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Combining Ions, Advanced

Ionic compounds can be made of one kind of metal and one kind of non-metal. Metals make positively charged ions by losing electrons. Non-metals make negatively charged ions by gaining electrons. Positive ions must combine with negative ions in order to make a neutral compound.

For example, a positive ion with a +1 charge (A+) combines with a negative ion with a –1 charge (B–) like this:

one A+ and one B– make the combination AB

The combination is written all together without showing the charges. The number of ions in the combination is selected so that the total charge for all ions in the combination is zero. Here is another example:

A positive ion with a +2 charge (A2+) combines with a negative ion with a –1 charge (B–) like this:

one A2+ and two B– make the combination AB2

Here the combination has a two after the negative ion because it takes two of them to balance one of the positive ions. You can think of this combination like this:

A2+ plus B– plus B–

If you put all three ions in a box, then the total charge for everything in the box is zero:

A2+
B–       B–

Here is another example, a positive ion with a +2 charge (A2+) combines with a negative ion with a –3 charge (B3–) like this:

three A2+ and two B3– make the combination A3B2

Here the combination has a three after the positive ion and a two after the negative ion because it takes three A2+ ions to balance two B3– ions. You can think of this combination like this:

A2+ plus A2+ plus A2+ plus B3– plus B3–

If you put all five ions in a box, then the total charge for everything in the box is zero:

A2+   A2+   A2+
B3–       B3–

In summary, ions must be combined so that the total positive and the total negative charge is equal. This requires that there are enough of each ion to make the total positive and the total negative charge equal to the least common multiple of the two charges. This is summarized in the following table:

  B– B2– B3– B4–
A+ AB A2B A3B  
A2+ AB2 AB A3B2  
A3+ AB3 A2B3 AB  
A4+        

So far these examples have used the symbols A and B to stand for any element. Most real ions will be plus or minus 1, 2, or 3. When building chemical formulas using real ions the example formulas in the table above give all of the possible combinations for all the ions with those charges. Fill in the blank places in the table for ions with a plus or minus four charge. First try it yourself, then check with classmates to make sure you have the right idea and get the correct responses in your table.

Naming ionic compounds of two elements is very simple. Just name the metal then give the name of the non-metal while changing the end of the name to –ide. Do not use prefixes! The name of NO2 is nitrogen dioxide. The name of the ionic compound CaCl2 is just calcium chloride. Since calcium is always a +2 ion and chloride is a –1 ion this is the only possible combination of these ions. Here are a few more example names:



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Monatomic Ions
Group 1 Group 2   Group 13 Group 14 Group 15 Group 16 Group 17
Li+ Be2+ B3+ — N3– O2– F–
Na+ Mg2+ Al3+ Si4+ P3– S2– Cl–
K+ Ca2+ Ga3+ Ge4+ As3– Se2– Br–
Rb+ Sr2+ In3+ Sn2+ / Sn4+ Sb3– Te2– I–
Cs+ Ba2+ Tl1+ / Tl3+  Pb2+ / Pb4+ Bi3+ / Bi5+ — —

Add to this table the hydrogen ion (H+), which is the ion found in acids. Compounds formed from H+ and some anion are acids and require a separate naming convention from ionic compounds. Consult your notes and the textbook on how to name acids.

Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9 Group 10 Group 11 Group 12
 Sc 
3+ 		 Ti 
4+ / 3+ 		 V 
5+ / 4+ / 3+ / 2+ 		 Cr 
6+ / 3+ / 2+ 		 Mn 
4+ / 2+ / 3+ 		 Fe 
2+ / 3+ 		 Co 
2+ / 3+ 		 Ni 
2+ / 3+ 		 Cu 
2+ / 1+ 		 Zn 
2+
 Y 
3+ 		 Zr 
4+ 		             Ag 
1+ 		 Cd 
2+
 La 
3+ 		 Hf 
4+ 		             Au 
3+ / 1+ 		 Hg2+ / Hg22+ 

Here is a table of the transition metal ions. Do not memorize charges but be able to figure out the charges from the names or formulas of compounds.

The tables below show the names of some polyatomic ions. The ones you should memorize are in bold. Add just one positively charged polyatomic ion: ammonium ion (NH4+).

1– Anions
Chlorate ClO3–
Chlorite ClO2–
Cyanide CN–
Dihydrogen Phosphate H2PO4–
Hydride H–
Hydrogen Carbonate HCO3–
Hydrogen sulfate HSO4–
Hydroxide OH–
Hypochlorite ClO–
Nitrate NO3–
Nitrite NO2–
Perchlorate ClO4–
Permanganate MnO4–
Thiocyanate SCN–
2– Anions
Carbonate CO32–
Chromate CrO42–
Dichromate Cr2O72–
Hydrogen phosphate HPO42–
Selenate SeO42–
Sulfate SO42–
Sulfite SO32–
Thiosulfate S2O32–
3– Anions
Arsenate AsO43–
Borate BO33–
Phosphate PO43–
Instructions

Work together in teams of three or four to create 42 combinations of ions. Start by making three combinations for each group (column) of cations using a different cation and anion for each of the three. Do not use any cation or anion more than once. Create a table in which to record the cation, anion, formula and name for each combination you create. Each group member must make his or her own copy of this table. Remember that combinations starting with the H+ ion are acids. Name them as appropriate! An example has been included below to get you started but create your table on your own paper. To earn credit for this assignment you must create and record 42 combinations.


Example Table
Positive Ion Negative Ion Formula for Combination Name
Li+ NO2– LiNO2 lithium nitrite
Na+ NO3– NaNO3 sodium nitrate
K+ N3– K3N potassium nitride
This homework belongs with the Chemical Nomenclature group activity.
Additional Naming Practice Problems
Homework I
Homework II
Homework III
Many problems were inspired by those at Mr. Basset’s Site.
ChemTeam Additional Naming Information and Practice
(has lots of exercises with answers) Last updated: Jan 22, 2020        Home