Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

aa The f-elements > Meet the Lanthanides 2 > Flashcards

Meet the Lanthanides 2 Flashcards

1
Q

What are the magnetic properties of any ions the combination of contributions from

A
  1. Spin and orbital angular momenta
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What happens to orbital angular momentum in first row transition metals

A
  1. Orbital angular momentum often removed or partially quenched by interaction of the ligands with the partially occupied d orbitals
  2. Often (not always) correspond to spin only formula
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the spin only formula

A
  1. Ueff= root(n(n+2))
  2. n=number of unpaired electrons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the electronic structure of lanthanide ions governed by

A
  1. Very large spin-orbit coupling characteristic of high Z
    - means you can’t treat spin and momentum separately
  2. Very small crystal-field splitting (contracted f orbitals)
    - no partial quenching from ligands
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the Russell-Saunders coupling scheme

A
  1. Because 4f orbitals have limited radial extension and are core like
  2. They have little role in bonding- the orbital angular momentum is not quenched
  3. Magnetic properties of the Ln3+ ions are very well described from the coupling of spin and orbital angular momenta
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the Russell-Saunders coupling scheme assume

A
  1. Spins of the electron couple - total spin angular momentum (S)
  2. Orbital momenta also couple- total orbital angular momentum (L)
  3. Totall angular momentum, J, of the system is given by coupling of S and L
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the typical Ln3+ spin orbit coupling in comparison to ligand field effects and what is the result of that

A
  1. Typically large (1000cm^-1)
  2. In comparison to ligand field effects (100cm^-1)
  3. As a result only the ground J-state is populated
  4. magnetism is essentially independent of environment.
  5. Thus we only need to know the ground state of an Ln3+ ion to predict and understand its magnetic and spectroscopic behaviour.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How are atomic or ionic energy levels defined

A
  1. By a term symbol (2S + 1)LJ
  2. Ground state term symbol contains all the information needed to calculate U for a Ln3+ complex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the magnetism of Ln3+ ions

A
  1. arises from presence of unpaired 4f electrons
  2. Magnetic moments of Ln3+ complexes are little affected by the ligand environment- so similar to those calculated for the free ions
  3. Inherently very high magnetic moments
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the Russell-Saunders approach to magnetism

A
  1. Spin-orbit coupling splits the atomic or ionic term into a series of J levels
  2. Spin-orbit coupling is so large that the excited levels are inaccessible and the magnetic moment is determined by the ground state of the ion
  3. The magnetic moment of a J-state is expressed by the Lande Formula
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the Lande Formula

A
  1. Uj= g root(J(J+1)) where:
  2. g=3/2 + S(S+1)-L(L+1)/2J(J+1)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why is there no observed magnetic moment for Pm

A
  1. It too radioactive
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Do the calculated magnetic moment show a good agreement with experimental

A
  1. Yes
  2. Except Sm3+ and Eu3+
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why do Sm3+ and Eu3+ magnetic moment values not show good agreement with experimental

A
  1. Both ions have excited states close in energy to the ground term to be thermally accessible and contribute to the observed magnetic moment
  2. Low lying energetic states- different magnetic moments contributing to magnetic moment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does Sm3+ and Eu3+ magnetic moments mean for dependence on other factors

A
  1. Low lying energetic states leads to temperature dependence
  2. The observed moments at RT decreases as the temperature is lowered
  3. Thermally populated as governed by the Boltzmann distribution
  4. Excited states are closer than KT (around 200cm^-1 which is RT)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is Eu expected to not have magnetic moment

A
  1. Ground state term- 7F0
  2. 0 in J state
  3. Orbital and spin angular momentum should cancel out
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the 3 most common ores that the lanthanides are found in

A
  1. Monazite E.G lanthanide orthophosphates (LnPO4)
  2. Xenotime E.G lanthanide orthophosphates (LnPO4)
  3. Bastnaesite e.g. fluorocarbonate (LnCO3F)
18
Q

Which of the natural ores use alkali digestion and which use acid dissolution

A
  1. Monazite/ xenotime- alkali digestion
  2. Bastnaesite- acid digestion
19
Q

Describe the process of extraction from monazite/ xenotime

A
  1. Mineral dressing- crushing, grinding and hot filtration
  2. Digestion- 140 degrees/ 65% NaOH, Extract PO43- with H2O
  3. Produces slurry of impure hydrous oxides of Ln
  4. Add HCl with pH 3
  5. Produces impure solution of LnCl3
20
Q

Describe the process of extraction from bastnaesite

A
  1. Mineral dressing
  2. Produces CO2
  3. Add H2SO4, 200 degrees
  4. Leach H2O
  5. Produce solution of Ln2(SO4)3
21
Q

What are the problems with extraction from native ores using alkali/acidic methods

