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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: OTI on October 26, 2015, 10:15:22 PM

Title: Rules for making ionic compounds
Post by: OTI on October 26, 2015, 10:15:22 PM: So, my teacher made this card game called ionic gin where you have to place down ionic compounds. However, all we've learned in class so far is the naming system and not what's "possible". As far as I can see, you can just pile up ions and cancel all the charges. So what are the rules for making ionic compounds? For example, can I have a fluoride, a potassium, and a calcium in an ionic compound?

Thanks.
Title: Re: Rules for making ionic compounds
Post by: potassium_carbonate on October 26, 2015, 10:53:56 PM: Hi there. Ionic compounds are quite simple once you get the hang of them. An ionic compound can only form between a metal and a nonmetal, or a polyatomic ion. A polyatomic ion is a group of atoms covalently bonded that has a charge. Take, for example, the carbonate ion: [CO₃]^2-.

Metals always form a positive ion (cation) and nonmetals always form a negative ion (anion)

Some examples include:

[K]⁺ [Cl]^- :rarrow: KCl
[Ca]²⁺ [F]^- :rarrow: CaF₂

Here is an example with a polyatomic ion. It's also my username. :)
[K]⁺ [CO₃]² :rarrow: K₂(CO₃)

I hope this helps! Good Luck!
Title: Re: Rules for making ionic compounds
Post by: OTI on October 26, 2015, 11:22:14 PM: Thanks! That clears it up a bit. The only problem I have left is with the example I gave. How many different kinds of metals can I have in an ionic bond assuming that there is one non metal?
Title: Re: Rules for making ionic compounds
Post by: potassium_carbonate on October 26, 2015, 11:28:16 PM: An ion is usually made up of two main "formula units." These can be either an elemental ion, ie, [K]⁺ or a polyatomic ion. (Here is a list of common polyatomic ions--http://yeahchemistry.com/sites/default/files/Common%20Polyatomic%20Ions.PNG (http://yeahchemistry.com/sites/default/files/Common%20Polyatomic%20Ions.PNG))

Combinations include:

A metal and a nonmetal
A cation polyatomic ion and any type of anion
An anion polyatomic ion and any type of cation
A cation polyatomic ion and an anion polyatomic ion.

I hope this was clear.
Title: Re: Rules for making ionic compounds
Post by: OTI on October 26, 2015, 11:41:33 PM: Yeah. But can I have an ionic compound with a fluoride, a potassium, and a calcium?
Title: Re: Rules for making ionic compounds
Post by: potassium_carbonate on October 26, 2015, 11:46:11 PM: You can have potassium fluoride or calcium fluoride. I don't believe you can have both.
Title: Re: Rules for making ionic compounds
Post by: OTI on October 26, 2015, 11:47:54 PM: Okay, thanks. I think I get it now.
Appreciate it.
Title: Re: Rules for making ionic compounds
Post by: potassium_carbonate on October 26, 2015, 11:49:23 PM: :) Best of luck!
Title: Re: Rules for making ionic compounds
Post by: Borek on October 27, 2015, 03:28:55 AM: Quote from: OTI on October 26, 2015, 11:41:33 PM
Yeah. But can I have an ionic compound with a fluoride, a potassium, and a calcium?

I have not heard about this particular compound, but in general - yes, such things happen. They are quite rare, but there are at least three cases worth of remembering:

1. Ammonium iron(II) sulfate AKA Mohr's Salt (NH₄)₂Fe(SO₄)₂·6H₂O (rare case of a stable Fe(II) salt which doesn't get oxidized to Fe(III) when exposed to air).

2. Whole class of alums with a general formula XY(SO₄)₂·12H₂O, where X is a monovalent cation (like Na⁺, K⁺, NH₄⁺) and Y is a trivalent cation (like Al³⁺ or Cr³⁺).

3. Basic and acidic salts - like NaHCO₃ (in which technically H⁺ plays a role of a cation), or basic copper carbonate Cu₂(OH)₂CO₃.
Title: Re: Rules for making ionic compounds
Post by: potassium_carbonate on October 27, 2015, 08:01:24 AM: Thanks, Borek, I never knew that! :o
Title: Re: Rules for making ionic compounds
Post by: missmendeleev on October 27, 2015, 08:26:41 AM: Depending on whether two or more of the elements form a polyatomic ion together, it is possible.
Title: Re: Rules for making ionic compounds
Post by: Enthalpy on October 28, 2015, 11:05:14 AM: Minerals are full of examples. "Silicates of X and Y". In Earth's crust, silicates of one metal are rare and sought as useful ore.