Molecular Orbitals

Question 1

What does covalent bonding between atoms involve?

Answer 1

the overlap of atomic orbitals (s,p orbtials) to form molecular orbitals (π σ)

Question 2

How are molecular orbitals formed?

Answer 2

By the linear combination of atomic orbitals

Question 3

What maximum number of electrons can each molecular orbital hold?

Answer 3

2

Question 4

What are the two types of molecular orbitals?

Answer 4

bonding and antibonding

Question 5

What are molecular orbitals formed by the overlap of s orbitals denoted with?

Answer 5

sigma (σ)

Question 6

Why is it called a bonding molecular orbital?

Answer 6

the electrons in this orbital spend most of their time in the region directly between the two nuclei

Question 7

Why is it called a σ molecular orbital?

Answer 7

it looks like an s orbital when viewed along the bond axis

Question 8

How is a bonding molecular orbital made?

Answer 8

by adding the mathematical functions for the atomic orbitals that come together to form the molecule

Question 9

How is an antibonding molecular orbital made?

Answer 9

by subtracting one functiokn from the other

Question 10

Why is it called an antibonding molecular orbital?

Answer 10

the electrons spend most of their time away from the region between the two nuceli.

Question 11

What is an antibinding molecular orbital denoted with?

Answer 11

σ*

Question 12

How are electrons added to molecular orbitals?

Answer 12

one at a time, starting with the lowest energy molecular orbital

Question 13

In terms of a H2 molecule and its molecular orbital diagram, talk about its stability.

Answer 13

The diagram suggests that the energy of a H2 molecule is lower than that of the H atoms. As a result, the H2 molecule is more stable than a pair of isolated H atoms.

Question 14

Give the 3 possible orbital combinations that form σ bonds.

Answer 14

1. s orbital + s orbital
2. s orbital + p orbital
3. p-orbital + p orbital (‘head-on’ overlap)

Question 15

How are π bonds formed?

Answer 15

by the lateral overlap of p orbitals

Question 16

Why are they called π molecular orbitals?

Answer 16

They look like p orbitals when viewed along the line of the bond

Question 17

When carbon forms bonds, what happens to one of the 2s electrons?

Answer 17

it is promoted to a higher energy 2p orbital

Question 18

When carbon forms bonds, what happens to the 2s and three 2p orbitals?

Answer 18

they combine to make 4 equivalent orbitals called sp3 hybrid orbitals

Question 19

How many electrons does each sp3 hybrid orbital hold?

Answer 19

1

Question 20

What arrangement do the 4 sp3 hybrid orbitals take up?

Answer 20

tetrahedral

Question 21

For methane, what does each sp3 hybrid orbital on carbon do?

Answer 21

overlap with a 1s orbital of H to give 4 equivelant sigma (σ) bonds

Question 22

What are all 7 of the bonds in ethane?

Answer 22

σ bonds

Question 23

What are σ bonds found in?

Answer 23

all saturated molecules

Question 24

What is sp3 hybridisation found in?

Answer 24

all saturated molecules

Question 25

For bonding in alkenes, what kind of hybridisation occurs?

Answer 25

sp2 hybridisation

Question 26

Describe sp2 hybridisation.

Answer 26

It is the combination of the 2s orbital with 2 2p orbitals giving three equivelent sp2 hybrid orbitals

Question 27

What arrangement do the 3 sp2 hybrid orbitals adopt?

Answer 27

trigonal planar

Question 28

How does the unhybridised p-orbital sit?

Answer 28

sits at 90' to the planar structure

Question 29

Describe what happens to 2 sp2 hybrid orbitals in ethene?

Answer 29

they overlap to form a σ bond

Question 30

Describe what happens to the p orbitals on adjacent C atoms in ethene?

Answer 30

they overlap to form a π bond

Question 31

In ethene, what does the double bond consist of?

Answer 31

a σ and a π bond

Question 32

What do all double bonded C atoms show?

Answer 32

sp2 hybridisation

Question 33

Why are π bonds weaker than σ bonds?

Answer 33

the electrons in the bond are not localised between the nuclei

Question 34

What will the shape of the molecular orbital formed from overlapping atomic orbitals govern?

Answer 34

the type of intermolecular bonding that is observed

Question 35

Non-polar/ pure covalent bonds are formed between two atoms of the same element, or two atomd with a very low difference in electronegativities. Describe what effect this has on the molecular orbitals.

Answer 35

The molecular orbital formed from overlapping atomic orbitals is symmetrical around a mid-point where the bonding electrons are most likely to be found

Question 36

For when there is a large difference in electronegativities, describe the shape of the bonding molecular orbital.

Answer 36

asymmetrical