A
  1. Enormous amount of waste
22
Q

What is history of separation and isolation of Lanthanide

A
  1. Until 1950 most separations involved hundreds of tedious fractional crystallisations of compounds
23
Q

Which two Lns were easier to extract

A
  1. Cerium and Europium
  2. Exploit availability of 4+ and 2+ OS respectively
24
Q

Give an example of extraction of Ce

A
  1. Oxidise only Ce to M4+ using HClO or KMnO4, KIO3
  2. Ce3+ –> Ce4+–> Ce(IO3)4 precipitates
25
Q

Give an example of extraction of Eu

A
  1. On action of Zn/Hg, only Eu forms a stable M2+ that does not reduce H2O
  2. Then isolate by precipitation as EuSO4
  3. Eu3+ –> Eu2+ –> EuSO4 precipitates
26
Q

What are ion exchange methods

A
  1. Spin off from the Manhattan Project- makes use of the lanthanide contraction
  2. The mixed lanthanides are loaded on to a cation-exchange resin and then eluted with a suitable complexing agent like EDTA or citric acid
27
Q

How does the ion exchange method separate the Lns

A
  1. Heavier, smaller lanthanides are better Lewis acids so form stronger EDTA complexes
  2. Removed from the resin first in the order of their stability constants e.g. decreasing atomic number
28
Q

Describe the process of solvent extraction

A
  1. Favoured process since 1960s
  2. Aqueous solution of the mixed lanthanide(3+) cations extracted into a non-polar organic liquid (kerosene)- contains around 10% of DEHPA or TBP
  3. As in chromatographic process, smallest/heaviest lanthanides form the most stable TBPO complexes and are extracted most efficiently in a series of continuous counter-current extractions
29
Q

What methods are used to extract Ln

A
  1. Extraction from natural ores
  2. Ion exchange
  3. Solvent extraction
30
Q

What is a new way that could be used to extract Ln

A

1.Using magnetic moments information and big magnetic field

31
Q

How can you produce elemental metals

A
  1. Individual lanthanides prepared by metallothermic reduction of the anhydrous lanthanide fluorides or chlorides with calcium meal
  2. LnX3 –> Ln
32
Q

What are the conditions for the metallothermic reduction to produce Ln elements

A
  1. Performed under argon and the product is a Ca/Ln alloy from which the Ca is removed by distillation as has lower BP
  2. 300 degrees
33
Q

When can metallothermic reduction not be used to produce elemental metal

A
  1. Metals with tendency to form a divalent state (Sm, Eu, Yb)
  2. Only reduce to the 2+ state
34
Q

How do you produce elemental metals when metallothermic reduction cannot be used

A
  1. By reduction of their oxides with lanthanum
  2. 2La + M2O3 –> La2O3 + 2M
  3. M= Sm, Eu, Yb
  4. The divalent lanthanides are more volatile and can be removed by distillation
35
Q

Describe the properties of the Ln metals

A
  1. Rather soft
  2. Silvery white
  3. Later Ln are harder
  4. Tarnish in air due to their highly electropositive character
36
Q

Describe the reactivity of the Ln metals

A
  1. Simple Ln compounds are strongly ionic
  2. Burn easily in air to form sesquioxides, M2O3
  3. React with N2 slowly to form ionic nitrides LnN
  4. Undergo exothermic reaction with H2 to yield ionic hydrides MHn (n=2,3)
37
Q

What is produced when Ln + H2O

A
  1. M2O3 or M(OH)3 + H2 - slow if cold, rapid if heated
38
Q

What is produced if Ln + H+ (Dilute acid)

A
  1. Ln3+ + H2 - rapid at RT
39
Q

What are uses of metals

A
  1. Mischmetall - 50%Ce, 25%La, 25% other light Lns
  2. Pyrophoric- allowed with 30% Fe it is used in lighter flints
  3. <1% Mischmetall or Ln silicides improves the strength and workability of low alloy steels for plate and pipes
40
Q

Comment on values of magnetic moment and why Sm is different

A
  1. The values should be correct due to the magnitude of spin-orbit coupling as Sm is a heavy atom and the limited interaction of the 4f valence orbitals with the ligand field hence no quenching
  2. means there is no quenching of L (orbital angular momentum)
  3. but Sm shows deviation from expected moment
    due to low lying excited J states
41
Q

Describe why all simple salts of Ln have the same colours

A
  1. The colours in trivalent lanthanides originate from f-f transitions.
  2. These originate from disparate energies of the S, L and J-states i.e. repositioning the electrons in different orbitals, pairing of electrons, or changes in spin orbit coupling, not crystal field
  3. and are thus not dependent on environment
  4. Dependent on identity of the element as the 4f orbitals are core-like and do not interact with the ligands

aa The f-elements (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions