Formation of Ammonia Molecule (Pyramidal Stucture)

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Need of Hybridization During Formation of Ammonia Molecule:

  • In nitrogen atom, there are three half – filled 2p orbitals and the valency should be 3 and it is three.
  • These three ‘p’ orbitals are perpendicular to each other and if they form bonds, the angle between them should be 90°.
  • But actual angle between bonding orbitals in ammonia is 107°. To explain this difference in the angle the concept of hybridization is required.

 Electron Configuration:

  • The Atomic number of Nitrogen is 7.  Its configuration in ground state is 1s2, 2s2, 2p3

Formation of Ammonia Molecule 01

Hybridization:

  • In the formation of ammonia one 2s orbital and three 2p orbitals of nitrogen mix up forming four hybrid orbitals of equivalent energy. These four new equivalent orbitals are called sp3 hybrid orbitals.
  • They are identical in all respect. One hybrid orbital has paired electrons (lone pair) and it is nonbonding orbital. Other three orbitals are half – filled and they are bonding orbitals.
  • The nonbonding pair of hybridized orbitals is called as a lone pair.
  • These hybridized orbitals are in the directions of four corners of a regular tetrahedron.

 

Formation of Ammonia Molecule 02

Angle and Geometry of Ammonia Molecule:

  • Four sphybridized orbitals formed, repel each other and they should be directed towards the four corners of a regular tetrahedron and  Angle between them should be 109.5°.
  • One hybrid orbital has paired electrons and it is nonbonding orbital. Other three orbitals are half – filled and they are bonding orbitals.
  • But due to greater repulsion exerted by lone pair on bonding orbitals, the angle is reduced to 107°. Thus ammonia has distorted the tetrahedral shape.
  • The three half filled (containing unpaired electron) sp3 hybrid orbitals of nitrogen overlap axially with three half filled 1s orbitals of three hydrogen atoms separately to form three covalent N-H bonds
  • Hence geometry is tetrahedral pyramidal in which the nitrogen lies at the centre, three hydrogen atoms form base and a one pair of electrons forms the apex of pyramid. H-N-H angle is 107°.

Bonds in Ammonia Molecule:

  • The three half filled (containing unpaired electron) sp3 hybrid orbitals of nitrogen overlap axially with three half filled 1s orbitals of three hydrogen atoms separately to form three covalent N-H bonds (sigma bonds). The fourth hybrid orbital containing lone pair of electron remains non bonded.
  • The bonds between Nitrogen and hydrogen are sp3– s.
  • H – N — H bond angles are 107°.
  • All N-H bond in ammonia are of equal strength.

 



Formation of Ammonia Molecule 03

Type and Geometry of Ammonia Molecule:

 

Name of Molecule Ammonia
Molecular Formula NH3
Type Of Hybridisation sp3
Geometry Pyramidal
No. Of Bonds 3
No. Of Sigma bonds 3 sigma
Bond angle 107°
Overlaps 3 sp3 – s
Bonds 3 N-H
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