What happens with radioactive decay in molecules?

[Nod2003]

Radon doesn’t form many compounds.  I think it will bond with fluorine but not much else that we know of.  

Radium will bond with nitrogen to make Ra3N2.  Radium decays into radon, so what happens when the radium attached to nitrogen does that?  I assume extra energy is released from breaking the bonds with the nitrogen, as radon can’t bond that way?  

[studiot]

30 minutes ago, Nod2003 said:

Radon doesn’t form many compounds.  I think it will bond with fluorine but not much else that we know of.  

Radium will bond with nitrogen to make Ra3N2.  Radium decays into radon, so what happens when the radium attached to nitrogen does that?  I assume extra energy is released from breaking the bonds with the nitrogen, as radon can’t bond that way?   

Many elements appear in several forms, known as isotopes.

Isotopes of the same element have the same number of protons and therefore the same atomic number.
But they have different numbers of neutrons, so different atomic weights.

Often some of these isotopes are radioactive and this includes isotopes of common elements like carbon (¹⁴C).

All the isotopes share most of the chemical properties of the basic (most common) version of the element.

You need to understand this before your question can be answered.

 

Edited January 27, 2019 by studiot

[Nod2003]

Sure I get isotopes, but all isotopes of both radium and radon are radioactive, so I’m not sure what point you were going for here.

[John Cuthber]

4 hours ago, Nod2003 said:

Radon doesn’t form many compounds.  I think it will bond with fluorine but not much else that we know of.  

Radium will bond with nitrogen to make Ra3N2.  Radium decays into radon, so what happens when the radium attached to nitrogen does that?  I assume extra energy is released from breaking the bonds with the nitrogen, as radon can’t bond that way?  

A couple of things happen.

Firstly the molecule is usually torn apart  by the recoil.

Secondly, the decay produces an alpha particle. It bounces round until it loses enough energy to pick up a pair of electrons and become neutral.

Those electrons are taken from something else, effectively oxidising it.

In the  middle of a piece of Ra3N2 the nitride ions would be oxidised to nitrogen atoms which would combine to make nitrogen gas.

However, the molecules are not always ripped up by the reaction.
This sort of thing was the first ever synthesis of the perbromate  ion from a radioisotope of selenium.

https://en.wikipedia.org/wiki/Perbromate

(for what it's worth, I also don't see what Studiot is on about)

Edited January 27, 2019 by John Cuthber

[swansont]

12 hours ago, Nod2003 said:

Radon doesn’t form many compounds.  I think it will bond with fluorine but not much else that we know of.  

Radium will bond with nitrogen to make Ra3N2.  Radium decays into radon, so what happens when the radium attached to nitrogen does that?  I assume extra energy is released from breaking the bonds with the nitrogen, as radon can’t bond that way?  

It takes energy to break bonds, so less energy would be released if the molecule breaks apart. But the energies involved are typically much smaller than those involved in decay (eV vs MeV)

[druS]

On 1/28/2019 at 2:53 AM, John Cuthber said:

A couple of things happen.

Firstly the molecule is usually torn apart  by the recoil.

Secondly, the decay produces an alpha particle. It bounces round until it loses enough energy to pick up a pair of electrons and become neutral.

Those electrons are taken from something else, effectively oxidising it.

In the  middle of a piece of Ra3N2 the nitride ions would be oxidised to nitrogen atoms which would combine to make nitrogen gas.

However, the molecules are not always ripped up by the reaction.
This sort of thing was the first ever synthesis of the perbromate  ion from a radioisotope of selenium.

https://en.wikipedia.org/wiki/Perbromate

(for what it's worth, I also don't see what Studiot is on about)

Hi John. Nod thanks for the post.

If I have this right when the Radium nucleus emit an Alpha particle

²²⁶₈₈Ra -> ²²²₈₆Rn + ⁴₂He

I'm presuming the Rn atom thereby has two spare electrons (annd that this would occur with all alpha particle emissions?). So the previous Ra₃N₂  molecule has become unstable - I don't think there is such a thing as Ra₂RnN₂  so wouldn't nitrogen return to it's elemental form, ditto Rn? It's easy to follow the numbers and suggest that the alpha particle becomes He with the spare electrons, but there are obviously many other molecules hanging around to pick them up.

[swansont]

14 hours ago, druS said:

Hi John. Nod thanks for the post.

If I have this right when the Radium nucleus emit an Alpha particle

²²⁶₈₈Ra -> ²²²₈₆Rn + ⁴₂He

I'm presuming the Rn atom thereby has two spare electrons (annd that this would occur with all alpha particle emissions?). So the previous Ra₃N₂  molecule has become unstable - I don't think there is such a thing as Ra₂RnN₂  so wouldn't nitrogen return to it's elemental form, ditto Rn? It's easy to follow the numbers and suggest that the alpha particle becomes He with the spare electrons, but there are obviously many other molecules hanging around to pick them up.

Nuclear decay descriptions typically ignore the electrons. Some are often left behind after the reaction — the alpha and the daughter can be left in an ionized state, as the energy released in the decay is usually much larger than the ionization energy, but that has no bearing on the decay.

Similarly, any molecule will likely be torn apart by such a decay. You need to look at the KE of the Rn when the Ra emits the alpha. The ratio of their KEs is the inverse of their mass ratio, so the Rn gets about 1.8% of the KE. Around 85 keV. How does that compare to molecular binding energies?

 

[druS]

10 hours ago, swansont said:

Nuclear decay descriptions typically ignore the electrons. Some are often left behind after the reaction — the alpha and the daughter can be left in an ionized state, as the energy released in the decay is usually much larger than the ionization energy, but that has no bearing on the decay.

Similarly, any molecule will likely be torn apart by such a decay. You need to look at the KE of the Rn when the Ra emits the alpha. The ratio of their KEs is the inverse of their mass ratio, so the Rn gets about 1.8% of the KE. Around 85 keV. How does that compare to molecular binding energies?

 

Thanks swansont, we hit my (knowledge) limit again - though if my quick google skills suffice it shows a factor in the order of 10^-3 smaller for the molecular bind. The chemical properties clearly not really involved.

[swansont]

12 hours ago, druS said:

Thanks swansont, we hit my (knowledge) limit again - though if my quick google skills suffice it shows a factor in the order of 10^-3 smaller for the molecular bind. The chemical properties clearly not really involved.

Bingo.

When I was doing my postdoc, we were detecting the Ar daughter of a beta-plus-decay of K. We had an electric field in place, which accelerated all the charged particles. The Ar was ionized in a lot of the reactions, and we detected three different ionization states (all had a different time-of-flight, owing to the acceleration) plus the beta, as well as the "shake-off" electrons, which were detected in the opposite direction. And beta decays have a far smaller recoil than alpha decays.

[John Cuthber]

In a crystalline solid like Ra3N2 it's also probable that you will end up with crystal defects.

https://en.wikipedia.org/wiki/Crystallographic_defect

and also the electrons, kicked out of the way by the reaction may fall back into place and emit light.

Some luminous paints worked on that basis.

You can also get electrons "stuck" in a crystal

https://en.wikipedia.org/wiki/F-center

[Sensei]

Wristwatches with luminous arrows are using radioactive Tritium.

https://en.wikipedia.org/wiki/Tritium_radioluminescence