Do nonmetals prefer to receive electrons in chemical reactions?

Yes in general elements which are less metallic in character are going to want to "receive" electrons in order to fill their valence shell. Why do you think this is?

Think about the electron configuration of the for each element as you go across a period on the periodic table. As we move to the right, we are adding orbitals to the atoms, and filling these orbital with electron.

And by the octect rule, most atom will want to fill their valence shell.

Let's consider an atom of elemental calcium, #Ca#, with a valence shorthand configuration of:

#Ca=# #1s^2 2s^2 p^6 3s^2 3p^6 4s^2#

(now remember that the valence electron are the one within the orbital shell with highest principle quantum number #n#, so #4s^2# is the orbital which contain our valence electron for Calcium)

Now consider an atom of elemental oxygen, with a valence shorthand configuration of:

#O=# #1s^2 2s^2 2p^4#

Now let's think about what these two atom could do with their valence shells, in regards to becoming more stable.

Both are just two electron away from having a noble gas electron configuation (which is incredibly stable), and speficially from becoming isoelectronic to either Neon (for oxygen) or Argon (for calcium).

So let's think... in a chemical reaction betwen these two atoms element, what do you think might happen?