f block

Question 1

why are f block elements not really effected by crystal field theory?

Answer 1

orbitals tend to be core like and unavailable therefore are largely unaffected by the ligands attached to them

Question 2

what is the bonding like between f block elements and ligands?

Answer 2

no overlap of orbitals between f and the ligands thus the f orbitals do not participate in bonding

Question 3

what determines the structure of the metal complexes in lanthanides? what is the bonding between lanthanides and ligands?

Answer 3

sterics of the ligands
-> not effected as much by orientation of orbitals due to its core like (spherical) structure

electrostatics (negative electrons from the ligands and the positive metal ion)

Question 4

can you measure the NMR of lanthanides and why?

Answer 4

difficult because most of them are paramagnetic

it is difficult to record the NMR of paramagnetic species due to:
Broadened NMR signals: In paramagnetic species, unpaired electrons create additional magnetic fields that can influence the local electronic environment of nearby atomic nuclei. This results in a broadening of the NMR signals, making it difficult to obtain well-resolved peaks. The broadening effect can obscure the fine details of the NMR spectrum and make it harder to interpret.

Relaxation effects: Paramagnetic species often exhibit faster nuclear relaxation times compared to diamagnetic species (substances without unpaired electrons). The presence of unpaired electrons enhances the relaxation processes, reducing the signal intensity and making it more challenging to detect and analyze the NMR signals.

Line shape distortions: The broadening and relaxation effects mentioned above can result in distorted line shapes in the NMR spectrum. The lines may become asymmetric, overlapping, or featureless, making it difficult to extract meaningful information about the molecule’s structure and dynamics.

Paramagnetic interference: The paramagnetic properties of the species being studied can interfere with the magnetic field homogeneity required for precise NMR measurements. The presence of paramagnetic species in the vicinity can lead to field distortions and cause artifacts in the NMR spectrum.

Question 5

what are the 3 elements that like the 2+ oxidation state for lanthanides?

Answer 5

Eu, Sm, Yb

due to almost half filled, half filled and full orbital

Question 6

which element prefers to be in the 4+ oxidation state in the lanthanides and why?

Answer 6

Ce due to achieving Xenon configuration which is highly stable

Question 7

which oxidation state is most common with lanthanides and why?

Answer 7

3+ oxidation state due to having the most thermodynamic stability

the 3+ lanthanide ions have a relatively high charge density and can readily form stable complexes due to their favorable size and electronic properties.

Question 8

what are the 2 anomalies in the metallic radii of lanthanides and why?

Answer 8

Eu and Yb both prefer a 2+ oxidation state which is larger than the 3+ oxidation state for the rest of the lanthanides (thus appear to have a larger metallic radii)

Question 9

why do f-block elements have large coordination numbers?

Answer 9

1. larger size means that they can accommodate more ligands
2. ionic bonding is non directional (lack of need for orbital overlap) means that more likely to have more ligands around f block ion

Question 10

what is the gadolinium break and what is the cause of this?

Answer 10

trend does not increase in stability due to the change in water coordination from 9->8 (logK decreases because there is a slight loss of entropic drive)

Question 11

what are the significant differences between colouring/intensity of lanthanide and transition metal complexes?

Answer 11

4f does not react strongly with ligands thus crystal field effects and vibronic coupling is insignificant (no covalency for lanthanides)

less intense colouring for lanthanides (lower energy transitions and ionic point charge bonding means that they are normally laporte forbidden)

Question 12

are f-f absorption bands sharper or broader than d-d? why?

are they dependent on its environment?

Answer 12

sharper because for d-d there is vibronic coupling which involves changing electronic and vibrational states leading to a wider range of absorption values

for f block it is independent of gas/solution/solid but not for d block because the solution can bind to the metal as well

Question 13

which electrons are lost first in d complexes?

Answer 13

s electrons are lost before the d electrons

Question 14

what are the additional differences between the 4f and 5f orbitals?

Answer 14

5f has an additional radial node

5f also has a greater extension thus have a greater covalent contribution to bonding

Question 15

what are uses of uranium and why?

Answer 15

nuclear power, nuclear weapons

submarines (no refuelling requires)

ice breaking vessels

Question 16

uses of plutonium?

Answer 16

superfuel for nuclear reactors but very expensive

Question 17

what is the general principle of nuclear fission?

Answer 17

large nucleus -> 2 smaller nuclei + neutrons(s) that collide with other nuclei to continue reaction

chain reaction!

Question 18

how is U238 and U235 formed?

Answer 18

by making UF6 -> uranium enrichment process

1. U-F bonds are strong enough for U to want to form 6+ ion
2. F only has 1 isotope so the different forms of U can be separated

Question 19

what are the 2 different methods used to separate U238 and U235?

Answer 19

Gaseous diffusion: lighter molecule travels more quickly and diffuses through a membrane (separation)

Gas centrifuge: rotating (very fast spinning) cylinder makes heavier isotope on the outside the the lighter isotope closer to the center (less energy intensive)

Question 20

what is alpha radiation and how does it effect the atomic mass and atomic number? what is its penetrating ability?

Answer 20

emission of alpha particle (helium like) and -4 for atomic mass and -2 for atomic number

stopped quite easily (air or sheet of paper)

Question 21

what is beta radiation?

Answer 21

neutron transforms into a proton and electron so +1 for atomic number then that electron is yeeted out

(stopped by few mm sheet of aluminium)

Question 22

what is gamma radiation?

Answer 22

radiation that is emitted alongside beta decay, identity of an element remains unchanged

most penetrating thus lead shielding is required to reduce its intensity

Question 23

what is the effect that dominates in the magnetism of f block elements and why?

Answer 23

spin-orbit coupling as the orbitals have more interactions with the electrons as they are less influenced by the ligands

Question 24

why are actinides more magnetic than lanthanides?

Answer 24

larger extension of 5f orbitals means that it allows for much stronger interactions with neighbouring spin active species