Molecule Polarity Arranging?

Question

Arrange the following substances according to increasing polarity.

With Motivation/Justification.

a) PH₃, NH₃, SbH₃, AsH₃

b) Cl₂, HF, H₂O

c) AlCl₃, KCl, Cl₂, PCI₃

_{thanks for any answer in advance!}

Answer 1

a.) SbH₃ > AsH₃ > PH₃ > NH₃ . The electronegativity of the X atom in this XH₃ series determines the polarity of the molecule. Electronegativity increases as you move up a column in the periodic table, therefore the X-H bonds are more polarized as you move up the periodic table.

b.) Cl₂ > H₂O > HF. There are two factors here- the geometry of the molecule and the electronegativity difference between the atoms. Since Cl is bonded to itself there is no polarity. H₂O is polar but the H-O bond is less polar than the H-F bond. Since F is more electronegative than O, the H-F is the most polar.

c.) Cl₂ > AlCl₃ > PCl₃ > KCl. Like the previous example the Cl-Cl bond is not polarized because it contains two Cl atoms with the same electronegativity. KCl is very polar since K is way to the left of the periodic table and electronegativty increases as you move right in the periodic table. Al is to the left of P in the periodic table, so the P-Cl bond is more polar, and thus PCl₃ is more polar than AlCl_3.