for
bond angle = 90° 1 the elements in the diagram.
shape = 1
F
F F
S
F F
F
equal repulsion between 6 bonding pairs
1
of electrons
AlCl4­ shape is tetrahedral 1
bond angle = 109° to 109.…read more

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AS Chemistry Chapter 3
Extension
Answers to teacher notes questions
examination-style
Answers Marks Examiner's tips
(c) (i) 90° 1
(ii) l
one pairs repel more than bonding 1
pairs
so are as far apart as possible 1
(iii) square or square planar 1
(d) 2
N
F F
F
8 (a) (i) positive ions 1 Don't get confused with negative ions or
attract delocalised electrons
1 ionic lattices.…read more

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