View
245
Download
0
Category
Preview:
Citation preview
8/17/2019 Chemical Bonding Revision (ANSWERS)
1/31
Name: Date:
Chemical Bonding
Qn 1 Electric cable, as used in houses, is made of copper wire surrounded by
poly(chloroethene), also called polyvinylchloride or PVC.
(a) (i) Describe the bonding in copper and eplain how it conducts electricity.
definition of metallic bonds
Copper has strong electrostatic forces of attractions between a
giant metallic lattice structure of cations/Cu2+ and sea of electrons.
Copper contains mobile electrons to conduct electricity.
(ii) Describe the bonding in PVC and hence eplain why it acts as an
insulator.
definition of covalent bonds
PVC is polyvinyl chloride, a polymer with molecular structure with
strong electrostatic forces of attraction between shared pair of
electrons and nuclei
PVC does not contain mobile ions or electrons to conduct electricity.
(b) !owever, electric cable used in fire alarm systems has copper wire
surrounded by magnesium oide which acts as an insulator. "he whole
cable is encased in thin copper tubing.
(i) Describe the bonding in magnesium oide and eplain why it acts
as an insulator.
Page 1 of 31
Describe:
Give definition
of bonds,
not just the name
8/17/2019 Chemical Bonding Revision (ANSWERS)
2/31
definition of ionic bonds
Strong electrostatic forces of attraction between oppositely
charged #g $% and &$' ions.
ons can only vibrate about fixed position and hence are not mobile
to conduct electricity.
(ii) uggest two reasons why magnesium oide is preferred to PVC
as an insulator.
• g! will not "urn to produce toxic gases
• g! has higher melting point to withstand high temperature in
event of fire.
(iii) uggest a reason why copper is suitable for encasing the
magnesium oide.
Copper is
• High tensile strength provides support for brittle g!
#"ecause g! is giant ionic$
• !r "esistant to corrosion
Note: %ensile strength is the resistance of a material to tear apart,
measured as the ma&imum tension the material can withstand.
Qn # (a ) *oron trifluoride, *+ and aluminium fluoride, -l + differ maredly in their
physical properties.
Compound Melting point / °C
*+ '/00 -l + /$1/
Deduce the type of bonding present in each of these compounds and draw
dot and cross diagrams to illustrate this bonding.
$ow melting point indicates '() e&ist as simple molecular structure with
Page # of 31
Deduce/Predict: need to give reason with inference from the given data
Analysis: Formula suggested AlF3 and BF
3 should have similar type of structure.
But, melting point differ actual type of structure actual type of bonding
Answer to include: structure and type of intramolecular bonding
8/17/2019 Chemical Bonding Revision (ANSWERS)
3/31
covalent bonds "etween ' and ( atoms
High melting point indicates *l() e&ist as giant ionic structure with
ionic bonds "etween oppositely charged *l)+ and ( ions
3+ -
Al 3 F
a) *oron trifluoride forms a compound with ammonia. Describe the type of bond
that is formed during this reaction. Draw a diagram to illustrate the shape and
bonding in the product.
% atom in N) donates the lone pair of electrons to B with vacant
orbital/incomplete octet forming a co&ordinate (or dative covalent) bond.
Shapes and Polarity
Qn 3 Draw the dot'and'cross diagram and 2ewis structure (if applicable) for each
substance and hence eplain the following observations3
(a) C&$ and ICl 2' are both linear, but have different number of electron pairs
(a) C!#
• %here are # bond pairs and ' lone pair around C
• %o minimise repulsion, the # electron pairs are directed to opposite
sides of each other
Page 3 of 31
B FF F
C !!(
(
(
(
C! !
*l forms ionic compounds with
* ! and %-
"ut covalent compounds with
other nonmetals, eg. Cl, 'r, I
8/17/2019 Chemical Bonding Revision (ANSWERS)
4/31
• C!2 is linear
ICl #&
I xx
xx
x
x&
Cl
Cl
I
Cl
Cl
• %here are # bond pairs and 3 lone pairs around I
• %o minimise repulsion, the + electron pairs are directed to the corners of
a trigonal bip,ramid• -ince lone pair & lone pair repulsion . lone pair bond pair repulsion
. bond pair&bond pair repulsion
• ICl2 is also linear
Qn 3 Draw the dot'and'cross diagram and 2ewis structure for each substance and
hence eplain the following observations3
(b) &2 and C l $ are both bent, but show different bond angles.
(b) -!#
(((
(
(
(
.! !
.! !
• %here are # bond pairs and 1 lone pair around
• %o minimise repulsion, the 3 electron pairs are directed to the corners of
an e0uilateral triangle
• -ince lone pair & bond pair repulsion . bond pair&bond pair repulsion
• !2 is bent with "ond angle of 1#''C.
Page 2 of 31
Lone pair should be
represented by dots
(eatures of linear shape
# bond pairs as indicated "y the # neighbouring atoms
num"er of lone pairs is either ' or 3.
http://sg.wrs.yahoo.com/_ylt=A0S0zvjR551J_nQAi1gl4gt.;_ylu=X3oDMTBpdnJhMHUzBHBvcwMxBHNlYwNzcgR2dGlkAw--/SIG=1kumfqjbd/EXP=1235171665/**http%3A/sg.images.search.yahoo.com/images/view%3Fback=http%253A%252F%252Fsg.images.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimage%2526ni%253D18%2526va%253Dbulb%2526fr%253Dyfp-t-web%2526xargs%253D0%2526pstart%253D1%2526b%253D1%26w=253%26h=270%26imgurl=www.istockphoto.com%252Ffile_thumbview_approve%252F184350%252F2%252Fistockphoto_184350_light_bulb.jpg%26rurl=http%253A%252F%252Fwww.eastchester.k12.ny.us%252Fschools%252Fhs%252Fteachers%252Fgorycki%252FBiologySites.htm%26size=9kB%26name=istockphoto_184350_light_bulb.jpg%26p=bulb%26type=JPG%26oid=8d8c8d8c0312810e%26no=1%26tt=1299987%26sigr=12dnc7j6u%26sigi=12ltb8o27%26sigb=13f3ckjbb
8/17/2019 Chemical Bonding Revision (ANSWERS)
5/31
-Cl #
x x.Cl Cl
x
x
x
x x
xx
xx
xxx
x
.
