We just talked about naming binary covalent compounds. Now we’re going to step aside and talk about ionic compounds. Let’s review what an Ionic Compound is. Chemical Compound
Ionic Compound –
Consists of Cations (positively charged) and Anions (negatively charged).
They are generally Nonmetal bonded to a Metal.
This means we are talking about naming a nonmetal bonded to a metal. This also means we have a positive and negative charged ion.
|Problem: Which of the following is a Cation & which of the following is an Anion? Li+, F–, O2–, Mg2+|
Plan: We look at the above definition and see that a Cation is positively charged, and the Anions are negatively charged. From this, we know which are Cations and which are Anions.
Li+ – Cation
F– – Anion
O2– – Anion
Mg2+ – Cation
Discussion: Look at your periodic table for a second. Where do most of the cations and anions seem to be? On the left side of the periodic table (group 1A and 2A), you will find your positively charged cations and on the far right (group 6A and 7A) you will find your anions. We’ll talk about why this is in a later chapter, but it’s worth noting now.
Now that we know the difference between a Cation and Anion we can get somewhere. We don’t use Greek prefixes when naming Ionic compounds. Instead, we know the charge of one cation and the charge of the anion and we know what the subscript on each of the compounds are.
For example, if I have a Na+ cation and a Cl- anion (know that Na has a +1 charge since it’s found in group 1A, and I know that Cl has a -1 charge since it’s found in group 7A), so a -1 and a +1 = 0.
Therefore, we have 0 subscripts and it’s just listed as NaCl, which is our common table salt.
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What if I have a cation ofMg+2and an anion of F-1? They don’t just cancel out as they did on NaCl. Since I have 2 Mg’s for 1 F, what I need to do is double the F’s. This leaves us with MgF2. The next step is, how do we name it?
Ionic Compound: Magnesium Fluoride
When naming an Ionic Compound, the first term always gets named its elemental name. Therefore in MgF2, the first part of the name we know will be Magnesium.
Now for the second part, all we need to do is take its elemental name (Fluorine), remove the last suffix which in this case is “ine” and add an “ide”. We’ve now got the ionic compound’s name. Magnesium Fluoride. This is the simplest case of naming an ionic compound. There are some other problems that can arise.
What if we have a metal that forms more than one monoatomic ion? This means an ion that can form more than one charge. The person writing the formula must list the charge in roman numerals.
Therefore, the person naming it can realize what charge is being talked about. Below is a list of some metals that can form more than one charge.
|Chromium||Cr2+ and Cr3+|
|Cobalt||Co2+ and Co3+|
|Copper||Cu+ and Cu2+|
|Iron||Fe2+ and Fe3+|
|Lead||Pb2+ and Pb4+|
|Mercury||Hg2+ and Hg2+|
|Tin||Sn2+ and Sn4+|
Therefore, if one of these metals is being named in an ionic compound. The person writing the formula MUST give the charge in parentheses in Roman numerals next to the cation. Chemical Compound
You’ll notice that all the ions listed above are found in the transitional metals on the periodic table. Let’s try naming a binary ionic compound.
|Problem: Give the ionic systematic name of K2O|
Plan: We will name this following the above naming rules.
Discussion: No greek prefixes were needed because Potassium is not a monoatomic ion.
Naming nonbinary ionic compounds.
There are more nonbinary ionic compounds than there are binary, thus it is important to be able to recognize polyatomic ions. Polyatomic ions act just like Na+ or Cl–, except they have more than one element making up the overall cation or anion.
For example, SO42- has the same charge as O2-, but how would we name SO42-? One answer, we must memorize them!
The ones listed above are the most common polyatomic ions. A couple of things you might notice is that the polyatomic ions above are all negatively charged.
It’s a good observation but that is not always the case. For example, Ammonium is NH4+. Therefore, you can have both polyatomic cations and anions.
Okay, so we’ve got this huge list of polyatomic ions. How do we name these? Well to answer that, we just follow the same rules as above, we cross the charges and name them.
Let’s try an example below and see if you follow.
|Problem: What is the systematic name for Na2SO4|
Plan: We’ll use the general rules talked about at the beginning of this section to name this. We’ll look at the list of polyatomic ions above to name the anion.
Discussion: Remember not to do anything fancy with the Na2. Just name it sodium since it’s ionic. Also, don’t do anything fancy with the SO4, just name it to sulfate. Because the sulfate has a 2- charge, and because sodium has a +1, we need two sodium’s for each sulfate to account for a zero charge overall. Chemical Compound
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