## Question 1F.3

Suraj Doshi 2G
Posts: 100
Joined: Fri Aug 02, 2019 12:15 am

### Question 1F.3

The question is:

Place the following ions in order of increasing ionic radius: S^2-, Cl-, P^3-.

Why do they not all have the same ionic radius if they have the same number of electrons?

KTran 1I
Posts: 52
Joined: Fri Aug 30, 2019 12:15 am

### Re: Question 1F.3

The order would be P^3- > S^2- > Cl-

Across a period, atomic radius decreases because the positive charge of the nucleus increases, therefore increasing the pull on the electrons. Since electrons are added, the net positive pull on all the electrons decreases (the positive charge has to spread out over a disproportional amount of negative charge), which means the radius increases. Even though all three have the same number of electrons, the one with the least number of protons (lowest atomic number: P^3-) would have the largest radius since its nucleus pulls less on the electrons, followed by S^2-, and Cl-, which has the greatest atomic number, and consequently the greatest positive charge in its nucleus, of the three ions.

Osvaldo SanchezF -1H
Posts: 122
Joined: Wed Sep 18, 2019 12:21 am

### Re: Question 1F.3

It doesn't matter if the ions have the same number of electrons because what matters is the total pull the nucleus has on the electrons which affects the radii. So the best way to determine how strong the attraction of electrons to the nucleus is, look at the protons present in the elements which cause the pull of the electrons to the nucleus. More protons means a stronger pull and a decrease in radii and the opposite is true as well.

LReedy_3I
Posts: 51
Joined: Fri Aug 30, 2019 12:17 am

### Re: Question 1F.3

Although they have the same number of electrons, the charge is different, and the interaction with the nucleus is different because some will have more protons and hold the electrons tighter.

Melvin Reputana 1L
Posts: 55
Joined: Sat Aug 17, 2019 12:16 am

### Re: Question 1F.3

Yes, they have the same number of electrons; however, each ion's atomic number is different. This causes varying effective nuclear charges within each ion. For example, for the chlorine ion, the nuclear charge is greater compared to the phosphorus ion and sulfur ion. Despite having the same number of electrons, the nucleus of the chlorine ion has a greater pull on the electrons, thus making its atomic radius smaller compared to the other ions.

melinak1
Posts: 25
Joined: Tue Sep 24, 2019 12:17 am

### Re: Question 1F.3

Melvin Reputana 1L wrote:Yes, they have the same number of electrons; however, each ion's atomic number is different. This causes varying effective nuclear charges within each ion. For example, for the chlorine ion, the nuclear charge is greater compared to the phosphorus ion and sulfur ion. Despite having the same number of electrons, the nucleus of the chlorine ion has a greater pull on the electrons, thus making its atomic radius smaller compared to the other ions.

this is a clear explanation, thanks!