Important things to know about ionic compounds
What are ionic compounds?
Ionic compounds are basically defined as being compounds where two or more ions are held next to each other by electrical attraction. One of the ions has a positive charge (called a "cation") and the other has a negative charge ("anion"). Cations are usually metal atoms and anions are either nonmetals or polyatomic ions (ions with more than one atom). Think back to grade school: The same thing that makes the positive and negative ends of a magnet stick to each other is what makes cations and anions stick to each other.
Usually, when we have ionic compounds, they form large crystals that you can see with the naked eye. Table salt is one example of this - if you look at a crystal of salt, chances are you'll be able to see that it looks like a little cube. This is because salt likes to stack in little cube-shaped blocks.
Sometimes when you see a salt, it looks like a powder instead of a cube. This doesn't mean that the salt is not a crystal - it means that the crystals are just so small that you can't see them with the naked eye. If you were to put the powder under a microscope, chances are that you would see little geometric blocks.
So, what are the main properties of salts? Well, I'm sure glad you asked...
If you put a hairdryer in the bathtub with you under ANY conditions, you will fry yourself!
How do we name ionic compounds?
For practice problems with complete
solutions, click here.
The best way to go about naming ionic compounds is to take a look at the formula and figure out the names of the cation and anion. When you've got that, just stick them together and you've got the name of the compound.
So, how do we name cations? If the cation is a main block element, the name of the cation will just be the name of the element. So, the Na+ ion is the "sodium" ion. Not too challenging. However, if the cation is a transition metal, what you need to do is to check out whether or not there is more than one possible charge for that element. For example, iron can have a charge of either +2 or +3. As a result, you need to specify whether the cation has a +2 or a +3 charge. When you've done this, just put the number after the name of the element in Roman numerals. For example, the Fe+3 ion just has the name "iron (III)".
How about anions? If the anion has only
one atom in it, then the name of the anion is the same as the name of the
element EXCEPT the end of the element name is taken off and "-ide"
is added to the end. Thus, oxygen becomes "oxide", sulfur becomes
"sulfide", phosphorus is "phosphide", et cetera. If the
anion has more than one atom, then we'd say that it's a "polyatomic ion",
meaning (not surprisingly) that the anion has more than one atom. Look up the
polyatomic ion in a table (or pull it out of your... uh... memory), and
you've got the name. Thus,
Handy methods for naming compounds
Naming ionic compounds if you're given the formula
Let's go through this using an example: Fe2(SO4)3
Step One: Name the cation and anion
Step Two: Figure out if you need a
Roman numeral in the name.
Step Three: Figure out what the Roman
numeral should be
Step Four: Check your work
But... what if we find a mistake when
we check our work?
When this happens, look at the anion. In
our example of
Giving the formula of an ionic compound if you're given the name
We'll use an example to find the formula of an ionic compound: copper (II) fluoride
Step One: Translate the name into the
Step Two: Put brackets around the ions,
but leave the charges on the outside.
Step Three: Put the ions next to each
Step Four: Cross the charges:
Step Five: Take the brackets away. The final formula for copper (II) fluoride is then
IF the charges on the ions can be divided by the same number, then do it before you do step four. For example, if you were to find the formula for manganese (IV) oxide, you'd realize in step three that both manganese (IV) and oxygen have charges that can be divided by two. Instead of crossing the +4 for manganese and the -2 for oxygen, you'd simplify it so that you cross a +2 for manganese and a -1 for oxygen.
IF we have a polyatomic ion, such as sulfate or ammonium, you need to replace the brackets with parentheses in step five. For example, if you end up with [NH4]2O as the formula for ammonium oxide at the end of step four, you'd simply replace the brackets with parentheses in step five to give you (NH4)2
Other stuff I might have forgotten above
In no particular order, here's some other stuff about ionic compounds that you might have wondered about:
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