Question

Consider NH3 and PH3. Electronegativities: P = 2.1, H = 2.1, N=3.0. Which statement is false?

The bond dipoles in NH3 are directed toward the nitrogen atom. For PH3 there is no bond dipole moment.

Both molecules are polar.

There are no false statements. All of these statements are correct.

Both are sp3 hybridized at the central atom.

The P-H bonds are more polar than the N-H bonds.
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Answer 1

The P-H bonds are more polar than the N-H bonds.

Step-by-step explanation:

Phosphine is a polar molecule with non-polar bonds. The phosphorus atom is bonded to three hydrogen atoms and the phosphorus atom has a lone pair of electrons. Since hydrogen and phosphorus are equal in electronegativity, it implies that they attract the shared pairs of electrons the same amount,hence bonding electrons are shared equally making the covalent bonds non-polar.

The lone pair of electrons on phosphorus causes the molecule to be asymmetrical with respect to charge distribution this is why the molecule is polar even though the are non-polar bonds in the molecule.

Looking at the values of electro negativity stated in the question, one can easily see that the difference in electro negativity between nitrogen and hydrogen is 0.9 while the difference in electro negativity between phosphorus and hydrogen is zero. It is clear that NH3 is naturally more polar than PH3 since each individual N-H bond in NH3 is a polar bond while the individual P-H bonds in PH3 are nonpolar.