updated jawapan chapter 3 chemical bonding

8/16/2019 Updated Jawapan Chapter 3 Chemical Bonding

1/23

CHAPTER 3: CHEMICAL BONDING

SUBJECTIVE QUESTIONS3.1 Lewis Str!tre

Q1

A

Valence electrons are electrons in the outermost shell of an atom.

Q"

A

A Lewis symbol is the symbol of an element with one or more dots around it. These dots

represent the number of valence electrons in an atom of the element.

Q3

A

P

Q#

A

The tendency of an atom to achieve a configuration where its valence shell contains eight

electrons.

Q$

A

30Zn!" # s s p$ 3 s 3 p$ 3d #0 %pseudonoble gas configuration&

3'(r ) " # s s p$ 3 s 3 p$ 3d #0 * s * p$ %noble gas configuration&

'+n!" # s s p$ 3 s 3 p$ 3d ' %half,filled orbitals&

1

---

--


2/23

Q%

A

The transfer of electrons from an atom to an electronegative atom forms cations and anions.

The electrostatic force of attraction between these oppositely charged ions produces an ionic bond.

Q&

A

The electronic configurations of sodium and fluorine are"

a" # s

s

p

$

3 s

#

/" # s s p'

The transfer of an electron from a atom to / atom produces a! and / ) ions.

Therefore the formula of the compound is a/.

Q'

A

Lithium atom Li has one valence electron. 1ach Li atom loses one electron to produce Li !

ion.

itrogen atom has five valence electrons. atom should receive three electrons to achieve

the noble gas configuration. Thus one atom must react with three Li atoms to form one 3)

ion and three Li! ions.

2


3/23

Q(

A

The electronic configuration of magnesium is # s s p$ 3 s. +g has two valence electrons

hence it tends to lose these electrons to achieve a noble gas configuration. Therefore thestable ion formed is +g! with the electronic configuration of # s s p$. The electronic

configuration of chlorine is # s s p 3 s 3 p'. Thus 2l needs to gain one electron to achieve

the noble gas configuration. ence the stable ion formed is 2l ) %# s s p$ 3 s 3 p$&.

To form a neutral compound out of +g! and 2l ) ions we need two 2l ) ions per +g! ion. 4o

the formula is +g2l.

+g! ion is very unstable because it does not have the noble gas configuration. Therefore

+g2# does not e5ist as a stable compound.

Q1)

A

A covalent bond is the bond formed when two atoms share one or more pairs of electrons. 6t

is usually formed between the non,metal elements. 15ample" 2l %chlorine gas&

Therefore the covalent bonding in 2# is due to the sharing of a pair of electrons by two 2l

atoms.

An ionic bond is the electrostatic attraction between two oppositely charged ions.

15ample" a2l

7ne electron from a sodium atom is transferred to a chlorine atom forming ions. The

electrostatic attraction between a! and 2l ) ions forms the ionic bond.

3


4/23

Q11

A

Q1"

A

Q13

A

Q1#

A

Q1$

A

A covalent bond formed when a pair of electrons is contributed by only one of the bonded

atoms.

4


5/23

Q1%

A

1. The donor atom must have a lone pair of electrons.

". The acceptor atom must have an empty orbital to accommodate the pair of electrons.

Q1&

A

Al3! has empty orbitals.

Al3!"

3 s 3 p 3d

1ach of the / ) ions uses one lone pair of electrons to form coordinate covalent bonds with si5

empty orbitals of the Al3! ion.

Q1'

A

/ormal charges on"

ydrogen 8 # ) # 8 0

4ingly bonded carbon 8 * ) * 8 0

2arbon 8 * ) * 8 0

itrogen 8 ' ) ' 8 0

5


6/23

Q1(

A

(a) /ormal charges"

ydrogen 8 # ) # 8 0

75ygen %bonded to & 8 $ ) $ 8 0

itrogen 8 ' ) * 8 !#

75ygen 8 $ ) $ 8 0

%double bonded&

75ygen 8 $ ) 9 8 )#

%singly bonded&

The formal charges of o5ygen and nitrogen are )# and !# respectively while formal charges

of other atoms are :ero. Therefore the sum of formal charges is :ero. Thus this is a neutral

molecule.

