Bab 6-Ik Kimia-printable (1)

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Ikatan Kimia

• Konsep dalam Ikatan Kimia

• Simbol Lewis

•Ikatan ionik dan Struktur Lewis

•Ikatan kovalen dan struktur Lewis

•Jenis-jenis ikatan kovalen : tulen,

datif dan berkutub



Konsep asas dalam ikatan kimia

Sebatianionikdankovalenadalahduasebatianyangumumdengansifatfizikyangberbezayangberasaskankepadapembentukanikatanmasing2.

Kata kunci

• Sebatian Ionikterbentukdaripadainteraksikuat(dayaelektrostatik)

antaraion-ion.Ion-ionwujudhasilpendermaandanpenerimaanelektron

atom-atom.Dayaelektrostatikantaraionyangwujudmenghasilkan

perbezaansifatfizikmisalnyatakatleburataukekonduksianelektrik.

• Sebatian kovalenmelibatkanperkongsianelektronantaraatom-atom.

Akibatperkongsianelektron,sifatfizikyangterhasilialahtakatlebur

yangrendahdankekonduksianelektrikyangrendah.

*Selainikionik&kovalen,terdapatbanyaklagidayayangmenghasilkan

ikatanantaraatom-atom.



SIMBOL TITIK LEWIS

• Apabila suatu atom berinteraksi bagi membentuk ikatan kimia,hanya elektron valens sahaja yg berhubung.

• Ahli kimia menggunakan sistem titik untuk menunjukkan yang jumlah elektron bagi atom tidak berubah. 1 titik untuk 1elektron valens.



Elektron Valens adalah elektron terluar (elektron di petala

terluar) suatu atom. Hanya e valens yg terlibat dalam

pembentukan ikatan.

1A 1Cth: 2.1

2A 2Cth: 2.8.23A 3Cth: 2.8.3

4A 4Cth: 2.4

5A 5Cth: 2.5

6A 6Cth: 2.8.6

7A 7Cth: 2.7

Kumpulan # e valensKonfigurasi e





Contoh:

Tulis simbol Lewis bagi atom natrium dan ion natrium.

Jwpn: atom Na, Z = 11

konfigurasi e : 2.8.1

elektron valens : 1

atom natrium : Na •

ion natrium : [ Na ]+



Contoh

Tulis simbol Lewis bagi atom oksigen dan ion oksida.

Jwpn : atom oksigen O, Z = 8

konfigurasi e : 2.6

elektron valens : 6

Atom oksigen :

ion oksida : [ ]2-



Ik. Ionik

Suatu sebatian ionik terbentuk drpd gabungan ion positif dan negatif.Ion-ion dalam sebatian ionik dipegang oleh daya elektrostatik

Pembentukan kation

Atom logam, M menyingkir elektron bagi membentuk ion positif (kation)

M M+ + e

Pembentukan anion Atom bukan logam, X menerima e valens bagi membentuk ion negatif

(anion)

X + e X-



Pembentukan sebatian ionik

Kation M+ dan anion X- bergabung dengan ikatan ionik bgmembentuk sebatian ionik .

M+ + X- MX

Ikatan kimia dalam MX adalah tarikan antara cas positif ion M

dengan cas negatif ion X. Sebatian MX secara elektriknyaneutral.



Li + F Li+ F -

2.1 2.72 2.8

[He] [Ne]

Li Li+ + e-

e- + F F -

F -Li+ + Li+ F -

contoh Tbls antara litium dan florin bagi membentuk

litium florida.

( kation )

( Anion )



2Ca( p) + O2(g ) 2CaO( p)

contoh kalsium terbakar dalam oksigen dan

membentuk kalsium oksida.

2.8.8.2 2.6 [Ar] [Ne]

Latihan

Gunakan simbol titik Lewis utk menunjukkan pembentukan :

(i) Magnesium nitrida, Mg3N2(ii) Aluminium oksida, Al2O3



Ik kovalen ialah ik kimia di mana 2 atau lebih elektron

dikongsikan.

Mengapa atom-atom berkongsi elektron?

