Question

How many chloride ions would combine with an $A{l^{3 + }}$ ion to form aluminium chloride?

Answer 1

Hint: We need to understand the valency concept of elements to form chemical bonds. Valence electrons are electrons present in the outermost shell of an atom. Atoms lose or gain these valence electrons which leads to chemical bonding. Also, the attractive force which holds various constituents such as atoms and ions together in different chemical species is called a chemical bond. To form a stable chemical compound, the charge on the atoms must also be neutralized along with the satisfaction of the valency.

Complete step by step answer:
We know that to form an ionic compound, the charges of the constituent atoms must be neutralized. Atoms gain or lose electrons to form chemical bonds. Electrons are negatively charged particles hence when an electron is removed from an atom, it acquires a positive charge. In the given case, the Aluminium has a positive charge which means it is electron deficient. Hence to combine with other atoms, it needs to neutralize its positive charge.
The given ion is $A{l^{3 + }}$ which has a $ + 3$ charge. Hence it requires three electrons to form a stable compound. Such bonds are called ionic bonds. Therefore, to neutralize its $ + 3$ charge, it will attract three electrons from atoms which have $3$ electrons extra, that is they have a $ - 3$ charge.
Since the given compound is Aluminium chloride, chloride ions have a -1 charge hence aluminium will need three such ions. Thus $A{l^{3 + }}$ ion needs three chloride ions to form aluminium chloride as $AlC{l_3}$.

Note: It must be noted that elements crave to neutralize their charge in order to satisfy their valency and complete their octet. Main group elements tend to bond in such a way, either by losing, gaining or sharing electrons such that each atom has 8 electrons in its outermost (valence shell). This craving of elements to satisfy its octet is the main reason for the chemical bonding. For example, in $AlC{l_3}$, each of the atoms have a complete octet that is 8 electrons in their outermost shells.