## Homework 2.59

Lauryn Shinno 2H
Posts: 59
Joined: Fri Sep 28, 2018 12:24 am

### Homework 2.59

The problem asks you to place the ions in order of increasing ionic radius: S^2-, Cl^-, P^3-. I understand that ionic radii decrease from left to right across a period, but I don't get what the exponents do. How do they affect the size of the radius?

Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

### Re: Homework 2.59

I think the exponents are just based on the trends on the periodic table. For group 15, their charges are -3 which explains P^-3. For group 16 and 17, it's -2 and -1 respectively. That explains S^-2 and Cl^-1.

Luc Lorain 1L
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

### Re: Homework 2.59

The presence of exponents signifies that the atoms provided are not in their ground state but rather in ionic form. If we reflect on what Dr. Lavelle said in his lecture on Wednesday, ionic radius should increase as we go down a group. This is because each additional shell shields some electrons from the nucleus's pull. Ionic radius should also decrease across a period (left to right), as the nuclear charge increases with atomic number while the number of shells remains static across a period.

It is also important to note (although perhaps not super relevant to this problem) that cations tend to be smaller than their parent atoms and anions tend to be larger than their parent ions.

Isabel Nakoud 4D
Posts: 101
Joined: Fri Sep 28, 2018 12:27 am

### Re: Homework 2.59

Luc Lorain 1L wrote:The presence of exponents signifies that the atoms provided are not in their ground state but rather in ionic form. If we reflect on what Dr. Lavelle said in his lecture on Wednesday, ionic radius should increase as we go down a group. This is because each additional shell shields some electrons from the nucleus's pull. Ionic radius should also decrease across a period (left to right), as the nuclear charge increases with atomic number while the number of shells remains static across a period.

It is also important to note (although perhaps not super relevant to this problem) that cations tend to be smaller than their parent atoms and anions tend to be larger than their parent ions.

Does an increase in effective nuclear charge = decrease in size of the ion?