Polarizability and Ionic Character

[Victoria Luu - 1C]

How can you use the polarizing power to find which element has more ionic character? What are the general guidelines?

[ChathuriGunasekera1D]

If an ion has more polarizing power, that means that it is able to influence another atom's electron cloud shape. For example, Ca2+ has polarizing power, and can alter the electron cloud of Cl- (or other ions). The smaller the size of the ion, and the larger the charge, the more polarizing power a cation has. Polarizing power applies to cations.

Polarizability applies to anions, because their electron cloud gets pushed around in the presence of a cation. For example, Br- has polarizability because its electron cloud shifts in the presence of Na+ for example.

So if you wanted to strictly use polarizing power, you can only determine the ionic character in a cation. As polarizing power increases, ionic character increases. Likewise strictly using polarizability, as polarizability increases, ionic character of anions increases.

[EllerySchlingmann1E]

It definitely depends on which kinds of elements and ions you want to talk about when discussing polarizing power. As mentioned above, polarizing power describes a cation's ability to create a dipole moment in an anion by disturbing its electron cloud. Because polarizing power follows the same trend as ionization energy: it increases across the period and decreases down the group. This is because small, highly charged cations have the highest polarizing power.