FF+

7e- 7e-

F F

8e- 8e-

F F

F F

Struktur Lewis F2

Psgn e sendiri

Ik. Kovalen tunggal

Ikatan kovalen

Psgn e sendiri

Psgn e sendiri Psgn esendiri

Ik. Kovalen tunggal



8e-

H HO+ + OH H O HHor

2e- 2e-

Str Lewis air

Ik. berganda – 2 atom berkongsi 2 pasang e

Ik kov tunggal

O C O atau O C O

8e- 8e- 8e- Ik dubel

Ik ganda 3 – 2 atom berkongsi 3 pasang e

N N

8e- 8e-

N N

Ik tripel

atau



1. Lukis str kerangka sebatian dengan atom jum

minimum (atau paling elektropositif) di tengah(atom pusat). Letak atom2 lain di keliling atompusat (atom hujung).

2. Hitung jum e valens. Tambah 1 pd setiap 1 casnegatif dan tolak 1 bagi setiap cas positif.

3. Lengkapkan oktet semua atom hujung terlebihdahulu, Oktet bg H ialah 2!

4. Jika struktur mengandungi lebihan e, bentukkanik dubel atau tripel dgn atom pusat sebgmnperlu.

Melukis str Lewis sebat kovalen



Penulisan struktur Lewis bagi nitrogen triflorida (NF3).

Lgkh 1 – N kurang elektronegatif dari F, letak N di tengah

F N F

F

Lgkh 2 – Kira e valens bagi N - 5 (2s22p3) dan F - 7 (2s22p5)

5 + (3 × 7) = 26 e valens

Lgkh 3 – Lukis ik tunggal antara atom N dan F dan lengkapkan

oktet bagi atom N dan F.

Lgkh 4 - Semak, adakah e dalam struktur = bil e valens ?

3 ik. tunggal (3×2) + 10 e sendiri (10×2) = 26 e valens



16

Write the Lewis structure of the carbonate ion (CO32-).

Step 1 – C is less electronegative than O, put C in center

O C O

O

Step 2 –

Count valence electrons C - 4 (2s2

2p2

) and O - 6 (2s2

2p4

)-2 charge – 2e-

4 + (3 x 6) + 2 = 24 valence electrons

Step 3 – Draw single bonds between C and O atoms and complete

octet on C and O atoms.Step 4 - Check, are # of e- in structure equal to number of valence e- ?

3 single bonds (3x2) + 10 lone pairs (10x2) = 26 valence electrons

Step 5 - Too many electrons, form double bond and re-check # of e-

2 single bonds (2x2) = 4

1 double bond = 4

8 lone pairs (8x2) = 16

Total = 24



17

Struktur Lewis dan Cas Formal

1. Bagi molekul neutral, struktur Lewis dengan cas formal

sifar adalah yang terbaik/paling stabil berbanding struktur

dengan nilai cas formal.

2. Struktur Lewis dengan nilai cas formal yang besar

adalah kurang stabil berbanding struktur dengan nilai cas

yg kurang.

3. Jika terdapat lebih dari 1 struktur, yang lebih stabil ialah

agihan cas (-) yang diletakkan pada atom elektronegatif.

Struktur mana yang lebih mungkin untuk CH2O?

H C O H

-1 +1 HC O

H

0 0



2 struktur kerangka bagi formaldehid (CH2O)

H C O HH

C OH

Cas formal suatu atom ialah perbezaan antara e valens bagi

atom asal dengan bil e yang ditetapkan dalam struktur Lewis.

Cas formal

satu atom dlm

struktur Lewis=

1

2

Jum e ikatan

( )

Jum e valens

dalam atom

bebas -Jum e bukan

ikatan -

Jum cas formal bagi semua atom dalam molekul atau ion =

cas bersih molekul / ion.



H C O H

C – 4 e-

O – 6 e-

2H – 2×1 e-

12 e-

2 ik tunggal (2×2) = 4

1 ik dubel = 4

2 psg e sendiri (2×2) = 4

Total = 12

Cas formal C = 4 - 2 - ½ × 6 = -1

= 6 - 2 - ½ × 6 = +1

Cas formal

suatu atom

dalam struktur

Lewis

=1

2

Jum e ikatan

( )

Jum e valens

dalam atom

bebas -Jum e bukan

ikatan -

-1 +1

Cas formal O



2 0

C – 4 e-

O – 6 e-

2H – 2x1 e-

12 e-


1 double bond = 4


Total = 12

HC O

H

formal charge

on C= 4 - 0 - ½ x 8 = 0

formal charge

on O= 6 - 4 - ½ x 4 = 0

formal charge

on an atom in

a Lewis

structure

=1

2

total number

of bonding

electrons

( )

total number

of valence

electrons in

the free atom

-total number

of nonbonding

electrons

-

0 0

9.7



Struktur resonans ialah satu atau lebih struktur yang boleh

mewakili dengan tepat sesuatu struktur Lewis molekul.

