Why does neutral fluorine so reactive?

[idea2000]

Hi,

I'm a novice at quantum and I was just wondering why an electrically neutral fluorine atom needs to absorb an electron to make itself electrically unbalanced with a new -1 charge? In our general chemistry class, the explanation was that the fluorine atom for some unexplained reason wants to complete it's valence octet even if it means ending up with more electrons than protons. I was wondering if quantum mechanics offers a deeper explanation other than just needing to complete its octet?

 

[Borek]

Quantum mechanics explains what the octet is and allows calculation of its energy. You will not get much further that that.

 

[Studiot]

why an electrically neutral fluorine atom needs to absorb an electron to make itself electrically unbalanced with a new -1 charge?

If a flourine (or any other) atom completely gains an electron it is no longer an atom it is an ion.

Now flourine takes part in many electron sharing (covalent) bonding situations where overall electrical neutrality is preserved. The charge shift in this type of bonding is less.

When flourine does become an ion it either happens in solution where there are balancing charges nearby or it the ion has a very short life. You can't get a bottle of flourine ions under normal circumstances.

 

[Borek]

When flourine does become an ion it either happens in solution where there are balancing charges nearby or it the ion has a very short life. You can't get a bottle of flourine ions under normal circumstances.

What about bottle of solid NaF? No solution, plenty of stable fluorine ions. And even not that expensive, I can get it for about $30 per kg (end user price for small quantity).

 

[Studiot]

And there are no electrically balancing positive sodium ions in the bottle?

If you want to offer me a bottle of flourine ions , like I posted, that would be a different matter.

 

[Borek]

If you want to offer me a bottle of flourine ions , like I posted

You have not stated they have to be isolated and there should be no counterions present :tongue2:

And your statement

When flourine does become an ion it either happens in solution where there are balancing charges nearby or it the ion has a very short life.

is - as shown by solid ionic flurodies - incomplete.

 

[alxm]

There are several reasons for why full orbitals are more stable. The biggest one is that it minimizes the http://en.wikipedia.org/wiki/Exchange_interaction" and leads to spherical symmetry.

It's counter-intuitive that an atom would 'voluntarily' go to a non-neutral charge, but it's important in this context to realize that the electrons are in motion,
and compensate by correlating that motion (i.e. "avoiding" each other), so the electrons don't experience the full charge the same way as if they'd been stationary.

 

[Studiot]

is - as shown by solid ionic flurodies - incomplete.

Yes of course it's incomplete. Idea has just stated that he or she is just starting quantum mechanics and asked the same question we asked when I was starting QM 45+ years ago.

I think it to be a worthwhile question which shows the student is thinking about different things that are said to him and trying to reconcile them.

Why could you not offer some words of helpful encouragement/explanation, rather than quibbling with my offering that did not directly bear on what you said?
ALXM managed to do just this.

My point was that it is unusual to find free isolated ions of flourine. They can be stable when they exist as part of an electrically balance whole.

Although I did not specifically mention them, solid ionic compounds are included in that description.

 

[SpectraCat]

There are several reasons for why full orbitals are more stable. The biggest one is that it minimizes the http://en.wikipedia.org/wiki/Exchange_interaction" and leads to spherical symmetry.

It's counter-intuitive that an atom would 'voluntarily' go to a non-neutral charge, but it's important in this context to realize that the electrons are in motion,
and compensate by correlating that motion (i.e. "avoiding" each other), so the electrons don't experience the full charge the same way as if they'd been stationary.

Well, it may be counter-intuitive, but that fact is that *most* atoms, not just fluorine, have positive gas-phase (i.e. in vacuo) electron affinities, meaning that acquiring an additional electron is actually an exothermic process across most of the periodic table, with the most notable exception being the noble gases.

I agree with your phenomenological explanation, however I would add the following. From the point of view of a free-electron, the nuclear charge of an atom with an incomplete electronic shell is not completely screened by the electron cloud. Thus the free-electron "feels" an attractive coulomb interaction with the formally neutral atom, and is able to lower the total energy of the system by forming an anion.