Cl Cl
• %here are # bond pairs and # lone pairs around
• %o minimise repulsion, the 2 electron pairs are directed to the corners of
a tetrahedron
• -ince lone pair lone pair repulsion . lone pair & bond pair repulsion
. bond pair&bond pair repulsion
• -Cl # is bent with "ond angle of 1'2+'C
Qn 3 Draw the dot'and'cross diagram and 2ewis structure for each substance and
hence eplain the following observations3
(c) 4&' and & are both trigonal planar, but show different bond types.
(b) %!3&
&
!! &&& &&
&&
&&
! &&
&&
&&
&
N
N
!!
-!
-!3
Page + of 31
(eatures of bent or non&linear shape
# bond pairs as indicated "y the # neighbouring atoms
num"er of lone pairs is either 1 or #
bond angle4 # lone pairs (1'2+') 1 lone pair (1#'')
due to additional lone pair&lone pair repulsion
Charge of &1 add / electron to more electronegative !
such that / ! atom has 0electrons
form a single bond
http://sg.wrs.yahoo.com/_ylt=A0S0zvjR551J_nQAi1gl4gt.;_ylu=X3oDMTBpdnJhMHUzBHBvcwMxBHNlYwNzcgR2dGlkAw--/SIG=1kumfqjbd/EXP=1235171665/**http%3A/sg.images.search.yahoo.com/images/view%3Fback=http%253A%252F%252Fsg.images.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimage%2526ni%253D18%2526va%253Dbulb%2526fr%253Dyfp-t-web%2526xargs%253D0%2526pstart%253D1%2526b%253D1%26w=253%26h=270%26imgurl=www.istockphoto.com%252Ffile_thumbview_approve%252F184350%252F2%252Fistockphoto_184350_light_bulb.jpg%26rurl=http%253A%252F%252Fwww.eastchester.k12.ny.us%252Fschools%252Fhs%252Fteachers%252Fgorycki%252FBiologySites.htm%26size=9kB%26name=istockphoto_184350_light_bulb.jpg%26p=bulb%26type=JPG%26oid=8d8c8d8c0312810e%26no=1%26tt=1299987%26sigr=12dnc7j6u%26sigi=12ltb8o27%26sigb=13f3ckjbb
8/17/2019 Chemical Bonding Revision (ANSWERS)
6/31
. &
&
&
!! &&& &&
&&
&&
&&&
&&
& &
! &
.
! !
!
• 'oth have 3 bond pairs and ' lone pair around N and respectively
• %o minimise repulsion, the 3 electron pairs are directed to the corners
of a trigonal p,ramid
• 'oth are trigonal planar
• N, "eing an element in period #, has no d orbitals in valence shell
#n12$ to accommodate electrons and cannot expand "eyond octet
structure ence, dative bond is formed instead of double bond.
5eriod 3 onwards elements 5eriod # elements
e&pand "eyond octet #3 electrons$ cannot e&pand "eyond octet
dou"le "onds are preferred dative "onds as last resort
#lone pair from central atom to neigh"our$
Qn 3 Draw the dot'and'cross diagram and 2ewis structure for each substance and
hence eplain the following observations3
(d) C! 0 and 4! have the same number of electron pairs around the central atom,
but show different bond angles.
(d) 'oth have 2 electron pairs directed to the corners of a tetrahedron
CH2
Cx
xx
x
,
,
,
,
C
,
,,
,
Page 6 of 31
http://sg.wrs.yahoo.com/_ylt=A0S0zvjR551J_nQAi1gl4gt.;_ylu=X3oDMTBpdnJhMHUzBHBvcwMxBHNlYwNzcgR2dGlkAw--/SIG=1kumfqjbd/EXP=1235171665/**http%3A/sg.images.search.yahoo.com/images/view%3Fback=http%253A%252F%252Fsg.images.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimage%2526ni%253D18%2526va%253Dbulb%2526fr%253Dyfp-t-web%2526xargs%253D0%2526pstart%253D1%2526b%253D1%26w=253%26h=270%26imgurl=www.istockphoto.com%252Ffile_thumbview_approve%252F184350%252F2%252Fistockphoto_184350_light_bulb.jpg%26rurl=http%253A%252F%252Fwww.eastchester.k12.ny.us%252Fschools%252Fhs%252Fteachers%252Fgorycki%252FBiologySites.htm%26size=9kB%26name=istockphoto_184350_light_bulb.jpg%26p=bulb%26type=JPG%26oid=8d8c8d8c0312810e%26no=1%26tt=1299987%26sigr=12dnc7j6u%26sigi=12ltb8o27%26sigb=13f3ckjbb
8/17/2019 Chemical Bonding Revision (ANSWERS)
7/31
• %here are 2 bond pairs and ' lone pair around C
• C4 is tetrahedral with "ond angle of 1'7+
%H3
x
x
xN ,
,
,
N,
,,
• %here are 3 bond pairs and 1 lone pair around N
• -ince lone pair & bond pair repulsion . bond pair&bond pair repulsion*
• N) is trigonal p,ramidal in shape with bond angle compressed to 1'8 °
Qn 3 Draw the dot'and'cross diagram and 2ewis structure for each substance and
hence eplain the following observations3
(e) "he bond angle in water increases slightly when the ion, ! &%, is formed
(e) H#!
x
x
! ,
,
!
