Polarizing Power Practice Problem

[Faaizah Arshad 1H]

Hi, I came across this question while practicing and am not sure how to approach it or what would be the correct answer.

What is the order of the following cations from least to most polarizing power?
Cs+ , Ba2+, Li+, Ca2+

Thank you!

[Aaina 2D]

Hi! Polarizing power is an atom's ability to pull electrons (distort e- in other atoms), so cations are the ones that tend to have high polarizing power because their positive charge attracts negative electrons. There are two factors to remember when it comes to polarizing power: charge and size. The cation with the most polarizing power should have the highest charge and the smallest size, so it can attract electrons more effectively (smaller size = nucleus has bigger pull on the e-).

In this case, the least would be Cs+ because in the periodic table, it has a small charge of +1 and is in period 6 = bigger size. Ba2+ would be next, because it's relatively the same size as Cs+, but has a higher charge and therefore has more polarizing power. Between Li+ and Ca2+, I believe Li+ would have the most polarizing power due to its smaller size even though Ca2+ has a bigger charge.

Therefore, your answer would be Cs+, Ba2+, Ca2+, Li+

Hope this helps, and please let me know what the right answer is!

[sophie esherick 3H]

Hey! For polarizing power, you have to think of the ionic radius and the charge of the ions. Polarizability is an atom's ability to distort electron clouds by pulling the electrons. This is done by cations because of their smaller size and overall positive charge. As you know ionic radius follows the same periodic trend as atomic radius, so it increases down a group and decreases across a periods for cations.

In your example, the least would be Cs+ because it is the largest (in Period 6), followed by Ba2+ since Ba2+ has a smaller ionic radius and a higher charge. The third would be Ca2+ since it is smaller than the previous two (Period 4) and has a 2+ charge to attract the electrons. Finally, that would leave lithium as the atom with the most polarizing ability due to it's much smaller size/ ionic radius (Period 2).

[clairehathaway 2J]

Hi! Polarizing power is an atom's ability to pull electrons (distort e- in other atoms), so cations are the ones that tend to have high polarizing power because their positive charge attracts negative electrons. There are two factors to remember when it comes to polarizing power: charge and size. The cation with the most polarizing power should have the highest charge and the smallest size, so it can attract electrons more effectively (smaller size = nucleus has bigger pull on the e-).

In this case, the least would be Cs+ because in the periodic table, it has a small charge of +1 and is in period 6 = bigger size. Ba2+ would be next, because it's relatively the same size as Cs+, but has a higher charge and therefore has more polarizing power. Between Li+ and Ca2+, I believe Li+ would have the most polarizing power due to its smaller size even though Ca2+ has a bigger charge.

Therefore, your answer would be Cs+, Ba2+, Ca2+, Li+

Hope this helps, and please let me know what the right answer is!

I agree with your answer, it's also what I got, but one of the UA worksheets has the correct answer listed as Ba2+, Cs+, Ca2+, Li+. Is this just an accident, because I also understood that Ba2+ has a higher charge meaning it would have more polarizing power.