FORMAL CHARGEFORMAL CHARGE

Formal ChargeFormal Charge

N:. .. ..

N:.. ..H

H

NH2-

BondedUnbonded

Number of All One half of = valence electrons unshared + all shared in the neutral electrons electrons atom

( Formal Charge = 5 - 4 - 2 = -1 )

5e- 6e-

LEWIS DIAGRAMS SHOW IT ALL !LEWIS DIAGRAMS SHOW IT ALL !- all atoms including hydrogens - all bonds (lines not dots )- all unshared pairs ( dots )- all formal charges - all atoms with octets ( except H )- the correct number of electrons ( count! )

When drawing a Lewis Diagram remember these rules.

Rumus KimiaRumus Kimia

Rumus empirikRumus MolekulRumus struktur

Rumus struktur lengkapRumus struktur panjang (expanded)Rumus struktur termampatkan (condensed)

Rumus Struktur pada Rumus Struktur pada senyawa siklis – sikloheksanasenyawa siklis – sikloheksana

Expanded formula

C

CC

C

CC

H HH

H

HHH

H

H HH

H

C6H12

Rumus Struktur pada Rumus Struktur pada senyawa siklis – sikloheksanasenyawa siklis – sikloheksana

Polygon formula(condensed formula)

C6H12

Rumus Struktur pada senyawa Rumus Struktur pada senyawa siklis – sikloheksanasiklis – sikloheksana

Condensed formula

C6H12

CH2

CH2CH2

CH2

CH2

CH2

Contoh Molekul siklisContoh Molekul siklis

C C

C

CH2 CH2

CH2

H H

H

HH

H

C

C C

C CH2

CH2 CH2

CH2

H

H

H

H

H H

HH

C C

CC

C

CH2 CH2

CH2

CH2CH2

H H

H

H

H

H

H HHH

Cyclopropane C3H6

Cyclobutane C4H8

Cyclopentane C5H10

Beberapa cara penulisan strukturBeberapa cara penulisan struktur

H

O

citronellal(CH3)2C=CHCH2CH2CH(CH3)CH2CHO

C CHH3C

H3CCH2 CH2 C

CH3

H

CH2 CH

Oor

CC C

H

HH

H

HH

CC H

H

CH

H CH

C

CH H

H

C

HH

O

H

expanded

condensed

line

line structures are most compactand easy to read

Molekul polar dan Nonpolar

• To determine if a molecule is polar, we need to determine – if the molecule has polar bonds– the arrangement of these bonds in space

• Molecular dipole moment (Molecular dipole moment ():): the vector sum of the individual bond dipole moments in a molecule– reported in debyes (D)

Bond Dipole Moments

• are due to differences in electronegativity.• depend on the amount of charge and

distance of separation.• In debyes, x (electron charge) x d(angstroms)

Molecular Dipole Moments• Depend on bond polarity and bond angles. • Vector sum of the bond dipole moments.• Lone pairs of electrons contribute to the

dipole moment.

Polar and Nonpolar Molecules

• these molecules have polar bonds, but each has a zero dipole moment

O C O

Carbon dioxide = 0 D

BF

FF

Boron trifluoride = 0 D

C

Cl

ClClClCarbon tetrachloride

= 0 D

Polar and Nonpolar Molecules• these molecules have polar bonds and

are polar moleculesN

HH

HO

H H

Water = 1.85D

Ammonia = 1.47D

directionof dipolemoment

directionof dipolemoment

Polar and Nonpolar Molecules

– formaldehyde has polar bonds and is a polar molecule

Formaldehyde = 2.33 D

directionof dipolemoment H HC

O

Intermolecular Forces

• Strength of attractions between molecules influence m.p., b.p., and solubility; esp. for solids and liquids.

• Classification depends on structure.– Dipole-dipole interactions– London dispersions– Hydrogen bonding

Dipole-Dipole

=>

Dipole-Dipole Forces

• Between polar molecules• Positive end of one molecule aligns with

negative end of another molecule.• Lower energy than repulsions, so net force

is attractive.• Larger dipoles cause higher boiling points

and higher heats of vaporization.

London Dispersions

• Between nonpolar molecules• Temporary dipole-dipole interactions• Larger atoms are more polarizable.• Branching lowers b.p. because of

decreased surface contact between molecules.

