Transcript Slayt 1 - Near East University

What is Hybridization?
• Used to explain some of the shapes of
molecules in VSEPR Theory
( Valence shell electron pair repulsion)
What is Hybridization?
• Used to explain some of the shapes of
molecules in VSEPR Theory
( Valence shell electron pair repulsion)
• Hybridization Theory says that atoms boned
molecules will undergo structural changes in
their valence level atomic orbitals.
What is Hybridization?
• Used to explain some of the shapes of
molecules in VSEPR Theory
( Valence shell electron pair repulsion)
• Hybridization Theory says that atoms boned
molecules will undergo structural changes in
their valence level atomic orbitals.
• The atomic orbitals are converted into a new
set of orbitals called Hybrid Orbitals.
• The Hybrid Orbitals will have some
characteristics of the original atomic orbitals,
but differ somewhat in shape.
Hybridisation
The shapes of the atomic orbitals involved can
not explain the bonding observed in compounds
such as alkanes.
z
z
2px orbital
1s orbital
z
y
y
2s orbital
z
y
y
2py orbital
z
2pz orbital
y
sp3 hybridized
• In order to produce four identical orbitals
it is necessary to hybridize four atomic
orbitals.
sp3 hybridized
• In order to produce four identical orbitals
it is necessary to hybridize four atomic
orbitals.
• The Carbon atom has four valence atomic
orbitals, one s orbital and three p orbitals.
sp3 hybridized
• In order to produce four identical orbitals
it is necessary to hybridize four atomic
orbitals.
• The Carbon atom has four valence atomic
orbitals, one s orbital and three p orbitals.
• When these orbitals are hybridized, they
will produce four identical hybrid
orbitals.
• The new orbitals are called sp3 hybrids.
That the 2s and 2p orbitals of carbon atoms combine
(or mix) to form four degenerate orbitals (i.e. orbitals
of equal energy)
Increasing energy
2p
hybridised orbitals
2s
The hybrid orbitals formed
from one s orbital and
three p orbitals are called
sp3 orbitals.
an sp3 hybridised orbital
The sp3 orbitals are all half-filled orbitals.
Since electrons repel each
other, the four sp3 hybridised
orbitals surrounding a central
carbon atom
result in a familiar tetrahedral
shape,
with a maximum possible
angle between each orbital of
109.5°.
Copyright©2000 by Houghton Mifflin
Company. All rights reserved.
15
hybrid orbitals
formation of s bond
In methane, all four hybrid orbitals are used to
form σ bonds between the central carbon atom
and hydrogen atoms.
H
C
H
H
H
Carbon-to-carbon single bonds in alkanes result
from overlapping sp3 orbitals forming σ bonds.
H
H
C
C
H
H
σ bond
H
H
Carbon-to-carbon single bonds in alkanes result
from overlapping sp3 orbitals forming σ bonds.
σ bonds are covalent bonds
H
H
C
C
H
H
σ bond
H
H
As with alkanes, an electron from the 2s shell is
promoted to the empty 2p orbital.
single unhybridised 2p
orbital
Increasing energy
2p
hybridised orbitals
2s
The hybrid orbitals formed from one s
orbital and two p orbitals are called
sp2 orbitals.
As with alkanes, an electron from the 2s shell is
promoted to the empty 2p orbital.
This results in the formation of three hybrid orbitals, with
one remaining unhybridised 2p orbital.
single unhybridised 2p
orbital
Increasing energy
2p
hybridised orbitals
2s
The hybrid orbitals formed from one s
orbital and two p orbitals are called
sp2 orbitals.
When an s and two p orbitals are mixed to form a set
2
of three sp orbitals, one p orbital remains unchanged
and is perpendicular to the plane of the hybrid
orbitals.
Copyright©2000 by Houghton Mifflin
Company. All rights reserved.
26
s bond
remaining p orbitals from sp or sp2
p bond hinders rotation
about the carbon-to-carbon
bond
Planar molecule (each carbon is
trigonal planar) with p cloud
above and below the plane
formation of p bond
.
2 unhybridised 2p orbital
Increasing energy
2p
hybridised two orbitals
2s
The hybrid orbitals formed from two s
orbital and two p orbitals are called
sp orbitals.
The orbitals of an sp hybridized
carbon atom.
