molecular geometries and bonding theorie

Molecular Geometries
and Bonding Theories
Molecular
Geometries
and Bonding

Molecular Shapes
• we’ve learned to draw Lewis structures and
account for all the valence electrons in a
molecule.
• But: Lewis structures are two dimensional and
molecules are 3 dimensional objects.
Struktur Lewis  2D
molekul  3D
• The 3D structure is absolutely critical for
understanding molecules.
Molecular
Geometries
and Bonding

Molecular Shapes

Bentuk Molekul
• geometry & shape of
molecule critical
• we can easily predict
the 3D structure of a
molecule just by
adding up:
• bound atoms +
lone pairs
Molecular
Geometries
and Bonding

What Determines the
Shape of a Molecule?

• atoms and lone pairs take
up space and prefer to be
as far from each other as
possible

lone pair

atom dan pasangan elektron bebas
(PEB) menempati ruang dan
cenderung berada dlm posisi sejauh
mungkin dgn yg lain

• shape can be predicted
from simple geometry

bonds

bentuk dpt diprediksi
menggunakan geometri
sederhana
Molecular
Geometries
and Bonding

“Things”
“sesuatu”
• The central atom has four
“things” around it. A “thing” is
an atom or a lone pair of
electrons.
Atom “pusat” punya 4 “sesuatu”.
“Sesuatu” bisa berupa atom atau
PEB

• # things = atoms plus lone
pairs
•

#sesuatu = atom + PEB
Molecular
Geometries
and Bonding

Valence Shell Electron

Pair Repulsion Theory
(VSEPR)

“The best
arrangement of a
given number of
things is the one
that minimizes the
repulsions among
them.”

Susunan terbaik 
yang meminimalkan
interaksi tolakmenolak

Molecular
Geometries
and Bonding

number of

things arrangement geometry

bond angles

Geometries
These are the
geometries for two
through six things
around a central atom.
 Geometri utk 2-6
“sesuatu” di sekeliling
atom “pusat”

You must learn these!
Molecular
Geometries
and Bonding

Geometries

• All one must do is count the number of “things” in the
Lewis structure.
Hitung jumlah “sesuatu” dalam struktur Lewis

• The geometry will be that which corresponds to that
number of “things.”
Geometrinya akan bersesuaian dgn jumlah “sesuatu”

Molecular
Geometries
and Bonding

Molecular Geometries

• The geometry is often not the shape of the molecule,
however.
Geometri seringkali bukan “bentuk” dari molekul

• The “shape” is defined by the positions of only the
atoms in the molecules, not the lone pairs.

“Bentuk” ditentukan HANYA oleh posisi atom dlm molekul,
bukan PEB.
Molecular
Geometries
and Bonding

Geometries vs. shape
Within each
geometry, there
might be more than
one shape.
Untuk tiap geometri 
ada lebih dari satu
bentuk yg mungkin
Molecular
Geometries
and Bonding

Linear geometry

two things
things geometry atoms lone pairs

shape

example

• In this geometry, there is only one molecular geometry:
linear.
Geometri linier  bentuk linier

• NOTE: If there are only two atoms in the molecule, the
molecule will be linear no matter what the geometry is.
Dua atom  LINIER

Molecular
Geometries
and Bonding

Trigonal Planar geometry

3 things
things geometry atoms lone pairs

shape

example

• There are two molecular geometries:
– Trigonal planar, if there are no lone pairs
– Bent, if there is a lone pair.
•

3 sesuatu  trigonal planar 2 bentuk
– Trigonal planar  tiada PEB
– Bent  ada PEB

Molecular
Geometries
and Bonding

Lone pairs and Bond Angle
PEB dan sudut ikatan
• Lone pairs are physically larger than atoms.
Ukuran PEB lebih besar drpd atom

• Therefore, their repulsions are greater; this
tends to decrease bond angles in a
molecule.
Tolak-menolak PEB lebih besar  menurunkan
sudut ikatan

Molecular
Geometries
and Bonding

Multiple Bonds and
Bond •Angles
Double and triple bonds
place greater electron
density on one side of the

central atom than do
single bonds.
Ikatan rangkap dua dan tiga
meletakkan densitas elektron yg
lebih besar pada satu sisi atom
pusat drpd ikatan tunggal

• Therefore, they also affect
bond angles.
Ikatan rangkap dua dan tiga
berpengaruh tdp sudut ikatan
Molecular
Geometries
and Bonding