,,
• %here are # bond pairs and # lone pairs around !
• %o minimise repulsion, the 2 electron pairs are directed to corners of a
tetrahedron
•ince lone pair&lone pair repulsion . lone pair&bond pair repulsion .bond pair&bond pair repulsion*
Page 8 of 31
Bond angle decreases with increasing num"er of lone pairs
http://sg.wrs.yahoo.com/_ylt=A0S0zvjR551J_nQAi1gl4gt.;_ylu=X3oDMTBpdnJhMHUzBHBvcwMxBHNlYwNzcgR2dGlkAw--/SIG=1kumfqjbd/EXP=1235171665/**http%3A/sg.images.search.yahoo.com/images/view%3Fback=http%253A%252F%252Fsg.images.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimage%2526ni%253D18%2526va%253Dbulb%2526fr%253Dyfp-t-web%2526xargs%253D0%2526pstart%253D1%2526b%253D1%26w=253%26h=270%26imgurl=www.istockphoto.com%252Ffile_thumbview_approve%252F184350%252F2%252Fistockphoto_184350_light_bulb.jpg%26rurl=http%253A%252F%252Fwww.eastchester.k12.ny.us%252Fschools%252Fhs%252Fteachers%252Fgorycki%252FBiologySites.htm%26size=9kB%26name=istockphoto_184350_light_bulb.jpg%26p=bulb%26type=JPG%26oid=8d8c8d8c0312810e%26no=1%26tt=1299987%26sigr=12dnc7j6u%26sigi=12ltb8o27%26sigb=13f3ckjbb
8/17/2019 Chemical Bonding Revision (ANSWERS)
8/31
• 2! is bent with "ond angle of 1'2+'
H3!9
• ! donates 1 lone pair to H9 with vacant or"ital forming a dative covalent
bond such that there are now 3 bond pairs and 1 lone pair around !
• ince lone pair&bond pair repulsion . bond pair&bond pair
repulsion*• )!
+ is trigonal p,ramidal with "ond angle of 1'8'
Qn 3 Draw the dot'and'cross diagram for each substance and hence eplain the
following observations3
(f)
C C
Cl
,
,
Cl is non'polar, but
Cl
C C
Cl
,, is polar.
(f)
Cl
,Cl
,
,
Cl
,
Cl
C & C C & C
&& &
&&
&&
&&
& &
&&&& &
& &
&&
&
&
'oth isomers have 2 polar CCl "onds with no lone pair around each C
• %he CCl "onds in /st
(trans form) isomer are opposite each other across
Page : of 31
2 structural re5uirements for dative bond:
#a$ lone pair of electrons- #"$ atom with incomplete octet/duplet for H
Bond angle increases "y 2.67
when 1 lone pair is changed to 1 bond pair
x
x
!, ,
,
+
!
, ,,
+
Charge of 91 su"tract / electron from less electronegative H
form a dative bond #lone pair of ! donates to +$
http://sg.wrs.yahoo.com/_ylt=A0S0zvjR551J_nQAi1gl4gt.;_ylu=X3oDMTBpdnJhMHUzBHBvcwMxBHNlYwNzcgR2dGlkAw--/SIG=1kumfqjbd/EXP=1235171665/**http%3A/sg.images.search.yahoo.com/images/view%3Fback=http%253A%252F%252Fsg.images.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimage%2526ni%253D18%2526va%253Dbulb%2526fr%253Dyfp-t-web%2526xargs%253D0%2526pstart%253D1%2526b%253D1%26w=253%26h=270%26imgurl=www.istockphoto.com%252Ffile_thumbview_approve%252F184350%252F2%252Fistockphoto_184350_light_bulb.jpg%26rurl=http%253A%252F%252Fwww.eastchester.k12.ny.us%252Fschools%252Fhs%252Fteachers%252Fgorycki%252FBiologySites.htm%26size=9kB%26name=istockphoto_184350_light_bulb.jpg%26p=bulb%26type=JPG%26oid=8d8c8d8c0312810e%26no=1%26tt=1299987%26sigr=12dnc7j6u%26sigi=12ltb8o27%26sigb=13f3ckjbb
8/17/2019 Chemical Bonding Revision (ANSWERS)
9/31
the C1C "ond such that dipole moments associated with the polar "onds
cancel out exactl,
•
C C
Cl
,
,
Cl is non& polar
• %he CCl "onds in 2nd (cis form) isomer are on the same side of C1C
"ond such that dipole moments associated with the polar "onds do not
cancel out exactl,
•
Cl
C C
Cl
,, is polar
Comparison between the types of structure/bonding
Qn 2 Complete the table below for the following substances in terms of structure
and bonding.
Substance Chemical structure Chemical bond to be overcome during melting / boiling
E.g 5 imple molecular Van der 6aals7 forces of attractionbetween 5 molecules
(a) C! C! $ &! (b) iC (c) Ca&0 (d) Ca
(e) C! C l (f) iC l 0 (g) C! 4! $ (h) 4e
-ubstance Chemical
structure
Chemical bond to be overcome during
melting / boiling
C)C2!