(b) /ormal charges"

ydrogen 8 # ) # 8 0

2arbon 8 * ) * 8 0

75ygen 8 $ ) $ 8 0

%doubly bonded&

75ygen 8 $ ) 9 8 )#

%singly bonded&

4ince the formal charge of singly bonded o5ygen is )# therefore this formula represents anion %formate ion 277 ) &.

6


7/23

Q")

A

/ormal charges" /ormal charges"

4ulphur 8 $ ) $ 8 0 4ulphur 8 $ ) 9 8 )#

2arbon 8 * ) * 8 0 %singly bonded&

4ulphur 8 $ ) ' 8 !#

%triply bonded&

2arbon 8 * ) * 8 0

The structure 48284 is preferred because each atom has a formal charge of :ero.

The structure 4)2;4 is not preferred because a positive charge is placed on a very

electronegative atom 4.

Q"1

A

Q""

A

Lewis structures having the same arrangement of atoms but differ from one another in the

position of their electrons.

Q"3

A

A single structure which represents the actual contribution of resonance structures.

7


8/23

Q"#

A

Q"$

A

3." M*+e!+,r S-,e ,/0 P*+,rit

Q"%

A

The electron,pairs around the central atom are orientated as far apart as possible to minimisethe repulsion among them.

Q"&

A

A lone pair of electrons is the electron,pair that is part of an atom


9/23

Q"'

A

Q"(

A

Q3)

A

Trigonal planar bent

The central atoms of both molecules are surrounded by three electron,pairs. (2l 3 has three

bonding pairs around the central atom ( and these electrons repel each other e=ually.Therefore the molecular shape of (2l3 is trigonal planar with #0> bond angles.

4n2l has two bonding pairs and one lone pair. The stronger repulsion between the lone pair

and the bonding pairs tends to compress the bonding pairs in 4n2l closer. Thus the bond

angle in 4n2l is ?'> which is less than the e5pected trigonal planar angle of #0>.

9


10/23

Q31

A

Q3"

A

75ygen in 7 is surrounded by four electron,pairs %two bonding pairs and two lone pairs&.

The bond angles in 37! becomes larger because one lone pair from the o5ygen atom of the

water molecule bonds covalently to ! to form a 37! ion. Thus o5ygen in 37

! is

surrounded by three bonding pairs and one lone pair.

Therefore the bond angle is larger in 37!

as there is only one lone pair compared with twolone pairs in 7.

Q33

A

A polar bond is covalent bond formed between two bonded atoms of different

electronegativity in which the electrons are not e=ually shared. Thus one atom has a partial

positive charge and the other atom has a partial negative charge.

15ample"

2hlorine is more electronegative than hydrogen. Therefore chlorine attracts the bonding

electrons more strongly and closer to it giving the partial negative chargeδ ) on 2l atom

and partial positive chargeδ

! on atom. Thus the bond in ))2l is polar.

10


11/23

Q3#

A

1. 4hape of molecule.". The difference in electronegativities between atoms in a bond.

Q3$

A

1lectron affinity is the heat change when an electron is added to a gaseous atom or ion to

form a gaseous ion.

1lectronegativity is a measure of the ability of an atom in a molecule to attract electrons to

itself.

Q3%

A

2/* has the same tetrahedral shape as 22l3/. 1ach 2))/ bond in 2/* is polar because

fluorine is more electronegative than carbon. owever dipole moment of the bonds cancel

each other so 2/* is a non,polar molecule.

6n 22l3/ fluorine is more electronegative than chlorine. Thus the dipole moment of the

bonds cannot cancel each other. As a result the net dipole moment is pointing towards

fluorine. 4o 22l3/ is a polar molecule.

11


12/23

Q3&

A

/luorine is more electronegative than iodine. 4o the bond dipoles point toward fluorine. The

e=uatorial bond dipoles cancel each other because they point in opposite directions. 4ince

there is one lone pair at the central atom the a5ial dipole is not cancelled. Thus 6/ ' is a polar

molecule.

Q3'

A

The molecular shape of (/3 is trigonal planar which is symmetrical. Although each bond is

polar the bond dipole moments cancel each other. Therefore (/3 is a non,polar molecule.

The molecular shape of P/3 is trigonal pyramidal which is not symmetrical. The bond dipole

moments do not cancel each other and P/3 is a polar molecule.

