Lets Form bonds
Al=2,8,3
Lets Write actual configuration or modern
[tex]\\ \sf\longmapsto 1s^22s^22p^63s^3[/tex]
Cl:-2,8,7
Let's write configuration
[tex]\\ \sf\longmapsto 1s^22s^22p^63s^23p^5[/tex]
Now Criss cross valency (Refer to attachment)
We get
[tex]\\ \sf\longmapsto AlCl_3[/tex]
