Oxygen, sulphur, selenium, tellurium and polonium are all members of group sixteen. The elements in group sixteen all possess six electrons in their outermost shell. Recall that an atom is said to stable if it contains eight electrons in its outermost shell. This is also referred to as the octet rule. Hence atoms of elements obey the octet rule when they combine to form compounds with eight electrons present on the outermost shell of each atom.
Having six electrons on their outermost shell implies that they need to gain two electrons by bonding to other atoms of other elements. Two examples will suffice here.
Water is formed when an oxygen atom shares an electron with each hydrogen atoms.
Hydrogen sulphide is formed when sulphur share two electrons with two hydrogen atoms. Hence the answer.
In this case, when chemical bonds are formed, the valence electrons are the bridge to make it possible, nevertheless, the octet is the limit for the formation of bonds, that is, an element must not exceed 8 shared or gained electrons. In such a way, elements able to gain to electrons to attain the octet are those from the VIA group: O, S, Se, Te, Po, as they have six valence electrons, so two more electrons are suitable for attaining the octet.
