The definition of an ion - Totally confused with this basic concept

[scilearner]

Hello everyone,

 

I'm confused with the definition of an ion. Does an ion mean an atom that has lost or gained an electron or an atom that has the potential do so.

 

For example

 

Na+ + Cl- --------- NaCl

 

In this case doesn't Na+ mean it has a potential to lose an electron. I mean NaCl would be formed if this happens. But if we write Na+ at the start doesn't it give the impression that Na+ has already lost an electron.

 

2nd example

 

NH3 + H+ ---------- NH4

 

In this doesn't H+ mean it has already lost an electron (not has the potential to). Then acid base reaction occurs to form NH3

 

Can you understand my point isn't it bit inconsistent the definition of an ion because sometime it means it has the potential to lose electrons.

 

Any help on this would be greatly apprecitated.

[frosch45]

An ion simply means that an electron(s) has been lost or gained by an atom. For example, Na+ is an ion of Na, Cl- is an ion of Cl

 

In this case doesn't Na+ mean it has a potential to lose an electron. I mean NaCl would be formed if this happens. But if we write Na+ at the start doesn't it give the impression that Na+ has already lost an electron.

 

when you write Na+, it implies that Na has lost an electron already to the Cl- atom. This usually happens when a solid dissociates in a liquid, for example when NaCl dissociates in water, it forms a solution with water, Na+ ions, and Cl- ions. Once NaCl has formed, however, the Na has effectively lost its electron to Cl, but this is resultant of the bond, so it is written together. A picture of the lattice structure of NaCl may also be worth a gander.

 

Can you understand my point isn't it bit inconsistent the definition of an ion because sometime it means it has the potential to lose electrons.

 

I wouldn't call it inconsistant, a better definition of an ion is electron(s) have been lost or gained by an atom

[scilearner]

Thanks a lot for your help frosch45 . I had a think about what you have said and it makes sense. Now however I have few more questions

 

Is an ion stable or not?

 

Ion's have stable valence outershell hence I think they are stable. So why do they react to form NaCl. Is it simply because unlike charges attract and not actually to be stable. I mean if Na+ exist by itself is it fair to say it is stable.

 

My other questions is how can a solution of NaCl dissocitae to Na+ and Cl-. Wouldn't they attract like magnets forming NaCl again.

[Klaynos]

It depends what you mean by "stable".

 

Ions are charged so they interact strongly with other charged particles, as well as +ve ions wanting to try and capture an electron a -ve ion will loose an electron very easily as they are not very well bound.

[jdurg]

I wouldn't call it inconsistant, a better definition of an ion is electron(s) have been lost or gained by an atom

 

To be safest, I wouldn't just say "an atom" because NH4+ is an ion and NH4 is not an atom.

 

A better definition is any "species" (Where "species" is either an atom, or a molecule) in which the number of electrons do not equal the number of protons in that species, resulting in a charge of some type existing. Therefore, NaCl is not an ion because the number of electrons is equal to the number of protons. Na+ and Cl- are both ions since the electrons =/= the protons.

 

A lone ion is inherently unstable. Any charged partcle is inherently unstable and will do what it can to balance out that charge. Hence why Na+ and Cl- "bind" together to form NaCl. When in water, the ions are able to separate from each other due to the properties of water, but overall the charge is still balanced.

[frosch45]

My other questions is how can a solution of NaCl dissocitae to Na+ and Cl-. Wouldn't they attract like magnets forming NaCl again.

 

 

What happens when NaCl dissolves in water is that the Na+ gets surrounded by the oxygen atoms (water) and the Cl- gets surrounded from the hydrogen atoms (water). So in effect, whats happening is your water molecules are ripping apart the ionic structure and getting in the way of that Na-Cl bond.

 

http://gold.cchem.berkeley.edu/Pictures_and_Images/NaCl.jpg

 

In this picture, the teal blue sphere represents the Cl, and the brighter blue represents the Na. Notice how the hydrogen (gray) surrounds the Cl ion and the oxygen (red) surrounds the sodium.

 

 

This is a great great video that explains everything very well, but be patient because it takes several minutes to load.

 

http://yteach.co.uk/page.php/resources/view_all?id=salt_acid_base_water_reaction_product_reactant_precipitation_thermal_decomposition_page_1&from=search

[scilearner]

Thanks everyone who has helped :-):-) . I think I'm getting it now. I still got few more questions.

 

So when the water pulls apart the molecule to ions and the water surround these ions, how can they react again?

 

This equation is from the top of my head so might not be right. I hope you get the idea though

 

Example of what I'm talking about

 

NaCl (aq) + KI (aq) react. The products would be NaI and KCl. Why does Na react with I why can not it just recombine with Cl and not take part in a reaction. I mean if all the ions in this reaction are surrounded by water molecules how can they react?

 

Why does Na+ choose I- rather than Cl-

 

Why can not an ion exist by itself?

 

Is this because the atom does not have another atom to lose or gain nessecary electrons to be an ion. Is this role of the spectator ions. Helping the atoms required to be ions. Am I right?

 

@ frosch45

 

The video was great . Good references Thanks

[Kyrisch]

It has to do with energy. The whole reason ionic bonds forms is because their products are more stable, or have less chemical energy contained in the bond. So, NaCl + KI --> NaI and KCl because these two compounds have stronger (less energetic, more stable) bonds than the reactants.

[jdurg]

In reality, however, what you wind up with is a mixture of NaCl and KI when the "reaction" is done. As the water evaporates, whatever is closest to the Na+ ion will bond with it whether it's Cl- or I-. Granted, there is some small preferences due to ion size and other "stuff", but it's not like when AgNO3 and NaCl are mixed.