#alcohol$
simple molecular wea8 intermolecular h,drogen bonds
Page 7 of 31
(actors affecting polarity of molecule:
polar bond, ;99;& and lone pair(s)
orientation of polar "ond#s$ in molecule ; idea of
8/17/2019 Chemical Bonding Revision (ANSWERS)
10/31
iC giant molecular strong covalent bonds
"etween i and C atoms
Ca!4 giant ionic lattice strong ionic bonds "etween
oppositely charged ions #ie cations ? anions$Ca giant metallic lattice strong metallic bonds "etween
cations and sea of electrons
C)Cl simple molecular wea8 forces of attraction
due to permanent dipoles #polar molecules$
iCl 4 simple molecular wea8 forces of attraction
due to temporary dipoles #nonpolar
molecules$
C)N2 #amine$
simple molecular wea8 intermolecular h,drogen bonds
Ne
#no"le gas$
simple molecular wea8 forces of attraction
"etween atoms
Qn + n /558, !enri #oissan succeeded in obtaining fluorine by the electrolysis of
molten potassium hydrogen'difluoride, 9!+ $ , which is an ionic compound
containing one cation and one anion.
(i) 6rite the formula of the ions present in 9!+ $ .
Cation: ?9
*nion: @H#@&
(ii) uggest a structure for the anion and state what types of bonding occur
within it.(or (2
:
: / electron #central atom$
/ (: 0 electrons, forms single "ond with #covalent bonding$
/(: 3 electrons, does not form dative "ond with # does not have
empty or"ital to accept$ forms h,drogen bond with
covalent bond
Page 1' of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
11/31
, ((
h,drogen bond
Comparison of the various physical properties
Melting / oiling Point
Qn 6 Eplain the following observations3
(a) Carbon dioide is a gas whereas silicon dioide ( I V) oide is a solid of high
melting point.
• C!2 has a simple molecular structure.
•-maller amount of energy is needed to overcome the weaAer
intermolecular forces of attractions.
• ence, C!2 has a low "oiling point and is a gas.
• i!2 has a giant molecular structure.
• $arger amount of energy is needed to overcome the stronger covalent
bonds "etween i and ! atoms.
Page 11 of 31
o include:
ype of structure
!elative strength of
intermolecular forces of
attraction
Amount of energy
"abel:
# $% on & and $# on ' F
# lone pair of electrons on F
8/17/2019 Chemical Bonding Revision (ANSWERS)
12/31
• ence, i!2 is a solid with high melting point.
(b) "he boiling points of the halogens show a trend.
!lemen
t
boiling point / °C
C l $ ':
*r $ %:1 I $ %/50
• alogens have simple molecular structures
• %o of electrons of halogens increases down the group.
• $arger amount of energy is re5uired to overcome the more extensive
intermolecular forces of attraction down the group
• ence, "oiling point increases down the group.
(c) *utane, C! C! $ C! $ C! , has a higher boiling point than $'methylpropane,
C!(C! ).
• 'oth "utane and 2methylpropane have simple molecular structures
with the same number of electrons
• 'utane is a unbranched (or more elongated) with greater surface area
than 2methylpropane which is branched (or more spherical)
• ore energ, re5uired to overcome the more extensive intermolecular
forces of attraction in "utane.
• ence "utane #C)C2C2C)$ has a higher "oiling point than
2methylpropane #C#C)$)$
Page 1# of 31
or stronger
avoid using stronger> as
same number of electrons
8/17/2019 Chemical Bonding Revision (ANSWERS)
13/31
(d) butane has a lower boiling point than butanol (C! C! $ C! $ C! $ &!)
• 'oth "utane and "utanol have simple molecular structures.
• $ess energ, is re5uired to overcome the weaAer intermolecular forces of attraction in "utane than the stronger
intermolecular h,drogen bonds in "utanol.
•ence "utane has lower "oiling point than "utanol.
Solubility
Qn 8 "he solubilities in water of the three gases are given in the table below3
gas Solubility in
water / mol dm"#
4! /5
!C l $
C&$ ;.;
Each of these gases is soluble in water because it interacts with the solvent.
(i) 6rite e
8/17/2019 Chemical Bonding Revision (ANSWERS)
14/31
• N) can form favourable intermolecular h,drogen bonds with water
molecules
•
Cl dissociates in water to produce ions, hence the ions forms
favourable ion&dipole interaction with water.
ence, "oth ammonia and hydrogen chloride are watersolu"le.
• =eaAer intermolecular forces of attractions in C!2 are
not able to displace the stronger intermolecular h,drogen bonds in
water for hydration.
ence car"on dio&ide is less solu"le in water.
!lectrical Conductivity and others
Qn :(a) =raphite conducts electricity but diamond does not.
•Braphite i s a good conductor of electricity parallel to the layers as non&bonding valence electrons of the car"on atoms are mobile along la,ers to
conduct electricity.
• n diamond, the electrons are localised in the covalent bonds and not
mobile to conduct electricity.
(b) Potassium is good electrical conductor at any states while potassium chloride
conducts in molten state or a
8/17/2019 Chemical Bonding Revision (ANSWERS)
15/31
cations without breaAing the metallic structure as the sea of electrons are
still holding the cations together. ence, copper is ductile.
• n Cu!4, stress applied on the ionic lattice with regular pattern allows causes
sliding of la,ers resulting in ions of similar charges coming together.
%he resultant repulsion shatters the ionic structure. ence, Cu!4 is "rittle.
(d) Ethanoic acid, C $ ! 0&$ in the gas phase >ust above its boiling point has anapparent # r of /$;.
