Čapek is spelled with a Czech "C" that has a hook over the top. The c hook sound is like "ch" in "cheap."
Czapek is the way the name was spelled in old Czech language. The "z" takes the place of the c or č (c with hook).
The female form of Čapek is written as Čapkova. Notice that in the female form, the "e" in the middle is removed. In Czech the "e" is often dropped when -ova (the female form of name) is added. Another example can be the surname Jelinek - Jelinkova, Masek - Maskova.
Listen to Blanka Lednická as she pronounces Čapek and Čapkova: