Question

Draw electron dot structures for each of the following:
(a) MgCl₂
(b) CaO
(c) NaCl

Answer 1

(a) Magnesium has two valence electrons and chlorine has seven valence electrons. Hence, each chlorine atom gains one electron from the magnesium atom to complete its octet. This leads to the formation of two Cl⁻ ions and one Mg²⁺ ion. The electron dot structure of MgCl₂ is given below:

$\underset{\mathbf{.}\mathbf{.}}{\overset{\mathbf{.}\mathbf{.}}{\mathbf{:}\mathrm{Cl}\mathbf{·}}}+\stackrel{\mathbf{.}\mathbf{.}}{\mathrm{Mg}}+\underset{\mathbf{.}\mathbf{.}}{\overset{\mathbf{.}\mathbf{.}}{\mathbf{·}\mathrm{Cl}\mathbf{:}}}\to {\left[\mathrm{Mg}\right]}^{2+}{\left[\underset{\mathbf{.}\mathbf{.}}{\overset{\mathbf{.}\mathbf{.}}{\mathbf{:}\mathrm{Cl}\mathbf{:}}}\right]}_2^{-}$

(b) Calcium has two valence electrons and oxygen has six valence electrons. So, the oxygen atom gains two electrons from the calcium atom to complete its octet and forms ionic compound CaO. The electron dot structure of CaO is given below:
$\mathrm{Ca}\mathbf{:}+\stackrel{\mathbf{.}\mathbf{.}}{\mathbf{:}\mathrm{O}\mathbf{:}}\to {\left[\mathrm{Ca}\right]}^{2+}{\left[\underset{\mathbf{.}\mathbf{.}}{\overset{\mathbf{.}\mathbf{.}}{\mathbf{:}\mathrm{O}\mathbf{:}}}\right]}^{2-}$

(c) Sodium has one valence electron and chlorine has seven valence electrons. To complete their respective octets, sodium transfers its valence electron to the chlorine atom. The electron dot structure of NaCl is given below:

$\mathrm{Na}\mathbf{·}+\underset{\mathbf{.}\mathbf{.}}{\overset{\mathbf{.}\mathbf{.}}{\mathbf{·}\mathrm{Cl}\mathbf{:}}}\to {\left[\mathrm{Na}\right]}^{+}{\left[\underset{\mathbf{.}\mathbf{.}}{\overset{\mathbf{.}\mathbf{.}}{\mathbf{:}\mathrm{Cl}\mathbf{:}}}\right]}^{-}$