• thanoic acid #C)C!2, r of E7.7$ has an apparent r of /27 which
dou"les the e&pected value.
• ach acid molecule pairs up to form a cyclic #closed ring$ dimer via
intermolecular h,drogen bonds
Combined physical properties
Qn 7
2ead, lead( II ) chloride and lead( I V) chloride have melting points of $? oC, 015 oC
and '/: oC respectively.
(a) Describe the bonding of these three substances and eplain how it accounts
for the above melting points.
• P"Cl 2 has a giant ionic lattice structure with strong electrostatic forces of
attraction between oppositel, charged ions.
$argest amount of energ, is re5uired to overcome the strong ionic bonds ence, P"Cl 2 has the highest melting point.
• P" has a giant metallic lattice structure with strong electrostatic force of
attraction between cations and sea of electrons .
$arge amount of energ, is re5uired to overcome the strong metallic bonds
ence, P" has a high melting point.
Page 1+ of 31
C,) C
!
! ,
C,C
!
!
,δ+δ−
δ+ δ−
δ−
δ−
"abels:
# $% on & and $# on ' * atoms
# lone pair of electrons on *
8/17/2019 Chemical Bonding Revision (ANSWERS)
16/31
• P"Cl 4 has a simple molecular structure with weaA intermolecular forces of attraction.
-mallest amount of energ, is re5uired to overcome the weaAer forces ence, P"Cl 4 has the lowest melting point.
(b) tate and eplain with reasoning the relative solubility of PbC l $ and PbC l 0 in
polar solvents such as water.
•P"Cl 2 can form favourable ion&dipole interactions with water molecules thatresults in the release of energ, to "rea8 the giant ionic lattice structure for
h,dration to occur.
ence, P"Cl 2 is more soluble in water.
• %o favourable interactions "etween P"Cl 4 and water molecules can "e
formed as the weaA intermolecular forces of attraction in
P"Cl 4 are not able to displace the stronger intermolecular h,drogen
bonds of water.
ence, P"Cl 4 is insoluble in water.
(c) tate and eplain the relative electrical conductivity of these chlorides
5bCl # 5bCl 2
Page 16 of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
17/31
• ood conductor in
molten/a0ueous state "ut a non&
conductor in solid state
• %onelectrical
conductor
•n molten>a5ueous state, ions are
mobile to conduct electricity
• n solid state, ions can only
vibrate about fixed positions and
not mobile
•Dlectrons are
localised in covalent
bonds and not mobile to
conduct electricity
$ntegrated %uestion
Qn 1' #odified "@C Prelim $;;5A/A$a,b
(a) ome data on three nitrogen'containing compounds are given in the table
below3Compound
Molecular &ormula
oiling Point / ' C
dinitrogen pentoide 4 $ &: Decomposes
nitric acid !4& 5
nitrosyl chloride 4&Cl '8.0
(i) Draw 2ewis structures to illustrate the shapes of 4 $ &: (a symmetrical
molecule), !4& (with 4 and & as centres) and 4&Cl. ndicate the relevant
bond angles in each case.
N
!
N
!
! !
!
,
!N
!
!
N
Cl!
Page 18 of 31
hemical
onding
8/17/2019 Chemical Bonding Revision (ANSWERS)
18/31
N
!
N
!
! !
!
1#'' 1#'
'1'23+
'
,
!
N
!
!
1'23+'
1#''
N
Cl!
1#''
trigonal planar #a"out each N$ > "ent #a"out central !$ bent (about 4)
(ii)4itrosyl chloride is a yellow gas most commonly encountered as a
decomposition product of a
8/17/2019 Chemical Bonding Revision (ANSWERS)
19/31
#ii$ Get & "e e5uili"rium amount of Cl 2 in mol.
2N!Cl #g$ 2N! #g$ + Cl 2#g$
nitial >mol 7.6 7 7
Change >mol 2& + 2& + &
5uili"rium>mol 7.6 H 2& + 2& + &
%otal e5uili"rium num"er of mol 1 7.6 H 2& + 2& + & 1 7.E700 & 1 7./700
I of N!Cl dissociated 1
20.10!!"
1000.#×
I 1 4)./ I
5art B
@Drilling 5uestions. %hese 5uestions will not "e discussed in class, please chec8 *PF for more information
Qn 1
Describe the structure type of bonding in potassium, calcium oide and hydrogen
iodide. Draw dot'and'cross diagrams to illustrate the arrangement of valence
electrons in calcium oide and hydrogen iodide.
Potassium has a giant metallic lattice structure with strong electrostatic forces
of attraction "etween cations #?9 ) and sea of electrons
Calcium o&ide has a giant ionic lattice structure with strong electrostatic forces
of attraction "etween the oppositel, charged (Ca#9 and !#& ) ions
Page 17 of 31
Chemical
$quilibria
8/17/2019 Chemical Bonding Revision (ANSWERS)
20/31
!xx
x x
xx
2+ 2
Ca xx
l has a simple molecular structure with stronger electrostatic forces of
attraction "etween the nuclei and the shared pair of electron and
weaAer intermolecular van der waals> forces
, xxxxx
xx
Qn #
Complete the table below for the following molecules A ions.
olecule/ion
Eot&and&cross
diagram
$ewis structure -hape/Bond angle
5olarit,(polar/non&
polar)
Central atom
'y Broup No.
Neutral su"stance Cations *nions
(a) Bp II>III 'eCl 2 g! g)N2 '2+ *l Cl 4
(b) Bp I%: C C2E C24 C! C2(+ CN!
