Energy Bands Flashcards
What is the typical energy range for chemical bonds in ionic, covalent and metallic compounds?
How large are the energies for can der Waals bonds and H-bonding?
- Covalent: 200-350 kJ/mol
- Ionic: 250 kJ/mol
- Metallic: 200 kJ/mol
- vdW:
- H-bonding: 20 kJ/mol
What is the physical reason for reduction in the atomic size on moving from left to right in a period?
fsd
Describe three interactions involving antiparallel alignment of electrons.
nf
Make a sketch and illustrate the pi-bonding and anti-bonding situation for two p-orbitals
pls draw
Draw a 1D chain of atoms. Illustrate the variation in the wave function for k = 0 and pi/2
pls draw
Draw the energy versus k curve (band structure) for “polyhydrgoen” - a 1D chain of atoms.
pls draw
Imagine that we instead of having the 1D chain of s-orbitals of H, did have a 1D chain of p-orbitals with s overlap. Draw the band structure (energy dispersion curve) and explain why it is different from the situation with H-atoms.
pls draw
Explain what you understand with the k-vector
k is a node counter, has directionality, a vector in 3D
k = 0: All orbitals unchanged in sign
k = pi/a: Every second atom (unit cell) has inversed their orbital sign (a = lattice constant)
What is density of stated (DOS) and how does it vary for the energy band (dispersion) for the “polyhydrogen” chain?
Fermi-level: Highest O
How does the degree of dispersion vary with the strength of the interaction (bonding) between the involved atoms/orbitals?
A sharp dispersion indicate stronger bonds.
Can you explain why polyacetylene is semiconductnig and not metallic?
yes
Explain what type of information if provided by “COOP”.
(Crystal Orbital Overlap Population)
Explain what type of information is provided by “ELF”.
(Electron localization function)
Probability of finding another electron in a region where there already is located an electron from before.
Between 0 and 1
Consider the energy bands of graphene. Explain why it is a metal. Is there a high DOS at the Fermi level? From the dispersion curve, what type of orbitals are involved in the bands at the Fermi level?
fnds
Give some examples of 2D materials. Consider MoS_2. There exists two polymorphs; hexagonal and tetragonal. Explain why their electronic properties are very different.
https://en.wikipedia.org/wiki/Crystal_field_theory (nice energy-figures)
