Answer
If the electronegativity difference between bounding atoms is less than 1.7 then the bond has a more covalent character. The electronegativity difference between Al and Cl is 1.55. Hence, the aluminium chloride in the solid-state will has a significant covalent character
Step-by-step explanation
There are 3 ways by which aluminium chloride in the solid-state has significant covalent character that can be explained:
It can be explained in terms of ionization energy, Fajan rule, and electronegativity difference.
Al has very high ionization energy and for Cl, it's not easy to withdraw 3 electrons from Al’s outermost shell because Cl is not enough electronegative. Therefore, rather than Al losing 3 electrons, it shares its electrons with 3 Cl⁻ ions, and when electrons are shared with 2 atoms; a covalent bond is formed.
Fajan’s rule:- According to Fajan’s rule , the larger the size of an anion; the more covalent will be the bond. So, if we take for example AlCl3 and AlF3, here F⁻ ion is smaller than the Cl⁻ ion, also F has enough electronegative to withdraw Al outermost electrons and therefore AlF3 is ionic but AlCl3 is covalent
Lastly, if the electronegativity difference between bounding atoms is less than 1.7 then the bond has a more covalent character. The electronegativity difference between Al and Cl is 1.55. Hence, the aluminium chloride in the solid-state will has a significant covalent character