Tetrahedral geometry 4 things
Things geometry atoms lone pairs

•

shape

There are three molecular geometries:
4 sesuatu  tetrathedral  3 bentuk yg mungkin
– Tetrahedral, if no lone pairs (tiada PEB)
– Trigonal pyramidal if one is a lone pair ( 1 PEB)
– Bent if there are two lone pairs (2 PEB)

example

Molecular
Geometries
and Bonding

Trigonal Bipyramidal geometry
5 things
• There are two
distinct positions in
this geometry:
• 5 sesuatu  trigonal
bipyramidal  2
posisi yang berbeda:
– Axial
– Equatorial
Molecular
Geometries
and Bonding

Trigonal Bipyramidal geometry

Lower-energy conformations result from
having lone pairs in equatorial, rather than
Molecular
axial, positions in this geometry.
Geometries
PEB pada posisi equatorial  lebih stabil and Bonding

Trigonal Bipyramidal geometry
Things geometry atoms lone pairs shape

example

• There are four
distinct
molecular
geometries in
this domain:
4 bentuk yg
mungkin
– Trigonal
bipyramidal
– Seesaw
– T-shaped
– Linear

Molecular
Geometries
and Bonding

Octahedral geometry 6 things
Things geometry

•
•

atoms

lone
pairs

shape

example

All positions are equivalent in the octahedral domain.
There are three molecular geometries: 3 bentuk yg mungkin

Molecular
Geometries
and Bonding

Larger Molecules
In larger molecules, we talk
about the geometry about a
particular atom rather than
the geometry of the molecule
as a whole.
Dlm molekul yang lebih
besar  geometri atom
tertentu, bukan geometri
seluruh molekul

Molecular
Geometries
and Bonding

Larger Molecules
The structure of the
whole molecule is only
clear when we look at
the whole molecule.
Struktur molekul  jelas
jika melihat keseluruhan
molekul

But the geometry
about each atom still
follows the same rules!
Geometri tiap atom tetap
Molecular
Geometries
and Bonding

Polarity
• polar bonds versus polar
molecules.
Ikatan polar vs molekul
polar

We must think about the
molecule as a whole.
Pertimbangkan molekul
secara utuh
Molecular
Geometries
and Bonding

Polarity
By adding the individual
bond dipoles, one can
determine the overall
dipole moment for the
molecule.
Dipole tiap ikatan 
momen dipole total
dari molekul

Molecular
Geometries
and Bonding

Polarity
“The tractor pull”

Molecular
Geometries
and Bonding

Break....

Molecular
Geometries
and Bonding

Overlap and Bonding
tumpang tindih dan ikatan
• covalent bonds form when electrons are “shared.”
ikatan kovalen terbentuk ketika elektron dipakai-bersama (berbagi-pakai)

• But how, when the electrons are in these atomic orbitals?
Bgmn jika elektron berada dalam orbital atom?

Do atomic orbitals overlap?
Apakah orbitalnya saling tumpang-tindih?

• Yes.

Molecular
Geometries
and Bonding

Overlap and Bonding
• Increased overlap brings the
electrons and nuclei closer
together while simultaneously
decreasing electron-electron
repulsion.
Overlapping membuat
elektron&inti semakin dekat 
menurunkan tolak-menolak
elektron-elektron

• However, if atoms get too
close, the internuclear
repulsion greatly raises the
energy.
Atom terlalu dekat  tolakmenolak antar inti menjadi besar

Molecular
Geometries
and Bonding

Hybrid Orbitals

But how do you get tetrahedral, trigonal bipyramidal,
and other geometries when the atomic orbitals seem
to be at right angles from each other all the time?
Bgmn didapatkannya bentuk geometri molekul tsb?
Molecular
Geometries
and Bonding

Hybrid Orbitals
• Consider beryllium
(4Be):
– In its ground electronic
state, it would not be
able to form bonds
because it has no
singly-occupied orbitals.
Dlm kondisi dasar tdk
dpt berikatan, krn tdk
memiliki orbital yg berisi 1
elektron

Molecular
Geometries
and Bonding

Hybrid Orbitals
But if it absorbs the
small amount of
energy needed to
promote an electron
from the 2s to the 2p
orbital, it can form two
bonds.
Promosi 1 elektron dari
2s ke 2p
Molecular
Geometries
and Bonding

Hybrid Orbitals
• Mixing the s and p orbitals yields two degenerate
orbitals that are hybrids of the two orbitals.
Penggabungan orbital s dan p  orbital hibrid sp

– These sp hybrid orbitals have two lobes like a p orbital.
Orbital hibrid sp memiliki 2 lobe seperti orbital p

