Clarifying Naming ligands in Formula

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michelleguan3a
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Joined: Fri Sep 26, 2014 2:02 pm

Clarifying Naming ligands in Formula

Postby michelleguan3a » Sat Dec 13, 2014 1:54 pm

I am confused about what is the correct way of naming the ligands in the formula. On chemistry community, I have seen people say to list the anionic ligand first and then the neutral ligand and to list them in alphabetical order. I have seen that the textbook says to list the ligands in alphabetical order but on multiple online sites it says to list the neutral ligand first and then the anionic one. Which method is the correct one??

GinaYoung1L
Posts: 16
Joined: Fri Sep 26, 2014 2:02 pm

Re: Clarifying Naming ligands in Formula

Postby GinaYoung1L » Sat Dec 13, 2014 2:10 pm

I think you are confused about the difference between ligands, ions, complexes, and coordination compounds.

Regarding the chemical formula of the coordination compound:

1. The complex consists of the ligands and the metal ion inside the brackets. In here, the ligands are listed based on the alphabetical order of the chemical symbols.

2. The coordination compound (the complex and any outside ions such as Cl-, K+, etc) goes by: cation before anion. So, if the complex is positively charged (cation), it goes before the negative ion (anion.) If the complex is negatively charged (anion), it goes after the positive ion (cation.)
Ex: Na+ before [metal and ligands]-
Ex: [metal and ligands]+ before Cl-

*However, note that the coordination compound is always electrically neutral. Thus, the charges of the cations and anions will balance each other.
Ex: [Ag(NH3)2]+ and Cl- have charges when they are separate. But, [Ag(NH3)2]Cl is neutral.

michelleguan3a
Posts: 14
Joined: Fri Sep 26, 2014 2:02 pm

Re: Clarifying Naming ligands in Formula

Postby michelleguan3a » Sat Dec 13, 2014 2:20 pm

Thank you for your response!
What I was actually referring to was the ligands inside of the ion complex. For example, in the practice final 2013, question Q5B (pg 256), the answer for the formula of tetraamminedichloroplatimum(IV) is [Pt(NH3)4Cl2]. According to this method, the neutral ligand (NH3) is listed before the anionic ligand (Cl2). However, if we were to follow the textbook's method of listing the ligands in alphabetical order, the answer should be [Pt(Cl)2(NH3)4]. Will both answers be accepted on the test?
Last edited by michelleguan3a on Sat Dec 13, 2014 2:59 pm, edited 1 time in total.

GinaYoung1L
Posts: 16
Joined: Fri Sep 26, 2014 2:02 pm

Re: Clarifying Naming ligands in Formula

Postby GinaYoung1L » Sat Dec 13, 2014 2:24 pm

I'm not sure what it means to list ligands by their electrical charges. However, I have never encountered any problems on exams (both real and practice) by listing them in alphabetical order.

GinaYoung1L
Posts: 16
Joined: Fri Sep 26, 2014 2:02 pm

Re: Clarifying Naming ligands in Formula

Postby GinaYoung1L » Sat Dec 13, 2014 2:26 pm

Strangely, my course reader is missing that page with number 5 on it. Sorry...


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