(c) Bp %: % N!2 N2!4 N24 N!2+ N!2
(d) Bp % *s'r ) "(6 P!Cl 2+ PCl E
(e) Bp %I: ! !) !'r )!2+ !
(f) Bp %I 2!) 2!4 ($ centres) ()+ !)
2 !42
(g) Bp %II Cl (!2 'r(!) I()! I(4+ Cl (4 Cl !)
Page #' of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
21/31
(h) Bp 7 9e(4 9e!(4 9e!2(2 9e()+
(a) roup II /III
olecule
/ion
Eot&and&cross
diagram
$ewis
structure
-hape / Bond
Fngle
5olarit,
'eCl 2Cl Cl 'e
&&
&&
&&&&
&&
&&
&&
'e Cl Cl Ginear > /377 Nonpolar
g!
g !&&& &
&&
2+ 2 Note: Broup II/III metals form
predominantly ionic bonds with the top
most electronegative atoms: * ! and %g)N2
g
&&&
&&
2+
) 2
)
N
'2+
,& ',
+
,',Ginear > /377 JJ
*l Cl 4
*l
Cl&
&&
&& & &
&& &&
&
&&
&&&
&Cl
&&
& Cl
Cl&&
&&
&&
&
-
&
*l
Cl
ClCl
Cl
- %etrahedral>
/7K.6L
JJ
(b) roup IV: C
olecule
/ion
Eot&and&cross
diagram
$ewis
structure
-hape /
Bond Fngle
5olarit,
C! C !&&&&
&& !C Ginear > /37
7 Polar
C2E
&
&
&&
&
&
&C C
,
,,
,
, ,
C C
,
,,
,
,,
%etrahedral
#a"out each C$ >
/7K.6LNonpolar
C24
&
&&
&&
&C C
,
,,
,C C
, ,
,,
%rigonal planar
#each C$ > /27L Nonpolar
C2(+
&
&
C(
, ,
+
C
(
, ,
+ %rigonal planar>
/277 JJ
CN!
&&&
&N C&&!&&
&&
&&
-C !N
-Ginear > /377
JJ
(c) roup V: N
olecule /ion Eot&and&crossdiagram $ewis structure -hape/Bond angle 5olarit,
Page #1 of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
22/31
N!2
!
N
!&
&
&&
&&
&&
&&
& &
N
!!
lightly "ent >
M/277lightly
polar
N2!4
&&
&&
&&
&&
&&
&
&
&
&
&&
&N N !!
!
!
N N
!
!
!
!
%rigonal planar
#a"out each N$ >
/277
Nonpolar
N24x
x
xx
x
x
x NN,
,,
, N,
,N
,,
%rigonal
pyramidal
#each N$ > /707
Polar
N!2+
x
x
x
xN !!
+N !!
+ Ginear > /377 JJ
N!2
xx
xx
xN !!
N
!
!
'ent > M/277 JJ
(d) roup V
olecule /ion
Eot&and&crossdiagram
$ewis structure -hape/Bond angle
5olarit,
*s'r )
&
&
*s
&
&&
&
& & &&&
&&
&&&
& &
& &&
'r 'r
'r
*s
'r 'r
'r
%rigonal
pyramidal > /707Polar
"(6&
&
&&&
&&
&&
&&
&&
&
&&
&
&&&
&
&&
&
&&&&&
&&&
&&
&
."
((
(
(( ."
(
(
((
(
%rigonal
"ipyramidal >/277 #e5uatorial$
? K77 #a&ial$
Nonpolar
P!Cl 2+
&& &
&
&&
&&
&&
&&&&
&&&&
& &
P !
Cl
Cl
+
P
!
Cl Cl
+%rigonal planar>
/27L
JJ
PCl E
P& &
&&
&
&
ClCl
ClCl
Cl
Cl
-
PCl
Cl
Cl
Cl
Cl
Cl
-
!ctahedral > K77
JJ
(e) roup VI: !
olecule /ion
Eot&and&crossdiagram
$ewis structure -hape/Bond angle
5olarit,
Page ## of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
23/31
!'r 'ent >
M /74.6L
Polar
!)! !
!
& &
&
&&
&&
&&
&&
&
!
!
!
'ent >
M /27L Polar
)!2+ /st !: 'ent>/74.67
2nd !:%rigonal
pyramidal>
/707
JJ
!
! ,&
-! ,
-Ginear > /377
JJ
(f) roup VI:
olecule /ion
Eot&and&crossdiagram
$ewis structure -hape/Bond angle
5olarit,
2!) .
!!
!&
&
&&
&&
&&
&&&
&&
&&
&&
&
,,
.
! !!
, ,
: %rigonal
pyramidal >/707
ach !: "ent >
/74.67
Polar
2!4
.!!
!
&&
&&
&
&
!
&
&
,,
.!
,
! !
!
,
: %etrahedral >
/7K7
ach !: "ent >/74.67
Polar
()+
%rigonal
pyramidal > /707 JJ
!)2
.!
!
2
!&
&&&
&&
&&
&&&&
&&
&&
&&
&&
2
.
! !!
%rigonal
pyramidal > /707 JJ
!42
.!
!
2
!
&&
&&
&&
!
.!
! !
2
!%etrahedral >
/7K.6L
JJ
(g) roup VII
olecule /ion
Eot&and&crossdiagram
$ewis structure -hape/Bond angle
5olarit,
Page #3 of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
24/31
Cl (!2 %rigonal
pyramidal >
/707
Polar
'r(!) %etrahedral >
/7K.6L
Polar
I()!
(I
!
((
ee saw >
M/277 #e5uatorial$
? K77 #a&ial$
Polar
olecule /ion
Eot&and&crossdiagram
$ewis structure -hape/Bond angle
5olarit,
I(4+
(I
((
(ee saw >
M/277
#e5uatorial$
? K77 #a&ial$
JJ
Cl (4
Cl(
(
(
(
&
&&&
&
&&
&&&
&&
&
&&&
&&
&&&
&
&
&& &&
&&
Cl(
(
(
(
5uare planar >
K7o JJ
Cl !)
&&
&&
&&
&&&&
& &
&& & &
&
&&
Cl !
!
!
Cl
!!
!
%rigonal
pyramidal >
/70L
JJ
(h) roup '
olecule
/ion
Eot&and&cross
diagram
$ewis structure -hape/
Bond angle
5olarit,
9e(4
9e&&
& &
(
((
(
&&&&
&&
&&
&&&
&&
&&
&&
&&&&&
&&
9e
( (
((
5uare
planar >
K7o
Non
polar
9e!(4
9e(
(!
(
(
5uare
pyramidal >
K7o
Polar
Page #2 of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
25/31
9e!2(2
9e
(
(
!
!
ee saw >
M/277
#e5uatorial$
? K77 #a&ial$
Polar
9e()+
9e
(
(
(
%shaped >K7o
JJ
Qn 3 N277E>>III>2a
*oron forms simple trihalides of formula * with all the halogens. *+ and *Cl arethe most common. *oth find uses as +riedel'Crafts catalysts since they readily react
with electron pair donors.(i) Describe and eplain the shape of the *+ molecule.
%here are 3 bond pairs and ' lone pairs around B.
%o minimise repulsion, the 3 electron pairs are directed to the corners of an
e0uilateral triangle
ence '() is trigonal planar
(ii) *+ and trimethylamine, (C! )4, react in a /3/ ratio to give a white crystalline solid. Draw a diagram to show the bonding within a molecule of this solid,
eplaining the type of bonding involved. F:G % atom in N#C)$) donates the lone pair of electrons to B with vacant
orbital>incomplete octet forming a co&ordinate (or dative covalent) bond.
Qn 2 Cyanamide, 4! $ C4, is used for organic synthesis in a stable commercial formand it is formed from the acidification of calcium cyanamide, Ca4C4.Cyanamide is also capable of forming an addition product with borontrifluoride, *+ .
(a) 6rite down an e
8/17/2019 Chemical Bonding Revision (ANSWERS)
26/31
(c) tate the li8ely shapes of N2CN and '(), hence draw a diagram toillustrate the li8ely shape of the addition product.
+
N2CN is trigonal p,ramidal, '() is trigonal planar
*ddition product: tetrahedral with respect to each N and ' centre
Qn + 4$;;/A II A$a
- newly discovered source of froHen fuel is Imethane iceJ, also called Kmethane
hydrate7. "his is methane trapped in ice about :;; m to $;;; m below the ocean
surface. Deposits have been detected off 4orway, 4orth Carolina and in the Pacific &cean off @apan, ndonesia and 4ew Lealand.
"he ice in methane hydrate has a more open structure than ordinary ice and
contains spaces large enough to contain methane molecules.
(i) Draw a diagram of a water molecule and eplain why its bond angle is about
/;: o
%here are # bond pairs and # lone pairs around !. %o minimise repulsion,
the 2 electron pairs are directed to the corners of a tetrahedron
ince lone pair&lone pair repulsion . lone pair&bond pair repulsion . bond
pair&bond pair repulsion, "ond angle is compressed to 1'2+' #/76L$
(ii) "he diagram below shows part of the structure of ordinary ice.
Eplain why the bond angles in ice are /;1o.
Page #6 of 31
!
,,
',
(
C
' ( '
(
( '
B&
'C
((
&
&
8/17/2019 Chemical Bonding Revision (ANSWERS)
27/31
n ice, each water molecule forms two h,drogen bonds with its neigh"ouring
water molecules such that each ox,gen atom is surrounded "y four h,drogen
bonded atoms.
%here are a total of 2 bond pairs and ' lone pairs around !,
hence shape is tetrahedral a"out ! and "ond angle is /7KL.
Qn 6 4itrogen and boron combine to form boron nitride, with empirical formula *4,
which has a graphite'lie structure.
(a) *y considering the electron distribution of your above structure, suggest with
reasoning the liely electrical conductivity of boron nitride.
'oron nitride:
• non&conductor of electricity when perpendicular to layers: electrons are
localised in the covalent bonds and not mobile to conduct electricity
• non&conductor of electricity when parallel to layers. $one pairs of
electrons on % atoms are held closel, to the highl, electronegative %
atom and are not mobile to conduct electricity.
(b) uggest one probable industrial application of boron nitride.
• t could "e used as a machiner, lubricant
Qn 8 4a4 hydrolyses slowly in water to form hydraHoic acid, !4 .
(a) Draw the dot and cross diagram for ionic compound, 4a4 .
'
(b) Eplain why 4a4 has low solubility in heane, an organic solvent in
terms of chemical structure and bonding.
• NaN) has a giant ionic lattice structure with strong ionic "onds.
Page #8 of 31
Na NN N
8/17/2019 Chemical Bonding Revision (ANSWERS)
28/31
• e&ane has a simple molecular structure with weaA intermolecular
forces of attraction.
• ence, no favourable ion&dipole interactions "etween ions and non
polar he&ane molecules can "e formed to breaA down the giant ioniclattice structure.