O O O+ -

OOO+-

O C O

O

- -O C O

O

-

-

OCO

O

-

-

Apakah struktur resonans bagi ion

karbonat (CO32-)?



H F FH

Ik kovalen berkutub adalah ik kovalen denganketumpatan elektron yang tidak sekata antara 2 atom.

Kaw kaya

elektron

Kaw kurang

elektron e- riche- poor

d+ d-



Ke-elektronegatifan ialah kebolehan suatu atom untuk menarik

elektron kepadanya dalam suatu ikatan kimia.

Afiniti Elektron – boleh diukur, Cl tertinggi

Ke-Elektronegatifan - relatif , F tertinggi

X (g) + e- X-(g)





25



26



kovalen

kongsi e-

Kovalen berkutubpartial transfer of e-

Ionik

pemindahan e-

Perbezaan keelektronegatifan meningkat

Klasifikasi ikatan yang bergantung kpd perbezaan keelektronegatifan

perbezaan Jenis ikatan

0 kovalen 2 Ionik

0 < dan <2 Kovalen berkutub



28

Kelaskan yang berikut sebagai ionik, kov berkutub,atau kovalen: ik dlm CsCl; dalam H2S danthe NN bond in H2NNH2.

Cs – 0.7 Cl – 3.0 3.0 – 0.7 = 2.3 Ionik

H – 2.1 S – 2.5 2.5 – 2.1 = 0.4 Kovalen berkutub

N – 3.0 N – 3.0 3.0 – 3.0 = 0 Kovalen

f C



29

Bond

Type

Bond

Length

(pm)

C-C 154

C C 133

C C 120

C-N 143

C

N 138C N 116

Lengths of Covalent Bonds

Bond Lengths

Triple bond < Double Bond < Single Bond 9.4



3 0

DativeCovalentBondorCoordinateCovalentBond

Covalentbondformsbetweentwoatomsthatdonateanelectroneach.

However,itispossibleforbothelectronstocomefromthesame

atom.Thisisknownasadativecovalentbond oracoordinate

covalentbond.

Theatomthatdonatetheelectronsisknownasthedonor andit

musthaveatleastonelonepairofelectrons.

Theotheratomthatsharestheelectronsisknownastheacceptor

anditmusthaveanincompleteoctet .



31

Example1

Example2



3 2

Exceptions to the Octet Rule

The Incomplete Octet

H HBeBe – 2e-

2H – 2x1e-

4e-

BeH2

BF3

B – 3e-

3F – 3x7e- 24e-

F B F

F


9 lone pairs (9x2) = 18Total = 24

9.9



3 3

Exceptions to the Octet Rule

Odd-Electron Molecules

N – 5e- O – 6e-

11e-

NO N O

The Expanded Octet (central atom with principal quantum number n > 2)

SF6 S – 6e-

6F – 42e-

48e- S

F

F

F

F

F

F



Total = 48

9.9



3 4

Hydrogen Bonding

A hydrogen atom in a polar bond (e.g. H-F, H-O or H-N) canexperience an attractive force with a neighboring electronegativemolecule or ion which has an unshared pair of electrons (usually anF, O or N atom on another molecule)

Hydrogen bonds are considered to be dipole-dipole type interactions

A bond between hydrogen and an electronegative atom such as F, Oor N is quite polar:



35

• The hydrogen atom has no inner core of electrons, so the side of theatom facing away from the bond represents a virtually naked nucleus

• This positive charge is attracted to the negative charge of anelectronegative atom in a nearby molecule

• Because the hydrogen atom in a polar bond is electron-deficient onone side (i.e. the side opposite from the covalent polar bond) this sideof the hydrogen atom can get quite close to a neighboringelectronegative atom (with a partial negative charge) and interactstrongly with it (remember, the closer it can get, the stronger the

electrostatic attraction)

Hydrogen bonds vary from about 4 kJ/mol to 25 kJ/mol sothey are still weaker than typical covalent bonds.

