Question

What is the net charge of the ionic compound, rubidium sulphide?

Answer 1

Hint: Ionic compounds are formed between a metal and a non – metal. Their formation consists of ionic bonds that are formed by transfer of electrons from the metal to the non – metal. The transfer of these charges makes the molecule neutral. Rubidium sulphide has the formula, $R{{b}_{2}}S$.

Complete answer:
We have been given an ionic compound rubidium sulphide, to find its net charge. An ionic compound consists of a cation that donates electrons and an anion that gains electrons. They form an ionic bond in such a way that the charge on both of them becomes neutral and hence the atom exists.
When any compound exists as an ion, it possesses some charge, but in the form of a compound the net charge is always zero. This can be proved by taking out the individual charges on rubidium and sulphide, and taking out their sum, which will be zero.
Rubidium consist of 1 electron in its valence shell, so it exist as $R{{b}^{+}}$ion, while, sulphide is the sulphur ion with a charge of negative 2, as ${{S}^{2-}}$ . Thus, in order to balance a -2 charge of sulphide, rubidium will be taken in a quantity of 2 atoms as $2R{{b}^{+}}$, then they will form the compound rubidium sulphide with formula, $R{{b}_{2}}S$. Charge of Rb is +2 and that of S is -2, so taking their sum we have,
Net charge = +2 – 2
Net charge = 0
Hence the net charge on rubidium sulphide, $R{{b}_{2}}S$is 0.

Note:
The fact that the net charge is 0 on any neutral molecule is used to predict the oxidation states or the charges of any atom in a molecule. This also explains the electrical neutrality of a molecule. As any molecule does not have free electrons in its neutral state.