If you see where each of the elements are on the table it explains alot. Beryllium is on the far left. Sulfer on the right. The magic number for elements is 8. Elements, most of the time, have an outer electron shell that has 8 spaces. It is most stable when all those spaces are filled with electrons. The less electrons in that outer shell, the less stable.
Beryllium only has 2 in its outer shell. Sulfer has 6. Therefore Sulfer is more stable and will take 1 or 2 electrons from a less stable element like beryllium. And Beryllium has to give them up because it isn't very stable.
It's easiest to think about it like this: Every element wants to be like the inert gasses (far right column) because they are the most stable. But when two elements come in contact the one with the most electrons in the outer shell wins and takes as many electrons as it needs to make itself stable.