Exam 3 Wednesday 3 December See Mini-quizzes 24-34 + octet rule structures + formal charge.
FORMAL CHARGE
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Transcript of FORMAL CHARGE
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