intramolecular forces and intermolecular forces

7/25/2019 Intramolecular Forces and Intermolecular Forces

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INTRAMOLECULAR FORCES AND INTERMOLECULAR

FORCES

*Review

Name Formula Electron dot diagram

Water H2O

Carbon dioxide CO2

Carbon monoxide CO

Ammonia NH3

Sulfur dioxide SO2

*Dierence !etween intramolecular orce" and intermolecular orce"

Intra = within Inter = between

Intramolecular orce" #covalent !ond$ Intermolecular orce"

1. Strong

2. Within molecules

3. Determine chemical roerties !reaction"

Wea#

$et%een molecules

Determine h&sical roerties. eg. melting and

boiling oints.

INTRAMOLECULAR FORCES

%& S'A(ES OF MOLECULES

'he shae of molecules are determined based on the (alence Shell )lectron *air +eulsion

'heor& !(S)*+"

,t has 2 main rinciles

1. )lectron airs around the central atom in a molecule reel one another as far as aart as

ossible.

2. -one air lone air reulsion / lone air bonding air reulsion

'his means the shae of a molecule is determined b& the number of bonding airs and lone airs

around the central atom.


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hae

Difference of

atoms in the

molecule

Difference of

atoms around

central atom

Difference of

lone e around

central atom

Difference of

bonding around

central atom

Name of shae )xamle of mo

0

02 -inear H2 CO

0 3 2 4 5 or 6 or 7 -inear CO2 !

0

3 2 2 or 5 5 or 6 $ent or ( shaed H2O !

0

5 3 4 6 or 7

'rigonal lanar

or triangular

lanar

$83!

0

5 3 2 6

*&ramidal or

trigonal

&ramidal

NH3! N

H H H

0

9 5 4 7 'etrahedral

CH5!

)& ONDIN+ (OLARIT,

onding

1. Co:alent bonding in:ol:es sharingof electrons.

2. 'he atoms in co:alent bonds are nonmetal and semimetalatoms.

3. 'he atoms ma& be of different or samet&es.

5. 'he abilit& of an atom to attract electrons to itself in a chemical bond is called

electronegativityt&es.

9. 'he abilit& to attract electrons in a chemical bond increases going across a eriod and

decreasesgoing do%n a grou.


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6. 8or co:alent molecules of an element. )g. O2 Cl2 etc. the difference in electronegati:it&

bet%een the 2 atoms in the molecule iszero.

* $ond olarit& describes ho% e;uall& bonding electrons are shared bet%een a air of atoms in a

co:alent bond.

< ,f the electrons are"-ared e.uall/0 the bond is anon1olar covalent !ond&

< ,f the electrons are"-ared une.uall/ !one atom has greater attraction" then the bond is a1olar

covalent !ond&

We can use electronegati:it& difference !)N" to determine %hether a bond is olar or non olar.

EN rage ond 1olarit/

4 4.5 Non olar bond

4.9 1.6 *olar co:alent bond

1.= 1.> *olar co:alent if no metal is in:ol:ed but ionic if there is a metal? 2.4 ,onic

Note@ ,f a bond olar then the more electronegati:e atom becomes artiall& negati:e ! " and the

less electronegati:e atom becomes artiall& ositi:e !B"

2& MOLECULAR (OLARIT,

When a co:alent bond is olar the atoms in:ol:ed %ill ha:e a diole artial ositi:e and artial

negati:e charge"

A molecule is olar if it has

1. *olar co:alent bonds and

2. ns&mmetrical or non s&mmetrical distribution of charge.

A molecule is s&mmetrical if it has an e:en distribution of charge.

'he charge includes the t&e of atom and gi:e of electrons in:ol:ed.

)g.

is s&mmetrical because the Cl atoms are e:enl& distributed around the

$ atom and there are no lone air electrons.


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H is uns&mmetrical because the t&es of atoms around the $ atom are

$ different.

Cl Cl

Note@ S&mmetrical@ no lone air electron surround central atom and the same atoms surround

central atom.

Symmetrical - non olar Unsymmetrical -olar

):en distribution means the charges are at e;ual angles and of the same t&e.

,f a molecule has olar co:alent bonds and is uns&mmetrical then it %ill ha:e a net diole

!similar to a net force" in one direction.

,f a molecule has olar bonds but is s&mmetrical then its diole %ill cancel out and the net diole

%ill be ero. So the molecule %ill be non olar.

< Some molecules are slightl& olar if the& ha:e nonolar co:alent bonds but are uns&mmetrical.

