Why does NH3 turn into NH4+? Also question about bond EN.

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In summary, the conversation covers the stability and bonding of atoms, specifically in regard to NH3 and PH3 forming ammonium and the difference between ionic and covalent bonds. It is also mentioned that ammonium can exist as an ionic compound in water but is primarily found as NH3 and H+. The conversation delves into the geometry of NH3 and how the addition of a proton allows for a more stable tetrahedral shape. The experts also clarify that the trigonal pyramidal shape is less stable than the tetrahedral shape.
  • #1
Hammad Shahid
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Hi guys.
So I know that atoms bond to obtain stability / full octet.
But my question is that NH3 is already stable and each N and H has a full octet. So why does ammonium form? I know that an H+ is attached so no e- are added, but why is there a need for this change?
Same question for PH3 -> PH4+, and other such cations.

Another question I have is that where do we draw a line between an ionic or covalent bond?
Past what electronegativity difference is a bond considered ionic and why?

Thanks you. I only have basic level understanding in chemistry so sorry if these questions are too simple.
 
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  • #2
Consider ammonia dissolved in water, it exists and is a cleaning product available in your local supermarket or similar.
Technically it is ammonium hydroxide in that state, but still it is NH3
 
  • #3
rootone said:
Consider ammonia dissolved in water, it exists and is a product available in your local supermarket or similar.
Technically it is ammonium hydroxide in that state, but still it is NH3
Hm ok so NH3 (aq) is NH4OH? Okay, so then NH4+ can’t exist as free ions though right? It will be NH3 and H+ in water technically?
 
  • #4
What I mean is that ammonium can form an ionic compound with other elements as long as it’s in water and then the solute precipitates, is that correct? Otherwise in water it’s as NH3 and H+?
 
  • #5
N with 5 valence electrons bonds with three H to complete the shell. However NH3 has a geometry problem. 3 of the 5 electrons are in covalent bonds with Hydrogen and two aren’t, there is no symmetric way to arrange these. The electrons in the bonds and the remaining two valence electrons all repel as much as possible. As a result the three bonds bend out of plane making something like a three legged stool and the other two electrons hang out more on top of the stool. It is this broken symmetry that allows a fourth bond. Despite the canonical 8 electrons the screening still can’t be symmetric. There is too much electron probability on top and that attracts another proton.

Now with 4 H bonds the molecule can arrange in a perfectly symmetric tetrahedron. There is no concentration of electron probability anywhere,
 
  • #6
@Cutter Ketch Oh ok that makes a lot of sense. The proton stabilizes the polarity then. Also, does that mean that the trigonal pyramidal shape is less stable than tetrahedral in general?
 
  • #7
Hammad Shahid said:
@Cutter Ketch Oh ok that makes a lot of sense. The proton stabilizes the polarity then. Also, does that mean that the trigonal pyramidal shape is less stable than tetrahedral in general?

Yes.
 
  • #8
Cutter Ketch said:
Yes.
Thank you.
 

1. Why does NH3 turn into NH4+?

NH3 (ammonia) can turn into NH4+ (ammonium) through a process called protonation. This occurs when a proton (H+) is added to the NH3 molecule, resulting in the formation of NH4+. This protonation reaction typically happens in aqueous solutions due to the presence of water molecules, which can act as a proton donor.

2. What is the chemical equation for the conversion of NH3 to NH4+?

The chemical equation for the conversion of NH3 to NH4+ is: NH3 + H+ → NH4+. This equation represents the addition of a proton (H+) to the NH3 molecule, resulting in the formation of NH4+.

3. Why is NH4+ a positively charged ion?

NH4+ is a positively charged ion because it has gained a proton (H+) through the protonation process. This extra proton gives the NH4+ ion a positive charge, making it a cation.

4. How does bond EN (electronegativity) play a role in the conversion of NH3 to NH4+?

Bond EN (electronegativity) plays a crucial role in the conversion of NH3 to NH4+. The addition of a proton (H+) to the NH3 molecule results in the formation of a polar covalent bond between the nitrogen (N) atom and the hydrogen (H+) atom. This is because nitrogen has a higher electronegativity value than hydrogen, causing it to attract the shared electrons more strongly and resulting in a slight negative charge on the nitrogen atom and a slight positive charge on the hydrogen atom. This polar covalent bond allows for the formation of NH4+.

5. Why is the conversion of NH3 to NH4+ important in biological systems?

The conversion of NH3 to NH4+ is important in biological systems because it is a vital step in the process of nitrogen fixation. Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into a form that can be used by plants and other organisms to build proteins and other essential molecules. The conversion of NH3 to NH4+ is also important in maintaining the pH balance in living organisms, as it is a common way for excess protons (H+) to be removed from cells and tissues.

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