– One of the lobes is larger and more rounded as is the s
orbital.
Satu lobe besar dan satu lobe kecil (mirip orbital s)

Molecular
Geometries
and Bonding

Hybrid Orbitals
• These two degenerate orbitals would align
themselves 180 from each other.
Dua orbital tsb akan bersudut 180 satu sama lain

• This is consistent with the observed geometry of
beryllium compounds: linear.
Sesuai dgn hasl pengamatan geometri BeF 2
LINIER

Molecular
Geometries
and Bonding

Hybrid Orbitals

• With hybrid orbitals the orbital diagram for beryllium
would look like this.
• The sp orbitals are higher in energy than the 1s
orbital but lower than the 2p.
Energi orbital: 2p>sp>1s

Molecular
Geometries
and Bonding

Hybrid Orbitals
Using a similar model for (3B) boron leads to…

Molecular
Geometries
and Bonding

Hybrid Orbitals
…three degenerate sp2 orbitals.
.... Tiga orbital sp2 yang berenergi
sama besar

Molecular
Geometries
and Bonding

Hybrid Orbitals
With (6C)carbon we get…

Molecular
Geometries
and Bonding

Hybrid Orbitals
…four degenerate
sp3 orbitals.
...empat orbital sp3 yg
sama besar energinya

Molecular
Geometries
and Bonding

Hybrid Orbitals
For geometries involving expanded octets on
the central atom, we must use d orbitals in our
hybrids.
Utk geometri yg melibatkan >8 elektron pd atom pusat 
orbital d dilibatkan

Molecular
Geometries
and Bonding

Hybrid Orbitals
This leads to five degenerate
sp3d orbitals…
lima orbital sp3d

…or six degenerate sp3d2
orbitals.
... atau Enam orbital sp3d2
Molecular
Geometries
and Bonding

Hybrid
Orbitals
Once you know the
number of things
around an atom, you
know the
hybridization state of
the atom if you can
count letters up to six.
Mengetahui sesuatu di
sekitar atom  mengetahui
tingkat hibridisasinya
Molecular
Geometries
and Bonding

Valence Bond Theory
teori ikatan valensi
• Hybridization is a major player in this
approach to bonding.
Pendekatan menggunakan hibridisasi

• There are two ways orbitals can overlap
to form bonds between atoms.
Dua cara orbital saling tumpang tindih:
– Sigma (
– Phi ( )
Molecular
Geometries
and Bonding

Sigma () Bonds

• Sigma bonds are characterized by
– Head-to-head overlap.(tumpang tindih kepala-kepala)
– Cylindrical symmetry of electron density about the
internuclear axis. (densitas elektronnya simetris silindris
di sekitar sumbu antar inti)

Molecular
Geometries
and Bonding

Pi () Bonds
• Pi bonds are
characterized by
– Side-to-side overlap.
Timpang tindih
samping-samping

– Electron density
above and below the
internuclear axis.
(densitas elektron
atas & bawah sumbu
antar inti)

Molecular
Geometries
and Bonding

Single Bonds
Single bonds are always  bonds, because  overlap is
greater, resulting in a stronger bond and more energy
lowering.
Ikatan tunggal selalu sigma, overlap sigma lebih besar dan menghasilkan
ikatan yg lebih kuat dan berenergi rendah

Molecular
Geometries
and Bonding

Multiple Bonds
In a multiple bond one of the bonds is a  bond
and the rest are  bonds.
Ikatan rangkap  satu sigma, lainnya phi

Molecular
Geometries
and Bonding

Multiple Bonds
• Example: formaldehyde an
sp2 orbital on carbon
overlaps in  fashion with
the corresponding orbital on
the oxygen.
Orbital sp2 karbon overlap
dgn sp2 oksigen
sp2-sp2

• The unhybridized p orbitals
overlap in  fashion.
orbital p sisa karbon overlap
dgn p sisa oksigen
py - p y
Molecular
Geometries
and Bonding

Multiple Bonds
In triple bonds, as in
acetylene, two sp orbitals
form a  bond between
the carbons, and two
pairs of p orbitals overlap
in  fashion to form the
two  bonds.
sp-sp
py-py
pz-pz

Molecular
Geometries
and Bonding

Delocalized Electrons:
Resonance
When writing Lewis structures for species like
the nitrate ion, we draw resonance structures to
more accurately reflect the structure of the
molecule or ion.

