Here's why:
* Sulfur's electron configuration: Sulfur has 16 electrons. Its electron configuration is 2-8-6. This means it has 6 electrons in its outermost shell.
* Octet rule: Atoms tend to gain or lose electrons to achieve a stable configuration with 8 electrons in their outermost shell (the octet rule).
* Gaining electrons: Sulfur can achieve a stable octet by gaining 2 electrons. This gives it a -2 charge, making it a sulfide ion (S2-).
