Question

What is the Lewis dot structure of $\text{Mg}{{\text{F}}_{\text{2}}}$?

Answer 1

Hint: To draw the electron dot diagram of $\text{Mg}{{\text{F}}_{\text{2}}}$, we need to find the number of valence electrons that take part in bonding and the number of unshared pairs of electrons in the outermost shell of each atom. Then using dots, we can represent valence electrons around each atom to obtain a Lewis dot structure.

Complete answer:
Every element has a specific number of electrons present in its atomic orbitals. Out of these electrons, only those participating in bond formation with another atom which is present in the outermost shell of the atom. These electrons which are present in the outermost orbital of an atom are called valence electrons.
Any atom forms a bond with another atom to attain stability by completing its octet. And it is not necessary that each electron present in the valence shell takes part in octet formation. In some cases, it has been observed that one or more pairs of electrons in the valence shell remain unshared during bond formation. Such pairs of electrons in the outermost shell of an atom that remains unshared are known as lone pairs of electrons.
$\text{Mg}{{\text{F}}_{\text{2}}}$ is an ionic compound made up of magnesium cation and fluoride anion. To draw the electron dot or Lewis diagram of this compound, we first need to write the electronic configuration of atoms.
\[\begin{align}
  & \text{Electronic configurations:} \\
 & \text{Mg : 1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{3}{{\text{p}}^{\text{0}}} \\
 & \text{F : 1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{5}}} \\
\end{align}\]
The magnesium has a total of 2 electrons in its valence shell out of which two electrons will be transferred completely to form an ionic bond with two fluorine atoms having 7 valence electrons each and form a $\text{Mg}{{\text{F}}_{\text{2}}}$ molecule. By donating two electrons, magnesium will have a complete octet in its outer shell and since fluorine is just one electron deficient to complete its octet, two fluorine atoms will combine with magnesium to form a stable $\text{Mg}{{\text{F}}_{\text{2}}}$ compound. The formation of an ionic bond takes place as shown below.

Hence, the electron dot diagram of $\text{Mg}{{\text{F}}_{\text{2}}}$ is:

Note:
The octet rule is always followed during bond formation. According to this rule, every atom tends to attain 8 electrons in its outermost shell. But there is an exception in small atoms like hydrogen. Hydrogen can only attain up to 2 electrons in its valence shell.