=>

CH3 CH2 CH2 CH2 CH3

n-pentane, b.p. = 36°CCH3 CH

CH3

CH2 CH3

isopentane, b.p. = 28°C

C

CH3

CH3

CH3

H3C

neopentane, b.p. = 10°C

Dispersions

=>

Hydrogen Bonding

• Strong dipole-dipole attraction• Organic molecule must have N-H or O-H.• The hydrogen from one molecule is

strongly attracted to a lone pair of electrons on the other molecule.

• O-H more polar than N-H, so stronger hydrogen bonding

H Bonds

Boiling Points and Intermolecular Forces

CH3 CH2 OHethanol, b.p. = 78°C

CH3 O CH3

dimethyl ether, b.p. = -25°C

trimethylamine, b.p. 3.5°C

N CH3H3C

CH3

propylamine, b.p. 49°C

CH3CH2CH2 N

H

H

ethylmethylamine, b.p. 37°C

N CH3CH3CH2

H

CH3 CH2 OHethanol, b.p. = 78°C ethyl amine, b.p. 17°C

CH3 CH2 NH2

ASAM DAN BASA

Brønsted-Lowry Theory of Acids and Bases

• Acid:Proton Donor• Base: Proton Acceptor

Conjugate Acid: Base + Proton

Conjugate Base: Acid - Proton

Strong Acids and Bases

• Strong acid - completely ionized in aqueous solution. Examples are:– HCl, HBr, HI, HNO3, HClO4, and H2SO4

• Strong base - completely ionized in aqueous solution. Examples are:– LiOH, NaOH, KOH, Ca(OH)2, and Ba(OH)2

Weak Acids and Bases• Acetic acid is a weak acid

– it is incompletely ionized in aqueous solution

Base(weaker base)

Acid(weaker acid)

Conjugate baseof CH3CO2H

(stronger base)

Conjugate acidof H2O

(stronger acid)

CH3COH + H2 O

+ H3 O+CH3CO-

O

O

Lewis Theory of Acids and Bases

• Acid: Electron-Pair Acceptor– Electrophile

• Base: Electron-Pair Donor– Nucleophile

Weak Acids and Bases

• The equation for the ionization of a weak acid, HA, in water and the acid ionization constant, Ka, for this equilibrium are

=

HA H3O++A-

[H3O+][A -][HA]

Ka

+ H2O

= Keq[H2O]

pKa = - log Ka

Weak Acids and Bases

Acid Formula pKaConjugate Base

ethanolwaterbicarbonate ionammonium ioncarbonic acidacetic acidsulfuric acidhydrogen chloride

10.3315.715.9

4.766.369.24

-5.2-7

CH3CH2OH CH3CH2O-

H2O HO-

HCO3- CO3

2-

NH4+ NH3

H2CO3 HCO3-

CH3CO2H CH3CO2-

H2SO4 HSO4-

HCl Cl -

Acidity Constant (Ka)

HA + H2OK

A- + H3O+

K =[A-] [H3O+]

[H2O][HA]

Ka = [A-] [H3O+]

[HA]K [H2O] =

pKa = - log Ka

pKa

pKa = - log Kaa

Strong acid = large Ka = small pKaa

Weak acid = Weak acid = small Ka = large pKaa

Relative Acid Strength

HClO4 ClO4_stronger

weaker

ACIDSTRENGTH

weaker

stronger

BASESTRENGTH

ACID CONJ. BASE Ka pKa

10 -1010

1.8 x 10 4.8-5

1.0 x 10 10-10

10 50-50

OH O

CH3 C OH

O

CH3 C O

O

CH3 CH3 CH3 CH2

_

Acid Strength

• Strong Acid– Conjugate base is weak– pKa is small

• Weak Acid– Conjugate base is strong– pKa is large

Base Strength

• Strong Base– Conjugate acid is weak– pKa is large

• Weak Base– Conjugate acid is strong– pKa is small

Position of equilibrium

• Favors reaction of the stronger acid and stronger base to give the weaker acid and weaker base

++Stronger acid

Stronger base

Weaker base

Weaker acid

HA B- A- HB

(weaker acid)(stronger acid)pKa 9.24pKa 4.76

+ + Acetic acid Ammonium ionCH3CO2H NH3 CH3CO2

- NH4+

Position of equilibrium

• Stronger acid and stronger base react to give weaker acid and weaker base

Carbonic acidpKa 6.36

PhenolpKa 9.95

++C6 H5OH HCO3- C6 H5O- H2 CO3

Bicarbonateion

Phenoxideion

+ +Acetic acidBicarbonate

ionAcetate

ionCarbonic acid

pKa 4.76 pKa 6.36

CH3 CO2H HCO3- CH3 CO2

- H2 CO3