March 28, 2024, 07:57:44 AM
Forum Rules: Read This Before Posting


Topic: Why U(VI) exists as Uranyl  (Read 14939 times)

0 Members and 1 Guest are viewing this topic.

Offline pranay29

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +1/-0
Why U(VI) exists as Uranyl
« on: January 10, 2012, 09:00:14 AM »
Why U(VI) exists as uranyl ion i.e. UO2+2, not as U+6?

Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re: Why U(VI) exists as Uranyl
« Reply #1 on: January 10, 2012, 12:37:33 PM »
I'm going to give a watered down answer. Not many metals (I can't think of one) can exist as a pure +6. Think about it, it would be so positive that it would tend to scrape electrons from anything near it due to Coulomb attraction.
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex

Offline gippgig

  • Full Member
  • ****
  • Posts: 139
  • Mole Snacks: +8/-2
Re: Why U(VI) exists as Uranyl
« Reply #2 on: January 10, 2012, 09:34:21 PM »
So why does heptavalent Np & Pu exist as the XO53- complex?

Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re: Why U(VI) exists as Uranyl
« Reply #3 on: January 11, 2012, 12:12:58 AM »
So why does heptavalent Np & Pu exist as the XO53- complex?

Unfortunately, I neither have a watered down answer nor an advance answer to address that question.
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex

Offline vmelkon

  • Chemist
  • Full Member
  • *
  • Posts: 474
  • Mole Snacks: +28/-10
  • Gender: Male
Re: Why U(VI) exists as Uranyl
« Reply #4 on: January 11, 2012, 01:34:25 PM »
I thought that U6+ existed, for example UF6 (Uranium Hexafluoride)
http://en.wikipedia.org/wiki/File:Uranium_hexafluoride_crystals_sealed_in_an_ampoule.jpg


Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Why U(VI) exists as Uranyl
« Reply #5 on: January 11, 2012, 02:02:59 PM »
I thought that U6+ existed, for example UF6 (Uranium Hexafluoride)

Not in a water solution. I have a gut feeling UF6 is more covalent than ionic.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re: Why U(VI) exists as Uranyl
« Reply #6 on: January 11, 2012, 02:12:39 PM »
I thought that U6+ existed, for example UF6 (Uranium Hexafluoride)

Good point, I stand corrected. However, since the subllimation point is so low (56.5 °C) it would be better to consider it a covalent molecule and not as an ionic one. How many traditional ionic salts can melt at such a low temperature?

Although, the oxidation state for uranium is (VI), I think we have to be very careful in extrapolating this to uranium behaving as a cation (U6+).
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex

Offline snorkack

  • Regular Member
  • ***
  • Posts: 51
  • Mole Snacks: +5/-1
Re: Why U(VI) exists as Uranyl
« Reply #7 on: February 13, 2014, 05:07:37 PM »
So why does heptavalent Np & Pu exist as the XO53- complex?
Probably something related to ligand field preferred geometry. Heptavalent elements occur as XO4- (X=Cl, Br, I, Mn, Tc, Re), XO65- (X=I), I think I also forms some IO53- complexes.  Not sure why Np and Pu prefer their specific geometry.

Sponsored Links