3& E4ERCISES

Determine t-e "-a1e" o t-e ollowing molecule" and t-e 1olarit/ o t-e !ond" !etween

t-eir atom"&

Formula Name o t-e "-a1e (olarit/1. NCl3 pyramidal Non polar bond

2. *H33. $Cl3 !$ Eust need 6 electrons"

5. CH3Cl

9. SO26. N2O

Com1lete t-e ollowing ta!le

Formula Lewi" "tructure Molecular "-a1e Name o "-a1e (olarit/

82 N F N -inear Non olar

H2O

HCl

CH5NH3


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C$r5CS2SO2H2CO

H2Se

INTERMOLECULAR FORCES

%& T,(E OF INTERMOLECULAR FORCES

1e o orce(olarit/ o

molecule"E5am1le o "u!"tance Origin o t-e orce

Factor t-at determin

"trengt-

Di"1er"ion

ce

Gain force

bet%een non olar

molecules but also

found bet%eenolar molecules

'emorar& une:en

distribution of electron

cloud around a molecule

resulting in temorar&dioles in neighbouring

molecules. 'his results in

a temorar& attraction.

1. Ho% closel& the mol

are ac#ed !the closer

stronger the force"

2. 'he sies of the elecclouds !count the total

difference of electrons

molecules".

Di1ole6

ole orce

8ound bet%een

olar molecules

onl&

*ermanent attraction

bet%een artial ositi:e

and artial negati:e ends

of neighbouring olar

molecules.

'he net diole of the

molecules also determ

b& ho% olar the bonds

'/drogen

nd

8ound bet%een

olar molecules

%ith HN H8 or

HO bonds !olar"

Attraction bet%een highl&

artial ositi:e H atoms

and lone electrons on a

highl& electronegati:e

%ith a olar molecule.

'he number of H atom

lone electrons combina

a:ailable to form h&dro

bonds.

on6di1ole

ce

8ound bet%een

ositi:e or

negati:e ion andolar molecule

Attraction bet%een

oosite charges !artial

ositi:e atom andnegati:e ion or artial

negati:e and ositi:e ion".

1. 'he charge of the ion

in:ol:ed !the greater th

charge the stronger theattraction IF ionic sie

e;ual".

2. 'he olarit& of the

molecules in:ol:ed !th

more olar the stronge

attraction".


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Ion 7 di1ole orce 8 -/drogen !onding 8 di1ole 7 di1ole orce 8 di"1er"ion orce

*Review

T/1e o intermolecular orce E5am1le o "u!"tance wit- t-i" orce

1. Disersion force CO22. Diole diole force H2S

3. H&drogen bonding H8

5. ,on diole force Cl !a;"

)& (',SICAL (RO(ERTIES

Melting and !oiling 1oint"

'he melting oint of H2O is 4oC and its boiling oint is 144 oC.

'he strength of intermolecular forces in co:alent molecular substances

determine ho% high their melting and boiling oints are.

When comaring their melting oints and boiling oints %e must consider@

1. 'he olarit& of the substances.

2. 'he t&e of intermolecular forces resent.3. 'he strengths of the forces and amount of energ& needed to brea# them.

E5am1le&

%& E51lain w-/ CO -a" a -ig-er !oiling 1oint t-an CO )&

CO is a olar co:alent substance %ith diole diole and disersion forces bet%een its

molecules.

CO2is a non olar substance %ith disersion forces bet%een its molecules.

'he combination of diole diole and disersion forces in CO is stronger and need more heat

energ& to be bro#en than the disersion forces in CO2.

)& E51lain w-/ Cl)-a" a -ig-er !oiling 1oint t-an O)&

$oth Cl2and O2are non olar co:alent substances %ith disersion force bet%een their molecules.

Ho%e:er Cl2has more electrons bet%een its molecules and roduces stronger disersion forces

than in O2so disersion forces in Cl2need more heat energ& to be bro#en.

2& E51lain w-/ C%9'))-a" -ig-er !oiling 1oint t-an 'F&


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C14H22 is a non olar substance %ith disersion forces bet%een its molecules.

H8 is a olar co:alent substance %ith disersion forces diole diole forces and h&drogen

bond bet%een its molecules.

'he combination of disersion forces diole diole forces and h&drogen bond in H8 is strongerbut C14H22has much more electrons bet%een its molecules so it %ill roduces much more

stronger disersion forces so C14H22 need more heat energ& to be bro#en.