But they are stronger than dipole-dipole and or dispersion

forces. They are very important in the organization of biological

molecules, especially in influencing the structure ofproteins

W t i l i it bilit t f t i h d b di



3 6

Water is unusual in its ability to form an extensive hydrogen bondingnetwork

• As a liquid the kinetic energy of the molecules preventsan extensive ordered network of hydrogen bonds

• When cooled to a solid the water molecules organizeinto an arrangement which maximizes the attractiveinteractions of the hydrogen bonds

• This arrangement of molecules has greater volume(is less dense) than liquid water, thus water expandswhen frozen• The arrangement has a hexagonal geometry

(involving six molecules in a ring structure) which isthe structural basis of the six-sidedness seen in snowflakes

• Each water molecule can participate in fourhydrogen bonds

- One with each non-bonding pair of electrons- One with each H atom



3 7

Metallic Bond

Assume that a metallic lattice is composed of closely packed positiveions surrounded by an electron cloud. This happen when metal atoms

lose their valence electrons, forming metal cations, and the valenceelectrons then make up the electron cloud. The attractive force betweenthe electron cloud and the positive ions called the metallic bond.

The strength of the metallic bond is inversely proportional to the size

of the ion and directly proportional to the number of valenceelectrons on the metal atom. The smaller the size of the cation and/orthe more electrons supplied by the atoms to electron cloud, thestronger is the attractive force between the positively charged ionand the electron cloud. Hence, the stronger is the metallic bond

formed.



3 8

Intermolecular Forces

Intermolecularforcesaregenerallymuch weakerthancovalent

bonds.Only16kJ/molofenergyisrequiredtoovercomethe

intermolecularattractionbetweenHClmoleculesintheliquidstate

(i.e.theenergyrequiredtovaporizethesample)

However,431kJ/molofenergyisrequiredtobreakthecovalent

bondbetweentheHandClatomsintheHClmolecule

Thus, when a molecular substance changes states the atoms within

the molecule are unchanged

Thetemperatureatwhichaliquidboilsreflectsthekineticenergy

neededtoovercometheattractiveintermolecularforces(likewise,

thetemperatureatwhichasolidmelts).

Thus, the strength of the intermolecular forces determines the

physical properties of the substance



3 9

Attractiveforcesbetweenneutral molecules

Attractiveforcesbetweenneutralandcharged ionic) molecules

ion - dipoleforces

Note that all of these forces will be electrostatic in nature

Typically,dipole-dipoleanddispersionforcesaregrouped

togetherandtermedvan der W aals forces (sometimesthe

hydrogenbondingforcesarealsoincludedwiththisgroup)

Dipole - dipoleforces

London dispersionforces

Hydrogen bondingforces



4 0

Ion-dipole

Involvesaninteractionbetweenacharged ionandapolar

molecule (i.e.amoleculewithadipole)•Cations areattractedtothenegativeendofadipole

• Anions areattractedtothepositiveendofadipole

Ion-dipoleforcesareimportantinsolutionsofionicsubstances

inpolarsolvents(e.g.asaltinaqueoussolvent)



4 1

Dipole-Dipole Forces

Adipole-dipoleforceexistsbetweenneutralpolarmolecules

Polarmoleculesattractoneanotherwhenthepartialpositive charge ononemoleculeisnearthepartialnegativecharge onthe

othermolecule.

Thepolarmoleculesmustbeincloseproximityforthedipole-dipole

forcestobesignificant.

Dipole-dipole forcesarecharacteristicallyweakerthanion-dipoleforces.

Dipole-dipoleforcesincreasewithanincreaseinthepolarityofthe

molecule.



4 2

Nonpolar moleculeswouldnotseemtohaveanybasisforattractive

interactions.However,gasesofnonpolarmolecules canbeliquefiedindicatingthatifthekineticenergyisreduced,sometypeofattractive

forcecanpredominate.

FritzLondon(1930)suggestedthatthemotionofelectronswithinan

atomornon-polarmoleculecanresultinatransientdipolemoment.

London Dispersion Forces

A Model To Explain London Dispersion Forces: Helium atoms 2e)

Considertheparticlenatureofelectrons.

