Practice with ions

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Practice with "Predicting" Charges on Cations
To give you some practice determining the charges of cations, work on these examples.
Metal | Singlevalent-ion orMultiplevalent-ion | IonFormula(s) |
Na |   |   |
Ba |   |   |
Fe |   |   |
Mg |   |   |
Al |   |   |
Cu |   |   |
Ag |   |   |
 
Answers
 
Metal | Singlevalent-ion orMultivalent-ion | IonFormula(s) |
Na | S | Na+ |Ba | S | Ba2+ |
Fe | M | Fe2+Fe3+ |
Mg | S | Mg2+ |
Al | S | Al3+ |
Cu | M | Cu+Cu2+ |
Ag | S | Ag+ |
 

Practice with Charges of Anions
Take time now to get some practice with anions by working on the following exercise.
Non-metal | AnionFormula |
N |   |
O |   |
S |   |
Cl |   |
Br |   |
 
Answers
 
Non-metal | AnionFormula |
N | N3- |
O | O2- |
S | S2- |Cl | Cl- |
Br | Br- |
 

Polyatomic Ions
It is also possible for several non-metal atoms to cluster together in groups and form ions. They are called polyatomic ions. The formulas and charges of these polyatomic ions are not nearly so predictable as the simple anions you just studied. Nor are they all anions. The most used ones are listed in the table below.
Start by memorizing the namesand formulas (including charges) for these eight polyatomic ions. 
Important Polyatomic Ions |
Name | Formula |
acetate | C2H3O2- |
carbonate | CO32- |
nitrate | NO3- |
phosphate | PO43- |
sulfate | SO42- |
chlorate | ClO3- |
hydroxide | OH- |
ammonium | NH4+ |

Note that nearly all have "-ate" endings.  Note that nearly all contain oxygen with one other element, and nearlyall have negative charges.

Determining Formulas of Ionic Compounds
It is possible to figure out the formula of ionic compounds just by knowing the ions that form the compound. Ionic compounds may include only monatomic ions, only polyatomic ions or a mixture of both. The overall charge of the compound is zero. Thus, when the charges of the ions forming the compound are not equal, subscriptsneed to be used in order to indicate the appropriate number of ions needed to balance the positive and negative charges. In case the cation or anion included in the compound is a polyatomic ion parenthesis are used to indicate that the subscript applies to the whole cluster. The name of any ionic compound is done in a very simple way:
name of ionic compound = | name of cation | + | name ofanion |

Examples of Ionic Compounds |
Name | cation | anion | formula |
sodium chloride | Na+ | Cl- | NaCl |
calcium oxide | Ca2+ | O2- | CaO |
calcium hydroxide | Ca2+ | OH- | Ca(OH)2 |
calcium carbonate | Ca2+ | CO32- | CaCO3 |
lead (II) oxide | Pb2+ | O2- | PbO |
sodium bicarbonate | Na+ | HCO3- | NaHCO3 |
sodium thiosulfate | Na+ | S2O32- | Na2S2O3 |
ammonium nitrate |NH4+ | NO3- | NH4NO3 |

Determine what is wrong with the following formulas.

Ca(SO4) | calcium sulfate |
(NH4)2(SO4) | ammonium sulfate |
Ca(Cl)2 | calcium chloride |
(Al)2(SO4)3 | aluminum sulfate |

Correction
CaSO4 | calcium sulfate |
(NH4)2SO4 | ammonium sulfate |
CaCl2 | calcium chloride |
Al2(SO4)3 | aluminum sulfate |

Polyatomic Ions Revisited
Let's touch uponpolyatomic ions again. They are chemicals in which atoms fill their octet with electrons by using both covalent and ionic bonding. A simple example of this is the polyatomic ion, hydroxide.
Oxygen can fill up its "octet" using three different options. The ionic option (left side) involves the atom gaining two electrons to become an ion with a -2 charge. The covalent option (right side) involvesthe atom sharing two electrons from other atoms (hydrogen in this case). The polyatomic ion option (middle) requires the oxygen atom to obtain one electron by sharing with another atom (hydrogen in this case) and gain the other electron by taking it away from some willing electron-losing atom. In hydroxide ions, the shared electrons create a covalent bond which holds the oxygen and hydrogen atoms...
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