f-block and nuclear chemistry Flashcards
What ore was uranium discovered in and when (roughly)?
Pitchblend, 1789 (Late 18th century)
Name 4 ways that some of the f-block elements were discovered
Neutron bombardment
2H (deuterium) bombardment
Alpha-particle bombardment
Thermonuclear detonation
Describe the general abundance of the f-block elements, with some key examples
Called the rare earth metals, but aren’t that rare.
La/Ce/Nd more common than Pb.
Nd (used in lasers) is more abundant than Au.
Tm is the least abundant but there’s more in the earth’s crust than iodine.
What are the names of the 4f and 5f elements
4f= lanthanides 5f= actinides
Why is Promeithium (Pm) absent from the earth’s crust?
All isotopes of Pm have short half-lives.
Describe and explain the pattern of the lanthanides abundance in the earth’s crust
Even-odd alternation of abundance with atomic number. Even nuclei are more stable hence the nuclear stability follows this pattern.
How is Pa found?
Found only as a decay product in Uranium (U) supplies.
What is a key difference between the oxidation properties of the lanthanides/actinides?
None of the lanthanides change oxidation state, whereas can change the oxidation states of the actinides.
How do you separate a solution containing a mixture of lanthanides (all in a single oxidation state)?
Use an ion exchange column (eg colloidal Prussian blue).
What is the structure of ‘hex’?
UF6
Describe the structure of f-orbitals compared to d-orbitals
f-orbitals are like d-orbitals but have more angular nodes (more lumpy).
f-orbitals are well shielded by other electrons, but they stabilise very quickly upon oxidation (especially impo with 4f orbitals).
How does the size of the lanthanides change as you progress from the left—> right of the periodic table? Explain why this happens
The size of the ions decreases- lanthanide contraction. Similar to other trends in periodic table (increasing Zeff), was thought that this was solely due to increasing Zeff, but it has been shown that 30% of the contraction was due to the RELATIVISTIC EFFECT.
What is Zeff?
Effective nuclear charge
What is the relativistic effect and how does it contribute towards the lanthanide contraction?
As the electron in the orbital approaches the nucleus, its speed increases significantly, approaching the speed of light (~70% c). Because of the relativity, the mass of the electron gets bigger (by about 35%). This effect is especially true for highly charged nuclei. 4f electrons spend their time nearer to the nucleus hence are CORE LIKE.
How many f-orbitals are there?
7
What are the 2 sets of f-orbitals and why is there more than 1 set?
General and cubic set. Due to different solutions to the Schrodinger wave equation for f-orbitals.
What is the symmetry of the f-orbitals?
Ungerade
Describe and explain the ligand interaction with (4) f-orbitals
Weak ligand interaction (similar to 3d orbitals) due to high angular nodality and the ‘core-like’ nature of the 4f orbitals.
How many nodes are there in the radial distribution function of the 4f and 5f orbitals?
4f= none 5f= 1
What do nodes prevent?
Penetration towards the nucleus.
Why is there little difference in the ionic radii of the 4d and 5d transition elements?
Lanthanide contraction (due to increasing Zeff and relativistic effects).
Describe the effects of the relativistic effect on radial distribution functions
Orbitals have a radius which is dependent of 1/mass of the electron in that orbital; the relativistic effect decreases the radius of the orbital. Due to screening caused by the relativistic contraction of the s-orbitals, the f-orbitals undergo an INDIRECT relativistic expansion.
What orbital is particularly affected by the relativistic contraction?
s-orbital
Compare the indirect relativistic expansion between lanthanides an actinides and the consequences of this.
Lanthanides= small
Actinides= significant, meaning that the s f orbitals can overlap with the ligands.
Therefore lanthanides and actinides display very different chemical properties.
Compare the bonding between lanthanides and ligands with actinides and ligands
Lanthanides and ligands= covalent
Actinides and ligands= ionic
According to what principle do the f-block orbitals fill and where are the anomalies?
The Aufbau principle; anomalies at half-filled (f7) and filled f-orbitals (f14).
Explain the significance of the half-filled and filled f-orbitals and how this affects ionisation
They have unusual stability hence ionisation will nearly always result in half-filled/filled f-orbitals (ionisation may occur out of the 5/6d orbitals).
Explain how the 4f orbitals change upon ionisation and how this prevents further ionisation past the +3 ox state
Because there are no nodes in the 4f orbitals, they are sensitive to the nuclear charge and drop quickly in energy upon ionisation. As we reach the +3 ox state, they are so low that we can’t easily ionise further.
What is the general trend in lanthanide metallic radii and the exceptions?
Across the row there is a decrease in the metallic radii due to an increase in Zeff and the ion getting smaller. Exceptions= Eu and Yb due to the unusual effects of a half-filled/filled f-level.