Chemical Bonding Revision (ANSWERS)

8/17/2019 Chemical Bonding Revision (ANSWERS)

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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


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


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


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.

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-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



(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



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$



(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



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 °



(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



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 +$



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


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


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


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


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


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


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 *


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


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


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


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


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


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


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


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



5olarit,

Page ## of 31


23/31

!'r 'ent >

M /74.6L

Polar

!)! !

!

& &

&

&&

&&

&&

&&

&

!

!

!

'ent >

M /27L Polar

)!2+ /st !: 'ent>/74.67

2nd !:%rigonal

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olecule /ion



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5olarit,

Page #3 of 31


24/31

Cl (!2 %rigonal

pyramidal >

/707

Polar

'r(!) %etrahedral >

/7K.6L

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M/277 #e5uatorial$

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Page #2 of 31


25/31

9e!2(2

9e

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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


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

((

&

&


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


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


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


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


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.

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Chemical Bonding Revision (ANSWERS)