Question

What is more covalent ${\text{NaCl}}$ or $AlC{l_3}$ ?

Answer 1

As we know that the covalent character is anything but a proportion of how minimal the bond is energized. In chlorine, the bond electrons are shared similarly between the molecules thus the majority of the bond electron thickness is disseminated equally on the line between the cores. In hydrogen chloride the thickness is one-sided towards the chlorine so the bond is polar and we say it has more ionic character, or less covalent character. At the opposite finish of the range, particles with low polarization/Polarisability will deliver a pure ionic substance, yet a little, exceptionally charged cation will pull an anion's electrons towards it, bringing about huge electron thickness on the line between the cores and we say the security has covalent character.

Complete answer:
Fajans' standard expresses that a compound with low sure charge, huge cation and little anion has ionic bond whereas a compound with high certain charge, little cation and huge anion are covalently fortified.
For high charge, little cation will have seriously polarizing power. Whereas bigger is the size of anion, more will be the polarization of anion. Since, in such a case, this electron haze of anion is more diffused. This makes the anion effectively polarizable. What’s more, this sort of polarization causes the freely holding of electron clouds and electron clouds to shift towards anion to such an extent that they produce covalent character in bond.
Presently in the event of aluminum trichloride Al has $+ 3$ charge in ionic state and its size will be a lot more modest than $Al$ iota just as Na molecule and as it has high certain charge than $N{a^ + }$ particle so it will pulls the electronic haze of all Chloride particles towards itself to such an extent that cloud will be shared because of wave nature of electron and bond will have ionic character as will covalent character.
assuming we supplant $\;Cl$ with Bromine, covalent character of that $AlB{r_3}$ will be bigger than $AlC{l_3}$ because of high Polarisability of Br because of its bigger size that is brought about by frail atomic appreciation for external most electron so electron will be all the more free and all the more handily shared then Chlorine.

Note:
More prominent is the polarization power (capacity of the cation to twist electron haze of the anion) , more noteworthy is its inclination to shape covalent bonds. Higher the charge on the cation higher is the compelling atomic charge which demonstrates the more noteworthy polarization force of the cation. This is the reason $NaCl$ is less covalent than $AlC{l_3}$.
We know that Aluminium trichloride is more covalent than Sodium chloride. In Sodium chloride, Sodium will give one electron to Chloride hence shaping an ionic holding. In$AlC{l_3}$ , Aluminium imparts electrons to chlorine and structures a covalent bond.