1: Intro to Lanthanides

Question 1

What are the Lanthanides?

Answer 1

Lanthanides (Ln)
are the elements from La-Lu
(Sc and Y) sometimes included (G1 TM with similar properties and are also rare earth metals

Question 2

Why are there different versions of the periodic table?

Answer 2

There are three versions of the periodic table

a) shortened version- La and Ac in G3
b) long version -La and Ac in G3
c) long version -Lu and Lr in G3

Question 3

How were the Lanthanides discovered?

Answer 3

Late 19th century- Chemists thought they had isolated a new element from a mineral -gadolinite.
Not one new element (yttria) but instead mixture of 10 new elements
Early 20th century- Xray spectra analysed to determine there were 15 elements La to Lu

Pm was the last to be discovered
The element is radioactive and is produced artificially

Question 4

Why are Lanthanides hard to seperate

Answer 4

Properties very similar due to contracted nature of the 4f orbitals
Most display the +3 oxidation state
ionic radii very similar

Question 5

How abundant are the Lanthanides? Where are they found?

Answer 5

• Gadolinite
• Monazite LnPO4 -found globally - richer in earlier Ln
• Bastnaesite LnCO3F -found in USA and china - richer in earlier Ln

Question 6

Describe the 4f orbitals (wordier)

Answer 6

Limited radial extension- extremely contracted
Core like - penetrate the [Xe] core + held close to the nucleus

Spatially unavailable- do not extend out beyond the filled 5d and 6s orbitals and are hence screened from the ligand environment

Relatively unaffected by ligands with almost negligible crystal field effects

Cannot overlap with ligand orbitals and do not participate in bonding

Question 7

Describe the 4f orbitals numerical

Answer 7

4f orbitals have no radial nodes and 3 angular nodes
Ungerade symmetry
l=3 and hence there are 7 orbitals

Question 8

What are the two different types of f orb

Answer 8

The Cubic set- Used for higher symmetry Oh and Td

The general set- used for lower symmetry

Question 9

What does the Cubic set look like.

Answer 9

The double donut -4fn3 n=x, y, z
PICTURE
- one planar node and two conical nodes

The eight lobe
4fxyz and 4fn(n2-n2) where n= x,y,z
-three planar nodes
lobes point to the corner of a cube, face of cube on axis
45 degree rotation around each of the axis

Question 10

What does the general set look like?

Answer 10

4x flower shape- 6 lobes
1x double donut
2xeight lobe

Question 11

what is the trend in the Ln(0) and explain

Answer 11

[Xe]4fn 6s2
EXCEPTIONS
La,Ce,Gd and Lu (first two and after f7 and f14)
[Xe]4fn 5d1 6s2
Initially 5d orbitals are lower than 4f and so are filled first but as atomic number and hence Zeff increases the 4f becomes more core like, stabilised and hence lower energy and are filled first

Gd and Lu stabilise their respective electron configurations

Question 12

What is the electron configuration of Ln3+

Answer 12

La = [Xn] and from then on in plus one 4f

Question 13

Why is the chemistry of the lanthanides dominated by the +3 oxidation state

Answer 13

The fourth ionisation energy is very large (I4)
it is around 4000 kJ mol-1 compared to the third ionisation energy which is around 2000 kJ mol-1

In most cases the extra energy to remove the 4th electron cannot be compensated for by bond formation

Upon ionisation, the valence electrons are stabilised
4f, 5d, 6s but the effect occurs in order of principle quantum number

Once 3 electrons have been removed the stabilisation of the 4f orbitals is so large that the 4f are tightly held and core like and effectively inaccessable

Question 14

+2 oxidation state

Answer 14

Examination of the I3 energies reveals maxima at Eu and Yb with a high point of Sm.
Stability in the 2+ OS is due to filled/half filled and almost half filled 4f shells 
therefore Eu(II) Yb and Sm have considerable chemistry

Eu and Yb behave similarly to heavy group 2 metals
They dissolbe in liquid ammonia to form solvated electrons

Ln2+ compounds are good reducing agents



Question 15

+4 oxidation state

Answer 15

In some cases, I4 can be compensated for by bond formation
5 Ln have tetravalent chemistry:
Ce,Pr,Nd Tb and Dy
aka [Xe] and next two and [Xe}4f7 and next one
For all but Ce this is limited to solid state fluorides and some dioxides

Ce compounds show extensive tetravalent chemistry. It has higher energy 4f orbitals due to its early position in the series.

Ce4+ are good oxidising agents

Question 16

Metallic and ionic radii general trend

Answer 16

There is a gradual linear reduction of both the Ln and Ln3+ radii across the series.
This is refered to as the Lanthanide contraction.

Arises from the poor ability of the 4f electrons not being able to screen the other valence electrons from the increasing nuclear charge

aka. shielding stays same(ish) atomic charge increases, Zeff increases and hence radii decreases

VAlence electrons for Ln =6s (+5d) for Ln3+=5s and 5p
Impacts Tm: between 4d and 5d series

Question 17

Exceptions to the radii trend

Answer 17

Eu and Yb
there Metallic radii is 0.2A higher than expected (by extrapolation
This is explainable by oxidation states
for the ‘cation in a sea of electrons’ model-
Eu and Yb would be (Ln2+(e)2)
compared to other Ln whch would have Ln3+(e)3


Question 18

Which periodic table is it?

Answer 18

La and Lu-can be argued either way
La-next to Ba fits well byt Lu - nex to Hf fits well

against La
At beginning of series La electron config anomalous
-Trends many trends eg, ionic energies and and radii etc Lu fits in better w trends lanthanide contraction

Question 19

what are the rare earths?

Answer 19

ln and Sc and Y