Textbook problem 2D. 5

[Jazlyn Romero 1I]

For each pair, determine which compound has bonds with greater ionic character: (a) HCl or HI; (b)CH4 or CF4; (c) CO2 or CS2.

Hi! For part b, at first I thought CH4 was the compound that has bonds with greater ionic character, however, the correct answer was CF4. I am not sure where I went wrong, as I thought that H and C had a greater electronegativity difference. Can someone please explain this? Thanks!

[Crystal Pan 2G]

The electronegativity of H is 2.2, F is 4.0(the most electronegative element), and C is 2.6. The EN difference between C and H is only 0.4 while the EN difference between C and F is 1.4. So CH4 could even be classified as a nonpolar covalent bond, while CF4 would display more ionic character.

[SophiaJenny3I]

The C - F bond actually has a large difference in electronegativity compared to the C - H bond, so CF4 is actually more ionic. In simpler terms, F really wants another electron cause it only needs 1 more to make a complete octet. Also, this is in the 2p shell, so the electrons are really held tightly by the nucleus. It's very electronegative. So, there is a major difference between the electronegativity of C and F. Sometimes it helps to draw it out to see that the C - H bond in the CH4 molecule shares its electrons, so it's covalent. Hope this helps!