Q3(

A

(3 @ 3 @ /3

6ncreasing dipole moment

Q#)

A

4ince 27 has no dipole moment the two 287 bond moments must e5actly cancel each

other. This can occur only if the two bonds are in a straight line. Therefore the shape of 27

is linear.

12


13/23

3.3 Or2it,+ Oer+, ,/0 H2ri0is,ti*/

Q#1

A

The mi5ing of different types of atomic orbitals to produce a set of e=uivalent hybrid orbitals.

Q#"

A

P/$ ) " sp3d 62l*

!" sp3d

Q#3

A

Q##

A

Pi,bond %& is formed by sideways overlapping of p atomic orbitals.

4igma,bond % σ

& is formed by the head,on overlapping of atomic orbitals.

15ample" 7verlapping of s and p orbitals.

13


14/23

Q#$

A

" /"

# s s p

The # s orbital of hydrogen atom overlaps with an unpaired electron in the p orbital of

fluorine to produce a σ ,bond in /.

/"

s p

1ach / atom uses its unpaired electron in the p orbital to produce a σ ,bond in /.

Q#%

A

The orbital diagram for valence electrons in nitrogen" "

s p

The nitrogen atom has three unpaired electrons. The electron will not be promoted from s

orbital to p orbital. owever s and p orbitals hybridised to form sp3 orbitals.

sp3 hybrid orbitals

sp3

orbitals of nitrogen overlap with s orbital of hydrogen atom.

14

↿↿↿↿↿

↿↿↿↿

↿↿

↿


15/23

Q#&

A

P %ground state&"

3 s 3 p 3d

7ne of the 3 s electrons can be promoted into an empty 3d orbital.

P %e5cited state&"

3 s 3 p 3d

/ive single electrons to form five covalent bonds in P26'

The 3 s 3 p and 3d orbitals are hybridised to form five sp3d hybrid orbitals.

sp3d hybrid orbitals

1ach sp3d orbital of nitrogen overlaps with a p orbital of chlorine atom. The shape of this

molecule is trigonal bipyramidal.

15

↿↿↿↿

↿↿↿↿

↿↿↿


16/23

Q#'

A

Q#(

A

2 %ground state&"

s p

2 %e5cited state&"

s p

A carbon atom is bonded to two other atoms. Therefore a carbon atom will form two sp

hybrid orbitals.

2"

hybridised sp orbitals unhybridised p orbitals

3.# I/ter4*+e!+,r 5*r!es

Q$)

A

Propane" London forces

16

↿↿↿

↿↿↿↿

↿↿↿↿


17/23

Propanol" ydrogen bonds

Propanone" Bipole,dipole attraction

Q$1

A

1 +olecular si:e

2 +olecular shape

3 Polarity of molecules

Q$"

A

The boiling point of a substance is influenced by the strength of the intermolecular forces and

not by the strength of the covalent bonds within the molecules because vaporising of a li=uid

involves separating the molecules from one another and it does not involve the breaCing of

covalent bonds within the molecules. Thus its vapour contains e5actly the same molecules as

in the li=uid.

Q$3

A

@ e @ 2* @ De

Q$#

A

(oth molecules are non,polar molecules but 2(r * has a higher molecular weight compared to

22l*.

Therefore the van der Eaals forces between 2(r * molecules are higher. As a result 2(r * has

a higher boiling point.

17


18/23

Q$$

A

The hydrogen bonding results from the intermolecular attraction between the hydrogen atom

in a polar bond %particularly )/ )7 or )& and a lone pair of electrons on a highly

electronegative atom of / 7 or on another molecule.

The hydrogen bond e5ists between a hydrogen atom in an 3 molecule and the nitrogen

atom of an adFacent 3 molecule.

Q$%

A

/ has the lowest boiling point because / is a non,polar molecule and thus have London

dispersion forces. 2l is a polar molecule and thus dipole,dipole forces occur betweenmolecules which is stronger than London dispersion forces.

237 is also a polar molecule and it has hydrogen bonding between its molecules.

ydrogen bonds are stronger intermolecular forces than dipole,dipole forces. ence 237

has the highest boiling point.

