2: Intro to Actinides Flashcards
What is the Manhattan project?
WWII project development of Nuclear weapons as well as nuclear power, nuclear medicines and lanthanide based technologies
What are actinides?
Actinides (An) 15 elementsfrom Ac to Lr with either in G3 5f series- second row of the f block First 7 element-compounds similar to early transition states Last 8 element-compounds similar to those of 3+ ion Lanthinide complexes All isotopes of all the actinides are radioactive
What is the brief history of An
Initially proposed in 1944 Th, Pa and U as G 4,5,6
What is trans-Uranium
Z>92, elements beyond uranium, trans-uranium elements are synthetic and are typically formed by neutron capture/heavy ion bombardment Picture!!
Do Actinides naturally occur?
First 4 Ac-U all occur naturally Ac and Pa in trace, U and Th are relatively abundant
Thorium general
-Widely dispersed -3ppm of earth’s crust -Naturally occurs as 100% 232-Th -Occurs in monazite and uranothorite -Obtained as ThO2 from mineral extraction processes
Uranium general
- widely distributed
- found in the faults of old igneous rocks
- Naturally 99.28% 238 and 0.71% 235
What are 5f orbitals
-4f and 5f do not differ in the angular part of their WF and are same shape, 5f orbitals have a radial node!!!! 5f have a greater radial extention w/r to 6s/p orbitals THAN the 4f have w/r to 5 s/p orbitals . (rel effect) -5f orbitals are less shielded from influence of ligands (aka more expopsed) resulting in a larger contribution to covalent bonding earlier in the An series eg UF3-covalent contribution -NdF3 - not
What are “relativistic effects” and why to do with An?
- it is believed that relativistic effects partially determine the chemistry of An’s -Increasing v of e’s orbiting heavy nuclei results in a relativistic contribution to mass 1s in U –> 1.35 me (as v approaches c, m approaches infinity) DROC, direct rel orbital contraction: All s-orbital (and to a lesser extent p-orbitals0 are stabilised IROE, indirect rel orbital expansion: All d and f orbitals are now destabilised- due to the increased shielding of nuclear charge by the now contracted s and p orbitals -the result is an increased radial extension of the 5f orbitals w/r to 6s/6p
What is the electronic configuration of the An’s
-not as easy to confirm Ac - Np: 6d orbitals are lower in energy = 6d filling favourable [Rn]5fn 6d1 7s2 Pu+ 5f stabilized to such an extent =6d filling no longer favourable [Rn]5fn 7s2 Exceptions: Cm/Lr due to half-filled shell and filled shell increasing Zeff stabilises 5f -takes on first five structure 5f orb is more contracted and interacts less with ligand fields -> more lanthanide like
Ionic radii and metallic radii
Ionic radii show a clear actinide contraction for 3+,4+ and partial 5+ ions actinide 3+ and 4+ ions with similar radii to their lanthanide counterparts show similarities in properties that depend on ionic radii Metallic radii show no discernable trend, however the increased radii may reflect the stability of the 3+ OS while early actinides can access high oxidation states???? Picture
Where would you find an Actinide in your home?
Smoke detectors Radiation source w a radiation detector smoke particles get between - disrupt radiation que alarm
The binary halids of actinides
Group valency can be achieved up to U, eg. UF6, PaF5 ThF4 After Uranium the 3+ oxidation state becomes more stable and the halides are mostly MX3 and resemble the lanth trihalides
why is UF6 a very useful act. halide
It is made on a large scale to seperate 235UF6 and 238UF6 and producing 235UF6 enriched 235
Why is enriched uranium important
235-fissile-slower moving neutrons can cause fission –> chain reactions 238-fissionable-fast energetic neutrons only Nuclear fission occurs when a large nucleus is bombarded with a neutron and splits into 2 smaller nuclei, releasing one or more neutrons which can collide with other nuclei For chain reactions, a critical mass of fissile material is required Uranium 235- fissile uranium enriched w 235 from 0.71% to 3-5%
How is UF6 prepared?
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