What is Hybridization? Used to explain some of the shapes of molecules in VSEPR Theory ( Valence...

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.

HybridisationThe shapes of the atomic orbitals involved can not explain the bonding observed in compounds such as alkanes.

x

zy

x

zy

x

zy

x

zy

x

zy

1s orbital 2s orbital

2px orbital 2py orbital 2pz orbital

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)

Incr

easi

ng e

nerg

y

2s

2p

hybridised orbitals

The hybrid orbitals formed from one s orbital and

three p orbitals are called sp3 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°.

an sp3 hybridised orbital

The sp3 orbitals are all half-filled orbitals.

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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.

C

H

H

H

H

Carbon-to-carbon single bonds in alkanes result from overlapping sp3 orbitals forming σ bonds.

H

H

H

C C

H

H

H

σ bond

Carbon-to-carbon single bonds in alkanes result from overlapping sp3 orbitals forming σ bonds.

H

H

H

C C

H

H

H

σ bond

σ bonds are covalent bonds

As with alkanes, an electron from the 2s shell is promoted to the empty 2p orbital.

Incr

easi

ng e

nerg

y

2s

2p

hybridised orbitals

The hybrid orbitals formed from one s orbital and two p orbitals are called sp2 orbitals.

single unhybridised 2p orbital

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.

Incr

easi

ng e

nerg

y

2s

2p

hybridised orbitals

The hybrid orbitals formed from one s orbital and two p orbitals are called sp2 orbitals.

single unhybridised 2p orbital

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26

When an s and two p orbitals are mixed to form a set of three sp2 orbitals, one p orbital remains unchanged

and is perpendicular to the plane of the hybrid orbitals.

remaining p orbitals from sp or sp2

s bond

formation of p bond

Planar molecule (each carbon is trigonal planar) with p cloud above and below the plane

p bond hinders rotation about the carbon-to-carbon bond

.

Incr

easi

ng e

nerg

y

2s

2p

hybridised two orbitals

The hybrid orbitals formed from two s orbital and two p orbitals are called sp orbitals.

2 unhybridised 2p orbital

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33

The orbitals of an sp hybridized carbon atom.

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 - sigma bond

• Double bond – sigma bond + pi bond

• Triple bond – sigma bond + pi bond + pi bond

end-to-end

side-to-side

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.

LecturePLUS Timberlake 45

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

Neutral atoms have the same number of protons and electrons.

Ions are charged atoms.cations – have more protons than electrons and are positively chargedanions – have more electrons than protons and are negatively charged

48

Chemical BondsMolecules 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.

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 ForcesDipole-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:

1 2 3 4

25% 25%25%25%

1. Between atoms.2. Between

molecules.3. Between cells4. Between any

particles.

Hydrogen bonding is:

1 2 3

33% 33%33%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.

Here, sugar (a polar substance) is in solution with water (also polar). Mark where the hydrogen bonds will form.