Copyright©2000 by Houghton Mifflin
Company. All rights reserved.
33
Sigma and Pi Bonds
• The primary bond used to connect two
atoms to each other is the sigma bond
(σ).
• Any additional bonds between two
atoms will be pi bonds (p).
• The sigma bond is the stronger of the
two types because of its effective use of
areas of maximum electron density.
Sigma and Pi Bonds
• The pi bonds are weaker and more
vulnerable to chemical attacks.
• This is primarily because pi bonds
locate maximum electron density
between the bonding nuclei but off to
the sides a little bit.
• A single bond is always a sigma
bond.
• A double bond is a sigma bond and a
pi bond.
• A triple bond is a sigma bond and
two pi bonds.
Bond formation from hybridization
• Single bond
end-to-end
- sigma bond
side-to-side
• Double bond
– sigma bond + pi bond
• Triple bond
– sigma bond + pi bond + pi bond
Figure 11.4
The sp3 hybrid orbitals in CH4.
Figure 11.5
The sp3 hybrid orbitals in NH3.
Figure 11.5
(continued)
The sp3 hybrid orbitals in H2O.
Why an atom make sigma or pi bond?
Octet rule
• The octet rule states that atoms are most stable
when they have a full shell of electrons in the
outside electron shell.
• The first shell has only two electrons in a single s
subshell. (Heliuman inert element)
• All the other shells have an s and a p subshell,
giving them at least eight electrons on the
outside.
• The s and p subshells often are the only valence
electrons, thus the octet rule is named for the
eight s and p electrons
Octet Rule
An octet in the outer shell makes atoms
stable
Electrons are lost, gained or shared to
form an octet.
Unpaired valence electrons strongly
influence bonding
Valence shells
• The valence shell is the outermost
shell of an atom.
• It is usually said that the electrons in
this shell make up its valance
electrons.
• This electrons that determine how the
atom behaves in chemical reactions.
Valence Electrons
 Electrons in the highest (outer) electron level
 Have most contact with other atoms
 Known as valence electrons
 Outer shells of noble gases contain 8 valence
electrons (except He = 2)
Example:
Ne
2, 8
Ar
2, 8, 8
LecturePLUS Timberlake
45
Neutral atoms have the
same number of protons
and electrons.
Ions are charged atoms.
cations – have more
protons than electrons
and are positively charged
anions – have more
electrons than protons
and are negatively
charged
Chemical Bonds
Molecules are groups of atoms held
together in a stable association.
Compounds are molecules containing
more than one type of element.
Atoms are held together in molecules or
compounds by chemical bonds.
48
Ionic bonding
• Ionic Bonding : Ionic bonds are formed when
there is a complete transfer of electrons from
one atom to another,
• resulting in two ions, one positively charged
and the other negatively charged.
– Some atoms gain electrons to become anions
– Others lose electrons to become cations
– Ions are attracted by their opposing charges
– Electrical Neutrality Maintained
Ionic Bonding
Covalent bonding
• Covalent bonding is when atoms share their
valence electrons in order to have 8 in their
outer shells.
• This bonding does not form ions.
• Such bonds lead to stable molecules if they
share electrons in such a way as to create a
noble gas configuration for each atom.
• Each atom donates one electron to form a
single covalent bond.
Chemical Bonds
Covalent Bonding
Polar bonding between atoms produces a
polar molecule, which has areas with slightly
positive or slightly negative charges.
Here, sugar (a polar substance) is in
solution with water (also polar). Mark
where the hydrogen bonds will form.
Nonpolar (ancharged) covalent bond
Types of Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
Hydrogen Bond (strongest)
•The hydrogen bond is a special dipole-dipole interaction
between the hydrogen atom in a polar N-H, O-H, or F-H
bond and an electronegative O, N, or F atom.
•IT IS NOT A BOND.
Hydrogen bonding occurs:
25%
25%
25%
25%
1. Between atoms.
2. Between
molecules.
3. Between cells
4. Between any
particles.
1
2
3
4
Hydrogen bonding is:
1. Strong and difficult
to break, like polar
covalent bonding.
2. A strong attraction
between charged
ions, like ionic
bonding.
3. A weak attraction
between polar
molecules.
33%
1
33%
2
33%
3
Here, sugar (a polar substance) is in
solution with water (also polar).
Mark where the hydrogen bonds will form.