Q$&

A

1thanol is more soluble in water than chloroethane because ethanol is polar and has an 7)

group that can form hydrogen bonds with water molecules whereas chloroethane cannot

form hydrogen bonds with water molecules even though it is a polar molecule.

18


19/23

Q$'

A

(oth compounds have hydrogen bonds between their molecules. Eater molecules can form

twice as many hydrogen bonds as /. The total strength of four hydrogen bonds of water

molecules e5ceed the total strength of two hydrogen bonds of / molecules. ence water

has a higher boiling point than /.

Q$(

A

(oth molecules form hydrogen bonds intermolecularly but water has stronger hydrogen

bonds than ammonia as the o5ygen atom is more electronegative than the nitrogen atom.

Thus water has a higher boiling point.

Q%)

A

(a2l is an ionic compound. The molecules are held strongly by the electrostatic force.

ence (a2l has a higher boiling point. 2* is a simple covalent compound and has weaC

van der Eaals forces acting between molecules. 2* has a lower boiling point.

19


20/23

3.$ Met,++i! B*/0

Q%1

A

A metallic bond is the electrostatic attraction between the positively charged metal and the

sea of delocalised electrons.

Q%"

A

+agnesium conducts electricity due to the delocalised electrons which can move freely

throughout the metal and carry an electric current.

4ulphur has a molecular structure and its electrons are in fi5ed positions in the atom and

cannot move throughout the solid. Thus sulphur does not conduct electricity.

Q%3

A

Aluminium is metallic. +etallic bonds are stronger thus the melting point of aluminium is

much higher. Aluminium chloride has a lower melting point due to the weaC van der Eaals

forces that e5ist between the Al2l3 molecules.

Q%#

A

(oth aluminium and sodium are metallic. The strength of a metallic bond depends on the

number of valence electrons. 4ince aluminium has three valence electrons and sodium has

one valence electron the metallic bonds in aluminium are stronger than sodium. Therefore

aluminium has a higher melting point than that of sodium.

20


21/23

CHALLENGE QUESTIONS

Str!tre0 Qesti*/s

1.a& i&

ii& T,shaped

iii& sp3d

b& i&

ii& * bonding pairs and lone pairs. 6odine is in Period ' of the Periodic Table. 6t has

empty 'd orbitals so it can e5pand its octet.

".a& 0Y " # s

s p$ 3 s 3 p$ * s

? Z " # s s p'

b& YZ c& Z %covalent bond&

Ess, Qesti*/s

1.a& 4pecies B.

a2l is an ionic compound. The molecules are held strongly by the strong

electrostatic forces. ence it has higher boiling and melting points. 4olid a2l does

not conduct electricity because the ions are fi5ed in a lattice but it can conduct

electricity in a=ueous solution and in the molten state because the ions are able to

move freely.

b& 4pecies D.

21


22/23

A covalent molecule has relatively low melting and boiling points because the

molecules are held by weaC van der Eaals forces. 6t also does not conduct electricity

when in solid or molten states as there are no delocalised electrons.

c& 2opper is metallic. +etallic bonds are stronger thus the melting point and boiling

point of copper should be higher. 2opper conducts electricity in both solid and molten

states.

d& 7n melting the particles remain close together and they are Fust loosened from

their lattice position.

7n vaporising the molecules of a li=uid must overcome their intermolecular forces in

order to separate and form vapour. The greater the intermolecular forces the greater

the energy re=uired to pull the molecules away from each other thus the boiling point

is higher.

".a& 2ovalent bonds.

b& Van der Eaals forces.

c& (oth 2)2l and 2)/ bonds are polar bonds since 2l and / arem ore electronegative

than 2 atom.

2/2l3 is a polar molecule because the dipole moment of the bonds cannot cancel each

other. 2/2l3 has a tetrahedral shape.

d& (oth are polar molecules.

2/2l has a lower boiling point because it has a lower molecular mass than that of

2/2l3. The smaller the molecular mass the weaCer the van der Eaals forces and the

lower the boiling point.

3.a& $2 " # s

s p

b& )2;2)

ethynei& 2%ground state&"

22

↿↿↿


23/23

s p

2%e5cited state&"

s p

7ne electron from s orbital is promoted to p orbital.

ii& sp

iii&

23

↿↿↿↿

updated jawapan chapter 3 chemical bonding

Documents