The effect of additional neutrons

[druS]

I'm trying to fathom what is happening when an atom has additional (or fewer!) neutrons than the number of protons - different atomic isotopes. Generally I understand that chemical properties are set by the quantity of protons/electrons and the relationship or "closeness" that the electron orbit has to the valence electrons. (Happy to have my clumsy language corrected).

Why does/can a nucleus adopt additional or fewer protons - at all? Then it seems to make a little sense that the more massive nucleus might have "space" for additional protons - why does it happen with hydrogen?

What are the differences in chemical properties for different isotopes and why? I understand as an overview, there are no practically discernable differences in chemical properties, albeit there is radioactivity in the larger isotopes. In detail however, that isn't the answer is it? In Hydrogen, between ¹H, ²H and ³H there is an incredible proportional difference in atomic mass of 200% or 300%. I have read that reaction times can be different. Anything else?

 

 

 

[pavelcherepan]

1 hour ago, druS said:

Generally I understand that chemical properties are set by the quantity of protons/electrons and the relationship or "closeness" that the electron orbit has to the valence electrons. (Happy to have my clumsy language corrected).

Well, chemical properties of an atom are all related to the valence electrons and in turn the configuration of an electron shell depends on the number of protons in the nucleus. Note, number of neutrons in the nucleus doesn't affect chemical properties much which can be seen from different isotopes of atoms participating in the same chemical reactions with the same results.

1 hour ago, druS said:

Why does/can a nucleus adopt additional or fewer protons - at all? Then it seems to make a little sense that the more massive nucleus might have "space" for additional protons - why does it happen with hydrogen?

I'm not an expert on this matter, but in modern understanding nucleus is not just some different colored balls attached to one another as it's often portrayed. Instead, the nucleus is a 'soup' of mostly two flavours of lighter quarks (up and down) with gluons zipping around between those. Quarks regularly change flavours and it's all very complex. 

Now to your question - usually a nucleus can have more of fewer protons than needed is either by simply being created that way, possibly as a decay product of another radioactive nucleus; it can absorb neutrons coming off of another nucleus which is how nuclear fission works or it can even be created by clamping together couple lighter nuclei as in case of fusion.

1 hour ago, druS said:

What are the differences in chemical properties for different isotopes and why? I understand as an overview, there are no practically discernable differences in chemical properties, albeit there is radioactivity in the larger isotopes. In detail however, that isn't the answer is it? In Hydrogen, between ¹H, ²H and ³H there is an incredible proportional difference in atomic mass of 200% or 300%. I have read that reaction times can be different. Anything else?

As I said before, there's little differences in terms of chemical properties between isotopes as they all have exactly the same electron configuration. 

Edited February 9, 2018 by pavelcherepan

[Sensei]

3 hours ago, druS said:

Why does/can a nucleus adopt additional or fewer protons - neutrons at all? Then it seems to make a little sense that the more massive nucleus might have "space" for additional protons - neutrons why does it happen with hydrogen?

You meant "additional or fewer neutrons", rather than protons. Hydrogen with additional proton, would not be Hydrogen anymore, but Helium.

Nucleus is ultra small in comparison to entire atom.

If you have atom, and you will bombard it by free neutrons, they can join together. It's called neutron capture.

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

During explosion of nova/supernova star there are also happening rapid neutron capture (r-process)

https://en.wikipedia.org/wiki/R-process

and slow neutron capture (s-process)

https://en.wikipedia.org/wiki/S-process

 

3 hours ago, druS said:

What are the differences in chemical properties for different isotopes and why? I understand as an overview, there are no practically discernable differences in chemical properties, albeit there is radioactivity in the larger isotopes. In detail however, that isn't the answer is it? In Hydrogen, between ¹H, ²H and ³H there is an incredible proportional difference in atomic mass of 200% or 300%. I have read that reaction times can be different. Anything else?

Hydrogen/Deuterium/Tritium have tiny different ionization energy and spectral lines. Thus their discharge tubes have slightly different colors.

Tiny difference at quantum level, means dramatic consequences at macroscopic level. Drinking heavy water kills mammals (rats) after week.

 

Edited February 9, 2018 by Sensei

[swansont]

9 hours ago, druS said:

I'm trying to fathom what is happening when an atom has additional (or fewer!) neutrons than the number of protons - different atomic isotopes.  

There are just two instances of stable isotopes with fewer neutrons than protons, and they are very, very light nuclei (H-1, He-3). The neutrons and protons attract each other, but protons repel. So H-1, which only has the one proton, is fine, but the repulsion of two protons requires a neutron for He-3 to be bound, and for more protons, you need the additional neutrons.

