Ionic compounds consist of cations(positively charged ions) and anions(negatively charged ions). The total charge of any ionic compound must be zero. A very familiar example of an ionic compound is common table salt, NaCl (sodium chloride). Na is a positively charged cation with a charge of +1, Cl is a negatively charged anion with a charge of -1. The formula for NaCl is such because the charge of Na(+1) plus the charge of Cl(-1) is zero.
If two ions are combined with different charges the correct number of each ion must be taken in order to make the total charge zero. For example when barium (Ba with a +2 charge) combines with fluoride (F with a charge of -1) two F ions are needed so that the total charge is zero. Therefore the correct formula for barium fluoride would be BaF2. If more than one of an ion containing more than one elements required, like ammonium (NH4), parenthesis must be used. For example the formula of ammonium carbonate which contains NH4 with a +1 charge and CO3 with a -2 charge the formula is (NH4)2CO3. Two ammonium ions are required to balance out the -2 charge of carbonate and parenthesis must be used since ammonium consists of more than one element. Monatomic ions (ions consisting of only one ion) do not require parenthesis when more than one ion is used.
When naming compounds simply take the name of the cation and follow it by the name of the anion. For example Al2(SO4)3 is called aluminum sulfate. Some ions can have more than one oxidation state(charge) like iron which can be iron(II) with a +2 charge or iron(III) with a + 3 charge. When naming compounds containing these ions determine which form is present by looking at the charge and number of the anion which accompanies the cation. FeCl3 would be iron(III) chloride since Cl is -1 and FeCl2 would be iron(II) chloride.
To practice naming and writing formulas for ionic compounds click below and a mini-program(you must have a browser that supports Java) will start which will ask random names and formulas. Click on Start to Start the program. Use the keyboard to enter your response and either click on OK or press the Enter key when the answer is as you want it. If you make any errors use the backspace key.
Download Symname for use on your computer:
Download sym10.zip(128,383 bytes)for Windows 3.0 and 3.1
Download Sym20.zip(133,971 bytes) for Windows 95 and NT