Orbital Hybridisation & VSEPR Learning Goals Students will be able to predict the hybridization in a variety of compounds using Lewis Structures & energy level diagrams Students will be able to use VSEPR to predict the hybridisation in a compound

Do your energy level diagrams make sense for the bonding you see in your compound?

AgreesDisagrees

The Lewis structure for methane (CH ₄ ) is: Based on the VSEPR model, the shape is tetrahedral. The energy level diagram for carbon is should form  bonds to only two hydrogen atoms How do you get four bonds at 109° and equal bond length from two unpaired electrons in p orbitals at 90°?

Key points re. molecular orbital's The locations of the electrons are described The locations of the electrons are described by atomic orbitals. by atomic orbitals. A given orbital can contain only 2 electrons. (Pauli exclusion principle.) Atomic orbitals on different atoms will can combine to give molecular orbitals, but only if their symmetry matches. Each orbital has an associated energy and electrons will occupy the lowest energy orbitals first. good  bond bad – wrong symmetry No bonding! No bonding!

Potential Energy Hybridisation = mixing of atomic orbitals to form new, identical orbitals s p sp³ WRITEDOWN

Hybridization of Orbitals Animation DRxS6khttps:// DRxS6k ssentialchemistry/flash/hybrv18.swfhttp:// ssentialchemistry/flash/hybrv18.swf Crash Course – UYIhttps:// UYI

Hybridized Carbon Orbitals The four sp 3 orbitals are arranged in a tetrahedral shape. Each hybrid sp 3 orbital contains one electron and is available to bond with another atom. So what happens in methane? When VB theory is combined with orbital hybridization, the result is a molecule that matches the shape and bond angles that are both experimentally observed and predicted by VSEPR

molecular orbitals. a C-C bond Csp 3 A molecular orbital (σ bond) with a pair of electrons Unstable: high energy! stable: lower energy! Two hybrid orbital's each have only 1 electron. This is a high energy situation: They combine to form a more stable situation:

Methane Four hydrogen atoms, each having an s orbital, overlap with each of the sp 3 orbitals. Each of these bonds is called a σ (sigma) bond o Whenever an atom is surrounded by four effective electron pairs, sp 3 hybrid orbitals are required. WRITEDOWN σ bond

You try it! Eg. 2 SiCl 4

What about BH 3 ? Eg. 3

BeCl 2

What about ethene? π (pi bond) A covalent bond formed by the parallel (side by side) overlap of two p orbitals.

C 2 H 4 H 2 C=CH 2 planar bond angles: close to 120° bond distances: C—H = 110 pm C=C = 134 pm Structure of Ethylene

Ethylene (Ethene) C 2 H 4 Each carbon atom forms: –three hybrid sp 2 orbitals that lie on the same plane at 120 o –and a third p orbital that is lying perpendicular to the plane

Ethylene (Ethene) C 2 H 4

Ethylene (Ethene) C 2 H 4

The double bond between the two carbon atoms is made up of a sigma bond and a pi bond. The pi bond is made up of the parallel overlap of the p orbitals. The sigma bond is made up of the end to end overlap of the sp 2 orbitals. Ethene (Ethylene), C 2 H 4

Double Bond A double bond is made up of a sigma bond and a pi bond.

Kind of Bond orbital hybridization single sp 3 double sp 2 triple ???? Can you recognize a pattern?

Acetylene (Ethyne), C 2 H 2 The carbon atoms forms: –two hybrid sp orbitals –two p orbitals.

Acetylene (Ethyne), C 2 H 2

Triple Bond Is made up of a sigma bond and two pi bonds.

Test Your Skill Identify the hybrid orbitals on the central atoms in SiH 4 and HCN.

s + p x = 2 sp orbitals P y orbital P z orbital sp hybrids only use 1 p orbital, the others are left unused and can so form 2 π bonds

C N

CN

CN

CN

CN H

VSEPR shape Bonding hybrid orbitals tetrahedral trigonal planar linear sp 3 sp 2 sp

sp hybrid orbital angle 180° sp sp pzpzpzpz pypypypy2s 2p z 2p x 2p y

sp 2 2s 2p z 2p x 2p y hybrid orbital angle 120° pzpzpzpz

sp 3 2s 2p z 2p x 2p y hybrid orbital angle 109.5°

Methane sp 3 H H C H H H C sp3 -H s