Question

The electronegativity is 2.1 for H and 1.9 for Pb. Based on these electronegativities, PbH4 would be expected to... (Why is the correct answer "a" if Pb is a metal? Covalent bonds can't contain metals...)

a) have polar covalent bonds with partial negative charges on the H ions.

b) be ionic and contain H+ ions.

c) have polar covalent bonds with partial positive charges on the H atoms.

d) be ionic and contain H- ions.

Answer 1

1. If the electronegativities are equal (i.e. if the electronegativity difference is 0), the bond is non-polar covalent
2, If the difference in electronegativities between the two atoms is greater than 0, but less than 2.0, the bond is polar covalent
3. If the difference in electronegativities between the two atoms is 2.0, or greater, the bond is ionic

From the above rules, the bonds between Pb and H in PbH4 will be polar covalent. Since H is more electronegative it will pull electron charge toward itself and will be negative.