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When are complex ions formed?


jlai928

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Hi all,

I think I'm seriously missing a huge chunk of knowledge about complex ion formation. I know what they are but for example, when SiCl4 is added to water the equation is SiCl4 + 4H2O(l) --> Si(OH)4(s) + 4HCl(aq). I'm confused about the Si(OH)4. When do you know a complex ion will be formed??

What I put down for that was SiCl4 + 2H2O --> SiO2 + 4HCl, which is completely wrong..

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Complex ions are formed when metal ions are added to water, I believe! (Or any other ligand, such as ammonia.) Since Si is a metal, as you can see from the periodic table, we can see that it'll form a complex ion. If you're unsure of which elements are metals (I was, oops!) a quick google search will find some good pictures. ;)

Actually, Si is a bit funny because a lot of the stuff I found says it's a metalloid, rather than a metal - but I guess that must be enough for complex ion formation?

Hope this helps a bit! :)

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Yes! Complexes are formed when a metal reacts with ligands as Melissi is pointing out. However, not any metal will form complexes. Only the ones with high charge density (high oxidation states). For example, Na and Mg will not form complexes as their charge as ions (1+ and 2+ respectively) is not enough to attract the lone pair of the ligand. Aluminium on the other hand which has a charge of 3+ when it is an ion will attract the ligands. The most notable metals which forms complexes are the d-block elements in the periodic table as these have multiple and high oxidation numbers.

Edited by Kaushalz
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Yes! Complexes are formed when a metal reacts with ligands as Melissi is pointing out. However, not any metal will form complexes. Only the ones with high charge density such (high oxidation states). For example, Na and Mg will not form complexeses as their charge as ions (1+ and 2+ respectively) is not enough to attract the lone pair of the ligand. Aluminium on the other hand which has a charge of 3+ when it is an ion will attract the ligands. The most notable metals which forms complexes are the d-block elements in the periodic table as these have multiple and high oxidation numbers.

Thanks for elaborating on what Melissi said. I understand now. Just had to clear it up. Ugghh chemistry..

Complex ions are formed when metal ions are added to water, I believe! (Or any other ligand, such as ammonia.) Since Si is a metal, as you can see from the periodic table, we can see that it'll form a complex ion. If you're unsure of which elements are metals (I was, oops!) a quick google search will find some good pictures. ;)

Actually, Si is a bit funny because a lot of the stuff I found says it's a metalloid, rather than a metal - but I guess that must be enough for complex ion formation?

Hope this helps a bit! :)

Simple and straightforward thanks!

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