Trends of Polarizing Power

[Rachel Brown 3A]

Can someone explain to me what makes an element or ion more or less polarizing? Is there a periodic trend to follow or something polarizing power is proportionally related to?

[Julia Meno 1D]

To understand polarizing power, it might be helpful to first understand when an atom is highly polarizable.

Atoms or ions are highly polarizable when their electron clouds can undergo a large distortion (they exert weak control over their outermost electrons). Therefore, large anions are highly polarizable because their outermost electrons are further away from the nucleus and they have a negative charge, so these atoms can afford to lose their electrons.

Atoms/ions with polarizing power are the ones that cause the large distortions in highly polarizable atoms/ions. This is why small cations have high polarizing power because they want electrons and can hold on to them better because of their size.

So when you're looking at the periodic table and trying to decide what atom is more polarizable or has more polarizing power, you will definitely have to take into account atomic/ionic radius and charge.

I hope this makes sense!

[Ashin_Jose_1H]

Atoms and ions are considered polarizable if they readily undergo a large distortion with their electron clouds. An anion is said to be highly polarizable if it is large. In the large anion, the nucleus exerts a weak force on the electrons in the outermost shell. So, the electron cloud can become easily distorted.

Atoms and ions causing the large distortions are said to have high polarizing power. A small and highly charged cation is said to have high polarizing power. Because the radius is small, the nucleus has a stronger pull on the anion's electrons, thus causing the distortion.

As cations, become smaller and more highly charged, their polarizing power increases. So, the polarizing power increases from left to right across a period. For example, Beryllium²⁺ has a higher polarizing power than Lithium¹⁺. However as we go down a group, the cations become larger, therefore decreases in polarizing power. For example, Magnesium²⁺ has a lower polarizing power than Beryllium²⁺.

[Mei Blundell_1J]

Is it true that cations and anions have opposite polarizability trends?

[Alexis Bravo 1D]

Yes cations and anions show opposite polarizability trends because cations are smaller than their parent atoms and less polarizable and anions show the opposite trend.