Does high electronegativity mean low electropositivity?

  • #1
I understand that electronegativity and electropositivity are opposite terms, but does being high in one mean you are low in the other?

I saw that HCl will react with NaCl to create Cl2 and NaH. I believe that Cl has the greatest electronegativiy (willingness to attract an electron). So wouldn't it stay bonded to H and Na, which are less electronegative (assuming that means H and Na are more electropositive)?

So why does Cl bond to the other Cl? Does it have to do with the type of bond or some other factor in this reaction, and if so, is there an order of operations to consider when determining whether a reaction will occur (e.g. 1. bond type, 2. electronegativity, 3. etc.)?
 
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  • #2
Borek
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I understand that electronegativity and electropositivity are opposite terms, but does being high in one mean you are low in the other?

By definition they reflect opposite properties so yes, that's what I would expect. But while I have seen quantitative definition of the electronegativity (actually several definitions, wikipedia lists at least some them), I don't think I have ever seen a definition of electropositivity. Probably one can be easily proposed by extending the ideas already used with the electronegativity, but my bet is electropositivity is such an obscure term it is not worth it.

I saw that HCl will react with NaCl to create Cl2 and NaH.

Will it? I haven't seen such a reaction.
 
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  • #4
Borek
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Looks to me like an automatically created database of everything, having nothing to do with the reality.
 
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  • #5
Looks to me like an automatically created database of everything, having nothing to do with the reality.
:cry:I guess studying using the internet doesn't work, which is why talking to a real person is really helpful.
Anyways, thanks for all your help!:biggrin:
 
  • #6
So, just to be clear. Is there no reaction between HCl and NaCl? How can I know if a reaction will occur?

Is there any disassociation or maybe transfer of Cl- ions between HCl and NaCl?


If the answer is no reaction, then can we assume Cl2 + NaH will result in HCl and NaCl? How can we know if this reaction will occur?
 
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  • #7
Borek
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So, just to be clear. Is there no reaction between HCl and NaCl?

No reaction for all practical purposes.

How can I know if a reaction will occur?

This is more or less what chemists learn - how to predict what will/can happen. No shortcuts, you need to accumulate a lot of knowledge (and even then you will be occasionally surprised by the reality, there are always many convoluted, interleaved and antagonistic effects affecting the final outcome).

Is there any disassociation or maybe transfer of Cl- ions between HCl and NaCl?

When you dissolve both they dissociate, Cl- from both sources are identical and there is no way which came from which compound.

If the answer is no reaction, then can we assume Cl2 + NaH will result in HCl and NaCl? How can we know if this reaction will occur?

See above - it is not trivial and may depend on conditions. HCl and NaCl seem to be the most likely outcome, as these are very stable compounds (and stability of products is always one of the main driving forces responsible for the reaction outcome).
 
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  • #8
Got it! Thanks again :bow:

Is there anywhere you can go to see a list of 'known' reactions between compounds? Like the website I found before, but with real reactions...
 
  • #9
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See above - it is not trivial and may depend on conditions. HCl and NaCl seem to be the most likely outcome, as these are very stable compounds (and stability of products is always one of the main driving forces responsible for the reaction outcome).
Depending on ratio of reactants, though.
If Cl2 is in excess then, yes, NaCl+HCl, because neither of them reacts with Cl2.
If, however, NaH is in excess then NaH does not react with NaCl, but readily reacts with HCl:
NaH+HCl=NaCl+H2
total
2NaH+Cl2=2NaCl+H2
 
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  • #10
Borek
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Depending on ratio of reactants, though.

Good point.

And a good example of why it is often difficult to precisely predict what will really happen without taking into account thousands of details.
 
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  • #11
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Is there anywhere you can go to see a list of 'known' reactions between compounds?

That would be a very long list and it would never be complete. But typical reactions are usually listed in sources for the individual compounds (e.g. chemistry textbooks or Wikipedia). For example the French Wikipedia entry for NaH includes the above mentioned reaction with HCl.
 
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