+
-

+
-

¸

+
-

¸

¸

Molecular
Geometries
and Bonding

Delocalized Electrons:
Resonance
• each of the four atoms in the
nitrate ion has a p orbital.
Tiap atom dalam ion nitrat memiliki
orbital p

• The p orbitals on all three
oxygens overlap with the p orbital
on the central nitrogen.
Ion Nitrat

Tiap orbital p dari atom2 oksigen
overlap dngn orbital p dari nitrogen
Molecular
Geometries
and Bonding

Delocalized Electrons:
Resonance
This means the  electrons are
not localized between the
nitrogen and one of the
oxygens, but rather are
delocalized throughout the ion.
Elektron phi tdk terlokalisir di
antara N dan salah satu O saja
tetapi terdelokalisir ke seluruh
bagian ion
Molecular
Geometries
and Bonding

Resonance
The organic molecule
benzene has six 
bonds and a p orbital
on each carbon atom.
Bensen memiliki 6 ikatn
sigma dan 6 orbital phi

Molecular
Geometries
and Bonding

Resonance
• In reality the  electrons in benzene are not localized, but delocalized.
Elektron phi dlm bensen terdelokalisir

• The even distribution of the  electrons in benzene makes the
molecule unusually stable.
Membuat bensen STABIL

Molecular
Geometries
and Bonding

Valence bond theory
• Hybridization to explain geometry.
Hibridisasi menjelaskan geometri
• What orbitals are involved in multiple bonds?
Orbital apa yang terlibat dalam ikatan rangkap?

• Delocalization and resonance.
Delokalisasi dan resonansi

Molecular
Geometries
and Bonding

Teori Orbital Molekul

Molecular
Geometries
and Bonding

Teori Orbital Molekul

Molecular
Geometries
and Bonding

Molecular Orbital (MO) Theory
Valence bond theory works very
well for most observed properties
of ions and molecules, but there
are some concepts better
represented by molecular orbital
theory.
Teori ikatan valensi mampu
menerangkan dgn baik sifat2
yang teramati pada ion dan
molekul.. tetapi...
Beberapa konsep lebih
gamblang dijelaskan
menggunakan teori orbital
molekul

Molecular
Geometries
and Bonding

Molecular Orbital (MO) Theory
• In MO theory, we invoke
the wave nature of
electrons.
teori MO melibatkan sifat
gelombang dr elektron

• If waves interact
constructively, the
resulting orbital is lower in
energy: a bonding
molecular orbital.
Gelombang berinteraksi
konstruktif  orbital
ikatan

Molecular
Geometries
and Bonding

Constructive & Destructive Interference

Constructive Interference
Waves are “in phase.” By superposition, red + blue = green. If red
and blue each have amplitude A,
then green has amplitude 2A.

Destructive Interference
Waves are “out of phase.” By
superposition, red and blue
completely cancel each other
Molecular
out, if their amplitudes and
Geometries
frequencies are the same.and Bonding

Molecular Orbital (MO) Theory
If waves interact constructively, the
resulting orbital is lower in
energy: a bonding molecular
orbital.
Gelombang berinteraksi
konstruktif  orbital ikatan
If waves interact destructively, the
resulting orbital is higher in
energy: an antibonding
molecular orbital.
Gelombang berinteraksi destruktif
 orbital anti-ikatan
Molecular
Geometries
and Bonding

Molecular Orbital (MO) Theory

• Valence bond theory:
• atomic orbitals are mixed in
each individual atom before
bonding.

• Molecular orbital theory:
• no prebonding mixing.
Molecular orbitals are
computed after bonding.

Molecular
Geometries
and Bonding

MO Theory
• In H2 the two electrons go into
the bonding molecular orbital.
Dlm H2, dua elektron mengisi
orbital ikatan
• The bond order is one half the
difference between the number
of bonding and antibonding
electrons.
Orde ikatan =
½ (elektron dlm orbital
ikatan-elektron dlm orbital
anti-ikatan)
Molecular
Geometries
and Bonding

MO Theory
For hydrogen, with two
electrons in the bonding
MO and none in the
antibonding MO, the bond
order is
untuk H2 , orde ikatan =

1
(2 - 0) = 1
2
Molecular
Geometries
and Bonding

MO Theory
• In the case of He2,
the bond order
would be
1
(2 - 2) = 0
2
• Therefore, He2
does not exist.
Molecular
Geometries
and Bonding

