ENERGY BANDS

Question 1

What is the typical energy range for chemical bonds in ionic, covalent and metallic compounds? How large are the energies for van der Waals bond sand H-bonding?

Answer 1

Ionic: 400-7000 kJ/mol
Covalent: 200-1000 kJ/mol
Dipole: 40-400 kJ/mol
H-H bond: 10-40 kJ/mol
van der Waal: 1 kJ/mol

Question 2

What is the physical reason for reduction in the atomic size on moving from left to right in a period (of the periodic table)?

Answer 2

stronger effective nuclear charge.

Question 3

Describe three interactions involving antiparallel alignment of electrons.

Answer 3

chemical bond, cooper pair (superconductivity), antiferromagnetic coupling

Question 4

Make a sketch and illustrate the pi bonding and antibonding situation for two p-orbitals.

Answer 4

two cases: overlap between in phase and overlap between out of phase.

Question 5

Can you explain why polyacetylene is semiconducting and not metallic?

Answer 5

Because its a chain which can be considered as a 1D chain of orbitals with distortion. Then we get peierls distortion, which says that we get a band gap, hence semiconducting.

Question 6

Explain what type of information is provided by “COOP”.

Answer 6

All states are taken into account by the Mulliken overlap population, so 1-2 case, 1-3 case, 1-4 case etc..

Question 7

Explain what type of information is provided by “ELF”.

Answer 7

Electron localization function shows where the electron pairs are most likely to be.