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 poly atomic ions (ions with more than one atom).
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.
PROPERTIES:
All ionic compounds form crystals.
Ionic compounds tend to have high melting and boiling points.
Ionic compounds are very hard and very brittle.
Ionic compounds conduct electricity when they dissolve in water.
FORMULAS:
Naming ionic compounds if you're given the formula
Example: Fe2(SO4)3
Step One: Name the cation and anion
The cation is always the first thing you see in the name, and the anion is always the second thing. In this case, you should recognize that Fe is "iron", and that SO4 is the "sulfate" ion. Generally, if one of these ions has more than one atom in it, you'll need to look it up in a chart.
Step Two: Figure out if you need a Roman numeral in the name.
If the cation in the compound you're naming is not a transition metal, then you definitely don't need to use a Roman numeral and the naming is done. If there is, then you need to figure out whether or not the cation can exist in more than one charge. If not, then you don't need a Roman numeral. If so, then move on to Step Three...
Step Three: Figure out what the Roman numeral should be
Basically, this should be fairly easy. A good rule of thumb is that usually the number of anions you have in the molecule is equal to the charge on the cation, and that the number of cations you have is equal to the number of anions. Using our example, there are three sulfate ions, meaning that iron has a charge of +3. Likewise, since there are two iron atoms, the sulfate has a charge of -2. Since iron has a charge of +3 in this compound, the name in this example is iron (III) sulfate.
Giving the formula of an ionic compound if you're given the name
Example: copper (II) fluoride
Step One: Translate the name into the ions
In copper (II) fluoride, the cation is the copper (II) ion and the anion is the fluoride ion. Hopefully, you realize that the copper (II) ion is simply Cu2+ and the fluoride ion is F-. If not, then you need to go back and review the rules for naming ions above.
Step Two: Put brackets around the ions, but leave the charges on the outside.
In this case, the copper (II) ion would be [Cu]2+ and the fluoride ion would be [F]-1. Never change anything in these brackets, ever!
Step Three: Put the ions next to each other.
When we do this here, we get [Cu]2+[F]-1
Step Four: Cross the charges:
The charge on the cation will be equal to the number of anions you have, and the charge on the anion will be equal to the number of cations you have. In our example, you should realize that we have one copper atom (because the charge on fluorine is -1) and two fluoride ions (because the charge on copper is +2). This gives us a formula of: [Cu][F]2
Step Five: Take the brackets away. The final formula for copper (II) fluoride is then CuF2
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 poly atomic ions (ions with more than one atom).
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.
PROPERTIES:
All ionic compounds form crystals.
Ionic compounds tend to have high melting and boiling points.
Ionic compounds are very hard and very brittle.
Ionic compounds conduct electricity when they dissolve in water.
FORMULAS:
Naming ionic compounds if you're given the formula
Example: Fe2(SO4)3
Step One: Name the cation and anion
The cation is always the first thing you see in the name, and the anion is always the second thing. In this case, you should recognize that Fe is "iron", and that SO4 is the "sulfate" ion. Generally, if one of these ions has more than one atom in it, you'll need to look it up in a chart.
Step Two: Figure out if you need a Roman numeral in the name.
If the cation in the compound you're naming is not a transition metal, then you definitely don't need to use a Roman numeral and the naming is done. If there is, then you need to figure out whether or not the cation can exist in more than one charge. If not, then you don't need a Roman numeral. If so, then move on to Step Three...
Step Three: Figure out what the Roman numeral should be
Basically, this should be fairly easy. A good rule of thumb is that usually the number of anions you have in the molecule is equal to the charge on the cation, and that the number of cations you have is equal to the number of anions. Using our example, there are three sulfate ions, meaning that iron has a charge of +3. Likewise, since there are two iron atoms, the sulfate has a charge of -2. Since iron has a charge of +3 in this compound, the name in this example is iron (III) sulfate.
Giving the formula of an ionic compound if you're given the name
Example: copper (II) fluoride
Step One: Translate the name into the ions
In copper (II) fluoride, the cation is the copper (II) ion and the anion is the fluoride ion. Hopefully, you realize that the copper (II) ion is simply Cu2+ and the fluoride ion is F-. If not, then you need to go back and review the rules for naming ions above.
Step Two: Put brackets around the ions, but leave the charges on the outside.
In this case, the copper (II) ion would be [Cu]2+ and the fluoride ion would be [F]-1. Never change anything in these brackets, ever!
Step Three: Put the ions next to each other.
When we do this here, we get [Cu]2+[F]-1
Step Four: Cross the charges:
The charge on the cation will be equal to the number of anions you have, and the charge on the anion will be equal to the number of cations you have. In our example, you should realize that we have one copper atom (because the charge on fluorine is -1) and two fluoride ions (because the charge on copper is +2). This gives us a formula of: [Cu][F]2
Step Five: Take the brackets away. The final formula for copper (II) fluoride is then CuF2