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How to find hybridisation.and hybridisation of NH3 the most important hybridisationof group 15th elements .explanation

How to find hybridisation.and hybridisation of NH3 the most important hybridisationof group 15th elements .explanation

Grade:12

1 Answers

Ashutosh Mohan Sharma
askIITians Faculty 180 Points
6 years ago
Ammonia (NH3), or, more accurately, the central atom in ammonia, issp3hybridized. Here's how you'd go about determining this.

First, start withNH3'sLewis structure, which must account for8valence electrons-5from nitrogen and1from each hydrogen atom.


As you can see, all thevalence electronsare indeed accounted for - 2 for eachcovalent bondbetween nitrogen and hydrogen, and 2 from the lone pair present on the nitrogen atom.

Now, here is where it gets interesting. Nitrogen's energy levels look like this.


Looking at this energy diagram, one could see that each of the threep-orbitalsis available forbonding, so why would the atom need to be hybridized? Here's where stability and geometry come into play.

If the three hydrogen atoms would bond with nitrogen using the availablep-orbitals, the bond angles would be90°. However, this cannot take place since electron-rich regions must be located as far away from each other as possible in3Dspace - this is why the bond angle in ammonia is approximately107°.

Moreover, the hybrid orbitals would ensure the formation of a stronger bond with the hydrogen atoms, since hybrid orbitals formed fromsandp-orbitalshave a greater electrondensityon one side of the lobe - the side that bonds with the hydrogen atom.

Molecule stability also come into play, since thesp3hybrid orbitals will be lower in energy than the three unhybridizedp-orbitals.

So, in order to determine hybridization, you must determine the central atom'ssteric number, which represents the number of electron-rich regions around the atom.

Since it forms 3 covalent bonds and has 1 lone pair, nitrogen'ssteric numberwill be equal to4, which implies that onesand threep-orbitalswill combine for a total of4hybridized orbitals.509-1458_nh3_lewis.gif509-740_85dd4f3d971652db5815158eabdc3d47.png

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