Question

How can we use the valence electrons and the octet rule to predict the charge an element will obtain.

Answer 1

Valence electrons are the outer shell electrons that participate in the formation of the chemical bond. The octet rule states that atoms always tend to lose, gain, or share electrons to achieve the electronic configuration of the nearest inert gas.

Complete step-by-step answer: In the periodic table, Noble gases are known to be the most stable gases. They are also called as inert gas as they are highly unreactive due to their stable electronic configuration. The general electronic configuration of Noble gases is ${\text{n}}{{\text{s}}^{\text{2}}}{\text{n}}{{\text{p}}^6}$ except ${\text{He}}$(${\text{n}}{{\text{s}}^{\text{2}}}$).
All other elements in the periodic table are reactive due to their unstable electronic configuration. These elements always try to achieve a stable inert gas configuration. This can be explained by the octet rule. The octet rule states that depending on a number of valence electrons, atoms tend to lose, gain, or share their valence electrons to fully fill their octet. The electrons present in the outermost orbital of an atom are known as valence electrons. We can use the valence electrons and the octet rule to predict the charge of an element as follows:
Atoms having more than 4 valence electrons always tend to gain electrons to complete their octet.Atoms having less than 4 valence electrons always tend to lose their valence electrons to complete their octet.Metals tend to lose their valence electrons while nonmetals tend to gain or share their valence electrons. Metals lose their valence electrons and convert into positively charged ions. These positively charged ions are known as cations.
Charge on cation = Number of electrons lose
Eg. Atomic number of ${\text{Na}}$ is 11 so its electronic configuration is
${\text{1}}{{\text{s}}^{\text{2}}}{\text{ 2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{s}}^{\text{1}}}$
${\text{Na}}$ has one valence electron. To achieve a stable electronic configuration it will lose it's one valence electron and will convert into ${\text{N}}{{\text{a}}^{\text{ + }}}$.
Non-metals gain electrons and convert into negatively charged ions. These negatively charged ions are known as anions.
Charge on anions = Number of electrons gain
Eg. Atomic number of ${\text{Cl}}$= 17 , so its electronic configuration is
${\text{1}}{{\text{s}}^{\text{2}}}{\text{ 2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{s}}^2}{\text{3}}{{\text{p}}^{\text{5}}}$
From the electronic configuration of chlorine, we can say that ${\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{5}}}$ are outer shell electrons of chlorine so we can say that there are 7 valence electrons present in chlorine atom. So it will gain one electron and will achieve a stable electronic configuration. So the charge on chloride ion ${\text{C}}{{\text{l}}^{\text{ - }}}$ is -1

Note: Positively charged species is known as cation while negatively charged species known as an anion. Atoms always try to achieve a stable Noble gas configuration. To achieve the stable Noble gas configuration they either lose or gain their valence electron. The number of electrons gained or lost determines the charge on ionic species.