Question

Is $HCl$ an ionic salt or covalent molecule?

Answer 1

The two important categories of chemical bonding ionic bonding and covalent bonding. In ionic bond, the complete transfer of electrons take place and are formed due to the electrostatic force of attraction between two oppositely charged ions whereas the covalent bonds are formed by mutual sharing of electrons between the combining species.

Complete answer:
First, the given compound i.e., $HCl$ is an acid and not a salt because when dissolved in aqueous solution, the $HCl$ molecule completely dissociates into respective ions to give ${{H}^{+}}$ and $C{{l}^{-}}$ ions and due to the presence of hydrogen ion, the given molecule is an acid.
Further, the capability of two compounds to form a covalent bond or an ionic bond completely depends on the electronegativity of the atoms bonded together. That means the difference in electronegativity between two atoms can determine the bond type of the molecule as per following data.

Electronegativity difference	Bond type
Greater than 1.7	Ionic bond
Between 1.7 and 0.4	Polar covalent bond
Less than 0.4	Non polar covalent bond

For the given molecule, the electronegativity difference can be calculated as follows:
Electronegativity of hydrogen $=2.20$
Electronegativity of chlorine $=3.16$
Electronegativity difference for the molecule $=3.16-2.20\Rightarrow 0.96$
Hence, the electronegativity difference for $HCl$ molecule is 0.96 and as per the data given in table, if the electronegativity difference lies between 1.7 and 0.4, then the molecule is polar covalent molecule. Thus, we can conclude that the given molecule i.e., $HCl$ is a polar covalent molecule.

Note:
It is important to note that the electronegativity difference between hydrogen and chlorine in $HCl$ molecule is less than 1, so it is not a true covalent compound as because of bond polarity and higher electronegativity of chlorine atom, the shared pair of electrons always form an electron cloud over chlorine atom forming partial positive and partial negative charge on hydrogen and chlorine atom respectively. Hence, the $HCl$ is a covalent molecule with $17$ ionic character.