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amanda.castro

Could cations and nonpolar substances react?

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Hello!

Someone, please, tell me if it is possible cations react with nonpolar molecules. Is there any rule for it or depends on both, the cation and the molecule?

I ask this because, from what i understand, for example, in reaction of Mg (OH)2 + H2O -> Mg2+ + 2OH-, Mg2+ is ionized so is unstable (actually i think he is stable because it has 8 electrons in the layer valence, but nevertheless is charged 2+).

So, let's say i have this solution another polar substance, eg, XY, where X is more electronegative than Y. So, i thought would link to Mg2+ forming MgXY because X has a negative pole.

Then I wondered: What if the substance is nonpolar?

Thank you!

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I think a cation can react with non polar species as in coordination compounds.

For example, oxo-ligand compounds where oxygen act as a ligand.

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To my limited knowledge, H+ serves every day in reactions with ethylenic compounds which are essentially nonpolar. This reaction makes much of gasoline, in refineries' alkylation units.

 

Magnesium hydroxide is very little soluble, but if we take NaOH as an alternative example, Na+ is just a simplified writing. As you noted, Na+ won't stand isolated because it attracts electrons and OH-.

 

In a polar solvent, especially water, writing Na+ and OH- only means that they can be separated by water molecules. If the water molecules are properly oriented and make a chain between both ions, there is nearly no bare charge in the solution.

 

A little bit more subtle: each ion has several neighbour water molecules, and these molecules aren't as strongly polarized to have one electron less at one side and one more at the other. Both effects can about compensate. In addition, every Na+ has many OH- almost-neighbours, so instead of a chain to one particular ion, it's more a a surrounding by neutralizing ions. But the net effect of polarized and oriented solvent molecules is that the ion charge isn't bare; the vicinity of solvent molecules poles reduces the local charge much and stabilizes the ion.

 

In an "ionic" crystal, say NaCl, each Na+ is surrounded immediately by many Cl-, so that any charge acts over a tiny distance, and the energy of the electric field is small. Here neither, ions are isolated - a situation that would have demanded much energy as you noticed. In a crystal, ions and their orbitals touch an other, so that I even wonder whether it makes sense to tell if the electrons have passed from one atom to the other.

 

Let's see what chemists say.

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Thank you very much for your answers, guys.

 

A guy said to me that "the Mg2+ ion is not unstable, least not in solution. It is it's favored oxidation state which is why all natural forms of Mg involve it being in the +2 state".

 

Ok, i think what he said is Mg2+ is not unstable because he has eight electrons in valence shell. yet he is charged(2+) so if there is in the solution anions i believe he will react with this anions. I just don't understand this part: "at least not in solution" and what means "favored oxidation state".

Edited by amanda.castro

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At normal temperature, isolated ions don't form in significant amount. They attract electrons to neutralize.

 

In a polar solvent, especially water, ions can separate from the carriers of the opposite charge. Thanks to its polarization, water permits the cations and anions to coexist. Though, it needs willing anions: magnesium chloride is soluble, the oxide isn't.

 

Two electrons because this is magnesium's valence. With simple atoms (not transition metals), the outermost shell participates in chemical reactions, the deeper ones don't. Well, that would be if chemistry were simple; for instance xenon can make compounds despite its complete outer shell. Also, many elements have several valences, like 2 and 4 for carbon.

 

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I wrote "I wonder whether it makes sense to tell if the electrons have passed from one atom to the other" and yes, it makes sense.

 

Anions and cations in a solid use to touch an other so that one can't tell whether the electrons in between pertain to one or the other atom, but it makes a difference nearer to the nuclei. And in a solid, anions and cations do carry a charge, as ceramic capacitors show. The displacement of Ba2+ or Zr2+ between two positions in (Ba, Zr)TiO3 induces a charge flow at the capacitor's terminals, so Ba and Zr don't displace as many electrons as protons.

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