Qn : - student is given oides of elements , , *+ , and their properties are givenbelow3
ormula
of oxide
elting point / oC Fppearance at
rtp
Conductivit,
=!2 /077 Ohite solid None
2! 7 Colourless li5uid Poor
G! 2367 Ohite solid Bood in molten state
!2 0) Colourless gas None
he was told that the four samples could be water, silicon dioide, carbon dioide or magnesium oide.(a) dentify the four oides.
ormula of oxide Identit,
=!2 ilicon dio&ide
2! Oater
G! agnesium o&ide
!2 Car"on dio&ide
(b) Eplain your reasoning for the identification of $ &, based on the physical properties given (i.e. its melting point and conductivity in molten state).
2! -imple molecular structure
• -maller amount of energ, is needed to "rea8 the relativel, weaAer
intermolecular h,drogen bonds, hence low melting point.
• Poor electrical conductor "ecause electrons are localised in the
covalent bonds and not mobile to conduct electricity
(c) Eplain why the melting point of * & is higher than , &$ .
G! iant ionic lattice structure
$arger amount of energ, is needed to "rea8 the stronger ionic
bonds
!2 -imple molecular structure
-mall amount of energ, is needed to "rea8 the weaAer
intermolecular forces of attraction
(d) Eplain why * & can conduct electricity in molten state but not &$.
G! Bood electrical conductor in molten state: ions are mobile to conductelectricity
Page #: of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
29/31
=!2 Non electrical conductor: electrons are localised in the covalent
bonds in the giant molecular structure,
hence, not mobile to conduct electricity
5art C
%hese 5uestions are for su"mission and answer will "e posted on *PF. Eeadline
for submission4 JJJJJJJJ
Qn 1 Kotal 1' marAs (-tandard F level)
Ethene, C $ ! 0, and hydraHine, 4 $ ! 0, are hydrides of elements which are ad>acent inthe Periodic "able. Data about ethene and hydraHine are given in the table below.
C24 N24
melting point>oC /EK +2
"oiling point>oC /74 +//4
solu"ility in water nsolu"le high
solu"ility in ethanol high high
(a) Ethene and hydraHine have a similar arrangement of atoms but differently shaped molecules.
(i) 6hat is the !'C'! bond angle in etheneM 'ond angle: 1#'' L1@
(ii) Draw a Kdot'and'cross7 diagram for hydraHine.
x
x
xx
x
x
x NN,
,,
,
L1@
(iii) 6hat is the !'4'! bond angle in hydraHineM 'ond angle: 1'8 ' L1@
(iv) tate and eplain whether hydraHine is polar or non'polar.L+@
N "ond is polar and there is 1 lone pair around each N
N24 is trigonal p,ramidal about each % such that the dipole momentsassociated with the polar "onds and lone pair do not cancel out e&actly. L1@
N24 is polar L1@
(b) "he melting and boiling points of hydraHine are much higher than those of ethene. uggest reasons for these differences in terms of the intermolecular forces each compound possesses.L#@
'oth have simple molecular structures.
Page #7 of 31
8/17/2019 Chemical Bonding Revision (ANSWERS)
30/31
ore energy is re5uired to overcome the stronger intermolecular h,drogenbonding in h,draMine than the weaAer intermolecular forcesof attraction in ethene. ence higher melting ? "oiling of hydraine than ethene.
(c) Eplain, with the aid of a diagram showing lone pairs of electrons and dipoles,
why hydraHine is very soluble in ethanol.L3@
Qn # Kotal 1' marAs (ore Challenging)
(a) Cyanogen, a highly toic gas can be represented by the formula, (C4)$ . 6hen
sub>ected to etremely high pressure, a non'conducting solid is formed.
Nesearch done suggested that the electrical conductivity of the solid could beincreased by inserting certain atoms into its structure for eample, caesium.
(i) Draw the dot and cross diagram of a cyanogen molecule.
L1@
L1 or '@
(ii) Determine with reasoning the shape of the cyanogen molecule.
L#@
%here are # bond pairs and ' lone pairs around C .
%o minimise repulsion, the # electron pairs are directed to opposite
sides of each other L1@
Cyanogen is linear L1@
(iii) Eplain how the introduction of caesium enhances the electrical
conductivity of cyanogen.
L1@
Caesium has a giant metallic lattice structure with mobile electrons
to enhance the electrical conductivity of cyanogen. L1@
(b) Cyanide poisoning occurs when a living organism is eposed to cyanide ions.
Common life threatening chemicals include cyanide salts such as potassium
cyanide.(i) Draw the dot and cross diagram for cyanide ion. =iven that cyanide ion
has a linear shape, predict its 2ewis structure. L#@
Page 3' of 31
C% C %
%C %C
δ−
δ+
δ+C2,6 ,
!
hydrogen"onds
δ−
δ+
C2,6
N
,,
,
!
N
,,
δ−1m show>state hydrogen "ond1m draw N24 and C26!1m show lone pairs and partial charges
8/17/2019 Chemical Bonding Revision (ANSWERS)
31/31
L1 or '@ L1 ecf@
(ii) Predict and eplain how you would epect the boiling point of
potassium cyanide to compare with hydrogen fluoride.
L2@
Potassium cyanide has a giant ionic lattice structure while
ydrogen fluoride has a simple molecular structure. L1@
$arger amount of energ, is re5uired to overcome the stronger ionic
bonds L1@ in QCN than the weaAer intermolecular h,drogen bonds
in CN L1@.
Potassium cyanide will have a higher L1@ "oiling point compared to
hydrogen fluoride.
Recommended