Arsenic, As: atomic number is 33. So its electron configuration is:
As:[Ar]4s2 3d10 4p3
Antimony, Sb: atomic number is 51, so its electron configuration is:
Sb: [Kr] 4d10 5s2 5p3.
As you see, the last shell of both element has two s and 3 p electrons.
The electrons in the last shell are responsible for most of chemical behaviors, because those are the electrons that interact in the chemical changes.
