When Cl, Br, I turn into Cl+, Br+ and I+?

[HCverma]

Main Question or Discussion Point

As we know that Cl, Br and I are highly electronegative elements, the receive electrons and become Cl-, Br- and I-. But my question is in which situation, they start donating electrons and become Cl+, Br+, and I+?

 

[Charles Link]

This is sort of a guess on my part, because I have never seen an arc lamp with these elements,(=I don't think there's any reason why it couldn't be done=it would just require higher voltages). If you were to make an arc lamp (arc discharge lamp=e.g. the same kind of arc that is used in fluorescent lamps) with the gas of any of these diatomic molecules, it would necessarily create positive ions. $\\$ Additional item: I do believe it is likely the atomic spectrum has been studied in detail for these elements and ions in such a discharge. $\\$ See also: http://rspa.royalsocietypublishing.org/content/136/830/585

 

[TeethWhitener]

But my question is in which situation, they start donating electrons and become Cl+, Br+, and I+?

What is the chemical term for losing electrons?

 

[Lord Jestocost]

Cl⁺ ions are, e.g., formed in Cl₂–Ar based plasmas which are used for plasma etching in semiconductor treatment.

 

[HCverma]

What is the chemical term for losing electrons?

Cations

 

[TeethWhitener]

Cations

No, cations are positively charged species. But Cl^- can lose an electron to become neutral chlorine, for example:

$$\textrm{2Cl}^- \longrightarrow \textrm{Cl}_2 + \textrm{2e}^-$$

What is the term for the process above, when a chemical undergoes a reaction which specifically causes a loss of electrons?

 

[snorkack]

Cl(I), Br(I) and I(I) are mildly acidic species. In aqueous environment, they are likely to occur as HClO, HBrO and HIO, which have a weakly acidic character and in strong base form ClO^-, BrO^- and IO^- anions.
But in acidic environment? Cl₂/AlCl₃ reacts like the reaction had been
Cl₂+AlCl₃⇔Cl⁺+AlCl₄^-. But from the behaviour of the mixture, it appears that the Cl-Cl bond does not quite break and Cl⁺ does not appear as a free cation at these conditions.
Are there any conditions where it does?

 

[HCverma]

No, cations are positively charged species. But Cl^- can lose an electron to become neutral chlorine, for example:

$$\textrm{2Cl}^- \longrightarrow \textrm{Cl}_2 + \textrm{2e}^-$$

What is the term for the process above, when a chemical undergoes a reaction which specifically causes a loss of electrons?

The term is called oxidation.
But here 2Cl^- forms Cl2 by sharing two electrons through the .covalent bond. So how do Cl^- lose electron rather than sharing a pair of electrons? Could you explain it, please?

 

[snorkack]

But here 2Cl^- forms Cl2 by sharing two electrons through the .covalent bond. So how do Cl^- lose electron rather than sharing a pair of electrons? Could you explain it, please?

Turns out that free Cl⁺ and even I⁺ cannot quite be made.
The approach would be:
React Cl with an element even more electronegative than Cl. Such as F, forming, for example, ClF.
Cl would have the positive charge. ClF is a polar covalent compound, though - the electron pair is still partially shared with Cl.
Then bond F to some ligand whose empty orbital gives a strong covalent bond to F^-, forming a weakly basic anion. Like:
ClF+BF₃→Cl⁺+BF₄^-
But Cl⁺ is too strongly polarizing cation to be dissociated in that way. Even I⁺ cannot be made - compounds with strongly electronegative groups are still covalent unless the positive charge is spread across ligands.

 

[TeethWhitener]

The term is called oxidation.

This was the point I was trying to make. You'd need to oxidize the halogen to get a halonium.

But here 2Cl^- forms Cl2 by sharing two electrons through the .covalent bond.

No, simply sharing the electrons would give you Cl₂^2-. To get rid of the electrons requires an oxidizer (something that accepts electrons).

Turns out that free Cl+ and even I+ cannot quite be made.

I'm assuming that the OP was talking about formal halonium. Free H⁺ can't be made in solution either (apart from briefly upon exposure to something like high energy radiation), but it's useful to talk about acid-base chemistry as if free protons did exist in solution.

 

[HCverma]

This was the point I was trying to make. You'd need to oxidize the halogen to get a halonium.

No, simply sharing the electrons would give you Cl₂^2-. To get rid of the electrons requires an oxidizer (something that accepts electrons).

I'm assuming that the OP was talking about formal halonium. Free H⁺ can't be made in solution either (apart from briefly upon exposure to something like high energy radiation), but it's useful to talk about acid-base chemistry as if free protons did exist in solution.

Could you name the oxidizer please and could you mention the reaction where we can get neutral Cl2?

 

[TeethWhitener]

Could you name the oxidizer please and could you mention the reaction where we can get neutral Cl2?

I'm a bit confused by your question. Do you want to know how to oxidize chloride (Cl^-) to chlorine (Cl₂)? The easiest way to do that is electrochemically (electrolyze an aqueous solution of NaCl, for example, and adjust the pH so that free Cl₂ is released). You can also oxidize HCl with potassium permanganate, for example.

 

[snorkack]

I'm assuming that the OP was talking about formal halonium. Free H⁺ can't be made in solution either (apart from briefly upon exposure to something like high energy radiation), but it's useful to talk about acid-base chemistry as if free protons did exist in solution.

If that's sufficient, then a lot of things count.
Like iodine monochloride. The liquid (freezes at 27 Celsius, boils at 97) conducts electricity, and is thereby electrolyzed to I₂ and Cl₂.
It is therefore useful to talk about iodine monochloride as dissociating:
ICl⇔I⁺+Cl^-
The actual ions in the liquid are more associated, more like
3ICl⇒I₂Cl⁺+ICl₂^-
You do not even need to use an electronegative element to take an electron from iodine. Element iodine itself can easily be molten (triple point pressure 120 mbar, melts at 114 Celsius, boils at 184 Celsius with liquid range of 70 Celsius - just because iodine vapour is so conspicuously coloured does not mean that iodine will sublimate without melting from a closed vessel). And molten iodine conducts electricity. You can simplify it as a spontaneous electrolytic dissociation with dismutation:
I₂⇔I⁺+I^-
though the actual reaction is, again, more like
3I₂⇔I₃⁺+I₃^-

 

[James Demers]

To answer the original question, you'd need extreme conditions to oxidize a Cl atom to a Cl⁺ (chloronium) ion. Powerful oxidants like elemental fluorine can pull electrons from chlorine, but there's no chemical process that can generate free Cl⁺, as it will always be bonded in some way to whatever atoms or molecules happen to be present. I suspect that you can only find isolated Cl⁺ ions in an ionized plasma, as noted above.
The same goes for bromine and iodine. There are commercially available reagents, such as bis(pyridine)iodonium tetrafluoroborate, that contain iodonium ions in a complexed state, but to my knowledge there are no simple salts containing isolated I⁺ ions.

Hypochlorite (bleach) will oxidize chloride to chlorine if you lower the pH (this is why you should never add acid to bleach.) Formally, it's
Cl⁺ + Cl^- → Cl₂
but the "positive" chlorine is actually bonded to oxygen, in the form of a hypochlorite anion, ClO^-.