adding "ate"

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tchar96_1F
Posts: 14
Joined: Fri Sep 26, 2014 2:02 pm

adding "ate"

Postby tchar96_1F » Sun Nov 23, 2014 4:10 pm

Hi,

I thought you only add "ate" when the compound is a negative charge. So my first question is - why do some compounds have "ate" at the end, but no overall negative charge?

And example is number 16.29 in the book, part a:
It wants you to write the chemical formula for "potassium hexacyanidochromate(III)"
The answer is K3[Cr(CN)6)]. Why is there no overall negative charge?

Thanks!

Juliana Smith 2G
Posts: 14
Joined: Fri Sep 26, 2014 2:02 pm

Re: adding "ate"

Postby Juliana Smith 2G » Sun Nov 23, 2014 4:50 pm

In this case, I believe that [Cr(CN)6] would've had an overall -3 charge, but because of the K3, the compound is neutralized. However, the compound itself is an ion: [Cr(CN)6]3- to which K+ ions binded. Therefore the compound ion is not overall neutral, if thats makes sense, because you needed the K+ ions, but its not neutral by itself. The K+ ions wouldn't need to bind there if the compound was already neutral which is why they put "chromate" instead of "chronium III".

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

Re: adding "ate"

Postby GinaYoung1L » Sun Nov 23, 2014 6:36 pm

As mentioned in the textbook, there is a small distinction between the terms complex and coordination compound. The complex itself (the metal and ligands) can have a charge (and be called anionic or cationic.) Therefore, the complex anion or anionic complex needs an -ate attached to the metal's stem name. If the complex has a charge, it will interact with cations or anions outside (such as K+) to form an electrically neutral coordination compound. So, you have to look at the charge of the bracketed complex to determine if it needs the -ate attachment instead of looking at the electrically neutral coordination compound.

In this problem, the K3[Cr(CN)6)] is a neutral coordination compound as expected, but its complex [Cr(CN)6)] is not. The complex is what determines your addition of the ending -ate.


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