SMU - Hybridisation

Question 1

what is hybridisaition

Answer 1

• essentially a mixture of atomic orbitals
• when different atomic orbitals of same or nearly same energy combine together to form new, energetically favourable orbital arrangements.

Question 2

How does sp3 hybridisation occur and why.
use methane as an example

Answer 2

so carbon has 6 electrons, and are aranged like this -
1s - 2 e-
2s - 2 e-
2p - 2 e-
Looking at this arrangement, we can see only 2 valence electrons in the outer sheel or higher energy level, the 2px and 2py electrons.

so to correct this, a 2s e- is prmotoed into the 2pz energy level, this is the exited state. forming a hybridised second energy orbital.

• so now 4 electrons are in the 2nd evergy level, 1 from 2s and 3 from 2p, forming a sp3 hybridised orbital.
• all the electrons here have equal energy, which is slightly less than that of the 2p orbtial
  (cos the s(lower) and p(higher) anre combined.

allowing the formation of 4 equvilent covalent bonds to form in methane.

Question 3

what is the bond angle of a molecule with sp3 hybridisation

Answer 3

109.5 degrees

Question 4

what geomtrical shape does sp3 hybridised molecules form

Answer 4

tetraheadral

Question 5

why do we study hybiridisation, what does it allow us to see.
2 reasons

Answer 5

1. molecular geometry (shapes of molecules and all that)
2. bonding of orbitals (if a sigma or pi bond form)

Question 6

does hybridisation occur in all molecules,
if yes, then why and how
if no, then give examples

Answer 6

No, for example in H2, HCl and H2S (hydrogen sulfide)

Question 7

define degenerate orbitals, give and example.

Answer 7

orbitals having the same energy. like in methane, all covalent bond are in the same energy level.

Question 8

what are unhybrid orbitals, and in what hybridisation can they be found in.

Answer 8

they are electrons in orbitals, that dont mix with another orbital.
eg - in ethene, only 2 electrons in the 2p orbital, form a hybrid with the 2s electron. and the last of those forms the pi bond

Question 9

what bond do electrons in unhybrid and hybrid orbitals form.

Answer 9

hybrid - sigma bonds
unhybrid - pi bonds

Question 10

whatbond angle and geometry would a molecule showing sp2 hybridisation show

Answer 10

120 degress, triganol planar.

Question 11

give an example of an sp hybridised orbital.
- their bond angle
- their geometry

Answer 11

eg - ethyne
angle - 180 degress
geometry - linear

Question 12

which bond is stronger, the sigma or pi

Answer 12

sigma bond

Question 13

how are the pi and sigma bond arranged in a c=c molecule.

how do these arrangements affect c=c in terms of rotation

Answer 13

the sigma bond forms first, with the head on overlap, along the same axis.
the pi bond forms on top if this intial sigma bond, between the parallel overlapping p orbitals.

the pi bond, only further decreases the disteance between the c=c, but it does restric the rotation of the c=c.
which enables them to take part in steriochemistry, to form E/Z- isomers.

Question 14

how to work out the steric number of a molecule,

give example with methane

Answer 14

steric number = no. of sigma bonds + no. of lone pairs.

methane -
4 sigma bonds + 0 lone pairs

SN = 4