 

[BabcockHall]

The various isotopes produce can produce a kinetic isotope effect that is useful in understanding the mechanisms of reactions, including enzyme-catalyzed reactions.  The various isotopes have different spectroscopic properties that are especially evident in nuclear magnetic resonance spectroscopy.

[druS]

Thanks guys - apologies at not responding earlier - we've had some family health matters that changed my focus for a bit.

Int ereseted in the comment that a nucleus being a soup of quarks - sounding like an modern update on the plum pudding model of the atom. (Ok, not really but interesting anyway.)

Are their any thoughts on "why"? Why does carbon do C12 and C14, for instance?

[Sensei]

1 hour ago, druS said:

Are their any thoughts on "why"? Why does carbon do C12 and C14, for instance?

Radioactive Carbon C-14 can be made after bombarding stable Nitrogen N-14 in air by free neutron in reaction, e.g.:

[math]_7^{14}N + n^0 \rightarrow _6^{14}C + p^+[/math]

Free neutron is made in reaction caused by cosmic-ray particles (mostly relativistic accelerated particles from the Sun) e.g.

[math]p^+ + p^+ \rightarrow p^+ + \pi^+ + n^0[/math]

Free neutron has to have enough kinetic energy to cause this reaction. Slow thermal neutron will not knock free proton away.

 

[swansont]

12 hours ago, druS said:

Thanks guys - apologies at not responding earlier - we've had some family health matters that changed my focus for a bit.

Int ereseted in the comment that a nucleus being a soup of quarks - sounding like an modern update on the plum pudding model of the atom. (Ok, not really but interesting anyway.)

Are their any thoughts on "why"? Why does carbon do C12 and C14, for instance?

C-14 is unstable, so while nature "does" C-14, it also tries to un-do it.

Stability with regard to beta decay is a matter of whether a neutron or proton can get to a lower energy by converting from one to the other. Nuclear structure is such that paired particles tend to have a lower energy, so even number of neutrons are more likely to be stable, especially in larger nuclei.

In carbon, we have C-12 and C-13 being stable. We have an even number of protons, so that tends to be a nice, stable state, and C-12 has even numbers of both, which is consistent with its larger relative abundance. The extra neutron in C-14 can get to a lower energy state by converting to a proton. The result, N-14, is the heaviest stable nucleus with both an odd number of neutrons and protons. Heavier nuclei tend to have more neutrons, and the even numbers, as the nuclear energy states become more complex.

[druS]

11 hours ago, Sensei said:

Radioactive Carbon C-14 can be made after bombarding stable Nitrogen N-14 in air by free neutron in reaction, e.g.:

147N+n0→146C+p+

Free neutron is made in reaction caused by cosmic-ray particles (mostly relativistic accelerated particles from the Sun) e.g.

p++p+→p++π++n0

Free neutron has to have enough kinetic energy to cause this reaction. Slow thermal neutron will not knock free proton away.

 

 

Now that is interesting though have to say beyond my current knowledge ability. So we create a new nucleus by forceably removing a neutron proton [self edit]. Presumable the "un-required" electron simply matches?

Edited March 2, 2018 by druS

[swansont]

1 hour ago, druS said:

 

Now that is interesting though have to say beyond my current knowledge ability. So we create a new nucleus by forceably removing a neutron proton [self edit]. Presumable the "un-required" electron simply matches?

It's quite likely that at least one electron would be dislodged by the collision. In any event, the equilibration of the charge involves a much smaller energy than the nuclear reaction.

[Sensei]

On 2.03.2018 at 1:01 PM, druS said:

Now that is interesting though have to say beyond my current knowledge ability. So we create a new nucleus by forceably removing a neutron proton [self edit].

Each atom, each isotope, even if it's otherwise perfectly stable, has different energy required to destroy nucleus. There can be human induced destruction of nucleus by adding this "missing energy".

It's called induced radioactivity/artificial radioactivity.

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

 

On 2.03.2018 at 1:01 PM, druS said:

Presumable the "un-required" electron simply matches?

Electron after event will be ejected, no longer electrostatically attracted by nucleus.

 

Edited March 3, 2018 by Sensei

[OldChemE]

and in addition to much already said, neutrons help to stabilize the nucleus by spreading out the repulsive effect of the charge on the protons.  As you add neutrons, stability improves to a point, but with too many neutrons the dynamics of the nucleus (the parts don't stand still) reach a point where stability declines again.  This is why you see a limited range of viable isotopes for elements.