Rules for making and filling
molecular orbitals
aturan dlm membuat dan mengisi orbital molekul
• 1. The number of MO’s equals the # of Atomic orbitals
jumlah MO = jumlah AO
• 2. The overlap of two atomic orbitals gives two molecular orbitals,
1 bonding, one antibonding
overlap dua AO menghasilkan dua orbital: ikatan & anti-ikatan
• 3. Atomic orbitals combine with other atomic orbitals of similar
energy.
AO bergabung dgn AO yang sama energinya
• 4. Degree of overlap matters. More overlap means bonding orbital
goes lower in E, antibonding orbital goes higher in E.
Ada tingkatan dlm overlapping. Orbital ikatan berenergi
rendah. Orbital anti-ikatan berenergi tinggi.
• 5. Each MO gets two electrons
setiap MO berisi dua elektron
• 6. Orbitals of the same energy get filled 1 electron at a time until
they are filled.

Orbital dari energi yang sama bisa diisi dn 1 elektron pada waktu sampai
Molecular
terpenuhi.

Geometries
and Bonding

MO Theory
• For atoms with both s and
p orbitals, there are two
types of interactions:
atom2 dng orbital s & p
memiliki dua interaksi
– The s and the p orbitals
that face each other
overlap in  fashion.
s &p overlap dlm pose
sigma
– The other two sets of p
orbitals overlap in 
fashion.

Molecular
Dua p overlap dlm pose
phi

Geometries
and Bonding

MO Theory

• The resulting MO diagram looks like this.
Molecular
• There are both  and  bonding molecular orbitals andGeometries
*
and Bonding
and * antibonding molecular orbitals.
*= anti ikatan

MO Theory

• The earlier p-block elements
in the second period have a
sizeable interaction between
the s and p orbitals.

Terdapat interaksi yg signifikan
antara orbital s & p untuk unsur2
blok dr periode kedua

• This flips the order of the 
and  molecular orbitals in
these elements.

Hal tsb membalikkan urutan
orbital sigma dan phi dari unsur
tsb

Molecular
Geometries
and Bonding

Second-Row MO Diagrams

Molecular
Geometries
and Bonding

Heterodiatomic molecules
CO has a triple bond

C

CO

Molecular
Geometries
and Bonding

Heterodiatomic molecules
NO is paramagnetic
radical

Molecular
Geometries
and Bonding

Why MO theory?
MO theory explains things that Valence
Bond theory does not.
1. Magnetism
2. Color of molecules
3. Excited states of molecules.

Molecular
Geometries
and Bonding

Magnetism
We learned that electrons have magnetic quantum
number ms “spin”.
Electrons have magnetic moment.
Electrons cause magnetism.

Three kinds of magnetism:
1. Diamagnetism
2. Paramagnetism
3. Ferromagnetism

Molecular
Geometries
and Bonding

Diamagnetic

Electrons all paired

Paramagnetic

Unpaired electrons
Molecular
Geometries
and Bonding

Oxygen O2 is Paramagnetic!
.. ..
O
.. O
..

Why?

Molecular
Geometries
and Bonding

MO to the rescue

Molecular
Geometries
and Bonding

Ferromagnetism
Like iron, pulled to a magnet.
Long range order of spins in material
S

N

Molecular
Geometries
and Bonding

MO theory and color

Remember, elements produced color because of electrons
Moving from higher to lower energy levels.

Molecular
Geometries
and Bonding

With MO theory, color of molecules is explained the same way

Conjugated polyenes have MO’s that give
rise to colors, energy is absorbed, electrons
go to higher energy levels.

Molecular
Geometries
and Bonding

How do we see color?

Isomerization
wiggles the rest of
the protein, sends
nerve signal

Rhodopsin

Molecular
Geometries
and Bonding




Molecular
Geometries
and Bonding

How does Color Vision work?
Each rhodopsin (Rod, Blue, Green, Red) protein exhibits a different wavelength 
maxima  as  a  result  of  11cis­retinal  binding  as  a  protonated  Schiff  base  (PSB) 
via a lysine residue.  It is these interactions that lead to color vision and allow us 
to see the whole visible spectrum.

11­cis­retinal : ~ 380 nm
11­cis­retinal SB : ~ 365 nm
N
H

11­cis­retinal PSB : ~ 440 nm
PSB in Blue Rhodopsin : ~ 410 nm

400 
nm

Wavelength 
(nm)

700 
nm

PSB in Green Rhodopsin : ~ 530 nm
Molecular
PSB in Red Rhodopsin : ~ 560 nm

Geometries
and Bonding
PSB in Rod Rhodopsin : ~ 500 nm

You can change the energy of
the MO’s of retinal by changing
the environment around the
molecule.

Molecular
Geometries
and Bonding