Theaveragedistributionofelectronsaroundeachnucleusis

sphericallysymmetrical.

Theatomsarenon-polarandpossesnodipolemoment.Thedistributionofelectronsaroundanindividualatom, at a given

instant in time,maynotbeperfectlysymmetrical.



43

•Bothelectronsmaybeononesideofthenucleus

•Theatomwouldhaveanapparentdipolemomentatthatinstantin

time(i.e.atransientdipole)

•Acloseneighboringatomwouldbeinfluencedbythisapparent

dipole-theelectronsoftheneighboringatomwouldmoveawayfromthenegativeregionofthedipole

Due to electron repulsion, a temporary dipole on one atom can

induce a similar dipole on a neighboring atom

•Thiswillcausetheneighboringatomstobeattracted to one another•ThisiscalledtheLondondispersionforce(orjustdispersionforce)

•Itissignificantonlywhentheatomsareclose together



4 4

Theeasewithwhichanexternalelectricfieldcaninduceadipole

(altertheelectrondistribution)withamoleculeisreferredtoasthe

"polarizability"ofthatmolecule.

Thegreaterthepolarizabilityofamoleculetheeasieritistoinducea

momentarydipoleandthestrongerthedispersionforces

Largermoleculestendtohavegreaterpolarizability

Theirelectronsarefurtherawayfromthenucleus(any

asymmetricdistributionproducesalargerdipoleduetolarger

chargeseparation)

Thenumberofelectronsisgreater(higherprobabilityof

asymmetricdistribution)

thus, dispersion forces tend to increase w ith increasing molecular mass

Dispersionforcesarealsopresentbetweenpolar/non-polarand

polar/polarmolecules(i.e.betweenallmolecules)



Exercise

2. Use the octet rule and draw the Lewis structure of each ofthe following substances or ions, keeping in mind that oneH atom in a compound cannot be bonded to another H

atom.

(a) OH

-

(b) H3O+

(c) NH4

+

(d) NH2

- (e) SH - (f) H3S+

4 5

1. Write Lewis symbols for the following:

(a) P (b) Te (c) Br (d) B

(e) Mn2+ (f) Mn3+ (g) Pb2+ (h) Pb4+



4 6

4. Determine the formal charges for the following

compounds, considering all possible Lewis structuresif there are more than one.

(a) SO2 (b) NH3 (c) H2SO4

3.WriteLewisstructuresforthefollowingcovalent

molecules:

(a)HNNN(hydrazoicacid)

(b)H2NCN(cyanamide)

(c)CH3NH2(methylamine)

5. Draw the possible structures of HNO2 and use formalcharge to pick the most likely. The order of atoms is

HONO.



4 7

7. What happens to the valence shells of Rb and Cl whenthese elements react to form an ionic compound. What

is the formula of this compound?.

6. Write the Lewis structure for acetate ion ( CH3COO- ),

including resonance structures if appropriate.

8. Give the empirical formulas and names of thecompounds formed from the following pairs of ions:

(a) Rb+ and I- (b) Cs+ and SO42-

(c) Sr 2+ and N3- (d) Al3+ and S2-

9. Write the Lewis dot symbols of the reactants andproducts in the following reactions. ( First balance the

equations.)

(a) Sr + Se SrSe (b) Li + N2 Li3N



4 8

10. The atom of element A has a nuclear charge of +11.

Atom B requires two electrons to achieve an octet

( A and B are not the actual symbols of the elements).

(a) By using Lewis structures, show the formation of the

compound formed when element A combine

with element B.

(b) Can the solid compound formed conduct electricity?.

Explain briefly.

11. Phosphonium ion, PH4+ is formed when phosphene,

PH3 combine with H+ ion via a type of bond. By using

the Lewis structure show the formation of the PH4+ ion

and label this new bond.



12. Using Lewis structures, show the formation of a dative

covalent bond between

(i) NH3 molecule and H+ ion

(ii) phosphorus chloride, PCl3 and oxygen, O.

13. With the aid of a suitable diagram, describe a metallic

bond according to the electron cloud model.

14. Arrange the following substances, NaF, HF, F2 and

CF4 in order of increasing boiling points. Explain briefly

your answer.

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Bab 6-Ik Kimia-printable (1)