Lecture One

Question 1

What is the common oxidation state of the lanthanides?why are their properties similar?

Answer 1

+3 , properties are similar due to contracted 4f orbitals, making their discovery and separation hard.

Question 2

Relative abundance of lanthanides

Where are they found?

Answer 2

• not rare
• found in minerals such as xenotime, monazite (LnPO4) and bastnaesite (LNCO3F).

Bastnaesite and monazite contain more late than early lanthanides.

Eu 2+ co exists in minerals with Sr 2+ and Ba 2+ with bastnasite and monazite being deficient

Promethium is radioactive and therefore decays easily and is rare

Question 3

Describe the 4f orbitals

Answer 3

• there are 7 4f orbitals
• no radial nodes and 3 angular nodes
• Ungerade symmetry

Question 4

How are the 4f orbitals “core like”?

Answer 4

• they penetrate the [Xe] core and are held close to the nucleus
• do not extend beyond the filled 5d and 6s orbitals

Question 5

How do the 4f orbitals affect bonding?

Answer 5

• The orbitals are screened from the ligand environment and there is o crystal field interaction
• bonding in lanthanides is highly ionic with fast ligand exchange

Question 6

How do the 4f orbitals affect magnetism and spectroscopy?

Answer 6

Spectroscopic and magnetic effects are almost independent of environment due to small CFSE

Question 7

The cubic set of 4f orbitals:

Answer 7

Contains two shapes, 4fz3, 4fx3 4fy3 these orbitals have one planar node and two conical nodes. The 4fxyz orbital has eight lobes each pointing to the corners of a cube whose faces define the direction of the x-,y- and z-axes. The 4fz(x2-y2), 4fy(z2-x2) and 4fx(z2-y2) are related to the 4fxyz by a 45o rotation about the z-, y- and x-axes respectively – these orbitals have three planar nodes.

Question 8

The general set of 4f orbitals

Answer 8

Consists of 4fz3, 4fxyz and 4fz(x2-y2) from the cubic set along with 4fxz2 and 4fyz2 (related by a 90o rotation about the z-axis) and 4fx(x2-3y2) and 4fy(3x2-y2) (related by a 90o rotation about the z-axis).

Question 9

why does Ln 3+ dominate lanthanide chemistry?

Answer 9

The fourth ionisation energy is significantly larger than the first three ionization energies. In most cases

• the extra energy to remove the 4th electron cannot be compensated for by bond formation.

Question 10

What electrons are lost first in lanthanide ionisation?

Answer 10

As the 4f orbitals are contracted, the 6s and then 5f electrons are lost

Question 11

What elements have the most 2+ chemistry?

What effect does it have on physical properties?

Answer 11

Eu,Yb and Sm have appreciable 2+ chemistry. Eu 2+ and Yb 2+ have half/filled subshells and Sm2+ maximises exchange energy.

• affects ionic radii and means Eu and Yb act like heavy group 2 elements

Question 12

Which elements have the most 4+ chemistry

Answer 12

Ce and Tb

Ce 4+ is accessible due to due to the high energy of the 4f orbitals at the beginning of the series and is useful as an oxidising agent

Question 13

Explain the Lanthanide Contraction

Answer 13

• metallic and ionic radii decrease across the series
• 4f orbitals do not screen electrons from nuclear charge, resulting in a smaller radii
• 4d to 5d radii are similar
• Slight increase in metallic radii for Eu and Yb as they are (2+)