Understanding the Hybridization and Formation of Pi Bonds in Ammonia and Ethyne

In summary, the N atom in NH3 is sp3 hybridized because it has 4 electron pairs, including 1 lone pair. In ethyne, the triple bond is formed by a sigma bond using one 2s electron and two pi bonds using both 2p electrons. This is because the 2p orbitals are no longer symmetric when forming a molecule, and the pi bonds involve an overlap of only px and py orbitals. The 2pz orbital is not involved in the bonding because it is lower in energy and does not overlap with the other orbitals.
  • #1
Clari
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In ammonia, why the N atom is sp3 hybridized and not sp2 hybridized...since there are only 3 bondings...

Also, in ethyne, that is H-C(triple bond)C-H...for the formation of 2 pi bonds, why it is the unhybridized 2px orbital and 2py orbital of each C atom overlap with each other? How about the 2pz orbital?


any help would be appreciated
 
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  • #2
In NH3, there are 4 electron pairs about the N atom - you're omitting the lone pair.

The triple bond in [itex]H-C \equiv C-H [/itex] is basically a sigma bond using one of the two 2s electrons (the other 2s electron is used for the sigma bond with H), and a pair of pi bonds using both of the 2p electrons. Since C has only 2 electrons in the 2p subshell, and since px and py are lower energy orbitals than pz, the pi bonds must involve an overlap of only these orbitals.
 
  • #3
Gokul43201:

but in my textbook, it is said that orbitals in the same subshell is at the same energy level...I am confused now...
 
  • #4
Clari said:
Gokul43201:

but in my textbook, it is said that orbitals in the same subshell is at the same energy level...I am confused now...

For isolated Carbon atoms they do:[itex]2p_{x},2p_{y} & 2p_{z}[/itex] have all the same energy.But when the Carbon atom reacts with nonmetalic elements,like Hydrogen,those orbitals do not behave in the same manner.That's because 2 of them have one electron and the remaining one ([itex] 2p_{z} [/itex]) has none.The 2 orbitals with one electron they "hybridize" with the [itex] 2s [/itex] orbital which has 2 electrons,resulting in 4 hybridized orbitals of smaller energy than the unhybridized [itex] 2p_{z} [/itex].Since it overlaps 3 hybrid orbitals (one [itex]\sigma [/itex] and 2 [itex] \pi [/itex]) with another C atom,it has a triple bond.Since 2 of the bonds are [itex]\pi [/itex],and another 2 are [itex] \sigma [/itex],it id hybridized [itex] sp [/itex].


Daniel.

PS.Maybe Gokul can put it in a more coherent way... :wink:
 
  • #5
As Dexter mentioned, your textbook is right only when it talks about isolated atoms.

However, when a molecule is being formed, the direction along the line joining the atoms breaks the degeneracy (x, y and z are not symmetric anymore; the z direction is the internuclear direction and so, is different from x and y) between px, py and pz.
 
  • #6
A "pz" pi molecular orbital would be along the same axis as the sigma, perhaps this clarifies things a bit more.
 

FAQ: Understanding the Hybridization and Formation of Pi Bonds in Ammonia and Ethyne

What is the formation of 2 pi bonds?

The formation of 2 pi bonds is a type of chemical bonding in which two atoms share two pairs of electrons through overlapping p-orbitals. This results in a double bond between the two atoms.

How are 2 pi bonds formed?

Two pi bonds are formed when two atoms have unhybridized p-orbitals that are parallel to each other and overlap. The two p-orbitals must also be in the same plane to form the pi bonds.

What is the difference between sigma and pi bonds?

Sigma bonds are formed through the overlap of two atomic orbitals, while pi bonds are formed through the overlap of two p-orbitals. Sigma bonds are stronger and more stable than pi bonds.

Can two atoms have more than 2 pi bonds?

Yes, two atoms can have more than 2 pi bonds if they have more unhybridized p-orbitals available for overlapping. For example, in molecules like benzene, there are 6 pi bonds formed between the carbon atoms.

Why are pi bonds weaker than sigma bonds?

Pi bonds are weaker than sigma bonds because they have less overlap between the atomic orbitals, resulting in a lower bond energy. Additionally, pi bonds are more prone to breaking due to their parallel orientation and lack of electron density between the two atoms.

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