* Possible comparisions between melting and boiling points of substances

Su!"tance A*olar molecule

%ith small sie

Non olar molecule

%ith small sie

*olar molecule %ith H

bonding

Su!"tance Non olarmolecule %ith

small sie

Non olar molecule

%ith bigger sie

Non olar moleculemuch bigger ! about 7

14 times"

Su!"tance wit- -ig-er

!oiling 1oint and melting

1oint

Substance A Substance B Substance B

* Other difference that may affect melting and boiling points

1. Golecules %ith the same molecular formula but difference structural formula due to resence

of branches. 'he less branched has higher boiling oint

Eg&$utane and meth&l roane

2. '%o olar substances %ith h&drogen bonding and %ith similar molecular sies but difference

ossibilities to form h&drogen bonds.

< 'he substance %ith more h&drogen bonds has higher melting and boiling oints.

Eg. H2O has higher melting and boiling oints than NH3and H8.

Solu!ilit/

Solubilit& is the maximum amount of a substance !called a solute" that can dissol:e in a fixed

amount of another substance !called the sol:ent".


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'he "olute is the substance in a smaller amount and the "olvent is the substance in larger

amount.

Eg&in a salt %ater the solute is salt and the sol:ent is %ater.

'he temerature at %hich solubilit& is measured must be stated since solubilit& changes astemerature increase or decreases.

8or substance to dissol:e in another the follo%ing rocesses must occur.

1. 'he solute solute bond brea#.2. the sol:ent sol:ent bonds brea#

3. Ne% solute sol:ent bonds are e;ual.

,f solute sol:ent bonds are stronger than or similar to the solute solute and sol:ent sol:ent

bonds then the solute can dissol:e.

,f not then the solute cannot dissol:e.

'he bonds resonsible for solubilit& co:alent substances are intermolecular forces.

'o redict if a solute is soluble in another substance %e need to@

1. Determine the olarit& of the t%o substances.

2. Determine the solute solute and sol:ent sol:ent intermolecular forces.

3. Determine the ossible solute sol:ent intermolecular forces.

5. Comare the strength of the solute sol:ent intermolecular force to the solute solute and

sol:ent sol:ent intermolecular force.

'he general rule for solubilit& is that Ili#e dissol:e li#eI. 'his means olar solutes dissol:e in

olar sol:ents and non olar solutes dissol:e in non olar sol:ent.

Ho%e:er ionic solutes also dissol:e in olar sol:ents. Some substances are artl& olar and

artl& non olar sol:ents 'he& cannot as sol:ents for olar and non olar solutes.

* Summary of solubility outcomes between ionic polar covalent and non polar covalent

substances

Solute Solvent Solu!ilit/

1. olar substance *olar substance Soluble2. ionic substance *olar substance Soluble deend on solubilit&

rules for ionic substances

3. ionic substance Non olar substance ,nsoluble

5. olar substance Non olar substance ,nsoluble

9. non olar substance Non olar substance Soluble

6. artl& olar and artl& non *olar substance Soluble but solubilit& decrease as


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olar substance the non olar art gets bigger

=. artl& olar and artl& non

olar substance

Non olar substance Soluble but solubilit& decrease as

the non olar art gets smaller

* !"ample of polar covalent non polar covalent and ionic substances

T/1e o "u!"tance E5am1le"

1. *olar co:alent sol:ent Water !H2O"

)thanol !CH3CH2OH"

Carbox&lic acids !CnH2nB1COOH"

2. Non olar co:alent sol:ents erosene

*etrol Oils

Geth&lbenene

3. *artl& olar and artl& non olar sol:ents )thanol !CH3CH2OH"

Alcohol !CnH2nB1OH"

5. ,onic solutes NaCl Cl Gg$r 2 CuSO5

* !"planation chec#list

1. Which is the more suitable sol:entJ

2. What is the olarit& of each substanceJ

3. What t&e of intermolecular forces are found in each substanceJ

5. What forces are formed %hen the substances are mixedJ

9. Ho% strong are the ne% forces formed comared to forces in each substance.

:a1our 1re""ure

(aour is the gaseous state of a substance that is normall& li;uid at room temerature.

*ressure is the force of collision bet%een articles and the %alls of their container.

(aour ressure or e;uilibrium :aour ressure is a measure of the tendenc& or abilit& of

substance to e:aorate !change from li.uidto ga"".


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%& ;-at need" to -a11en or a "u!"tance to eva1orate

intramolecular forces and intermolecular forces

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