The molecules BF₃ and NF₃ are both covalent compounds,
but BF₃ is non polar whereas NF₃ is polar. The reason for
this is
(a) atomic size of Boron is larger than nitrogen
(b) Boron is metal while nitrogen is gas
(c) B – F bonds are non-polar while N – F bonds are polar
(d) BF₃ is planar but NF₃ is pyramidal
Answers
c) B – F bonds are non-polar while N – F bonds are polar is the correct answer
Let us solve for it
Explanation:
Polarity
• The hetro-atomic molecules (having different types of atoms in them) when sharing of electrons occur the shared pair do not lie in middle, it gets displaced towards more electronegative atom.
The polarity is measured as Dipole moment .
This dipole moment depends upon many factors : Out of which geometry is also one of the factor .
In Boron tri- Fluoride , the geometry is Planar as shown below : In it the dipoles of 3 B-F bond align towards F(because F is more electronegative than B ) Therefore they cancel each other whereas in N-H bond ,the vectors are in directed towards N (as N is more electronegative than H )therefore the three vectors add up and align in one direction that is in the direction of lone pair and the vectors add up to give resultant dipole .
In boron trifluoride the vectors cancel each others effect due to planar structure .
The geometry of both is given below :
