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 H

H

H

H

HH

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

C

C

C

CH2 CH2

CH2

CH2

CH2

H H

H

H

H

H

HH

HH

Cyclopropane C3H6

Cyclobutane C4H8

Cyclopentane C5H10

Beberapa cara penulisan strukturBeberapa cara penulisan struktur

H

O

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

C CH

H3C

H3C

CH2 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

B

F

F

F

Boron trifluoride = 0 D

C

Cl

ClClCl

Carbon tetrachloride = 0 D

Polar and Nonpolar Molecules• these molecules have polar bonds and

are polar moleculesN

HH

H

O

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 H

C

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°C

CH3 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 OH

ethanol, 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 OH

ethanol, 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

ethanol

water

bicarbonate ion

ammonium ion

carbonic acid

acetic acid

sulfuric acidhydrogen chloride

10.33

15.7

15.9

4.76

6.36

9.24

-5.2

-7

CH3CH2OH CH3CH2O-

H2O HO-

HCO3-

CO32-

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 CH3CH3 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 ion

CH3CO2H 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 acidBicarbonateion

Acetateion

Carbonic acidpKa 4.76 pKa 6.36

CH3 CO2H HCO3-

CH3 CO2-

H2 CO3