Silver nitrate is a good example of an ionic compound; a chemical formed from the mutual attraction of oppositely charged atomic groups. Silver nitrate is not only ionic, it is also highly soluble in water. Like all ionic compounds, when silver nitrate is dissolved in water, its molecules break apart into its constituent charged portions.
In the language of chemistry, an ion is an atom or group of atoms that carries a charge as the result of losing or gaining electrons. This charge can be either positive or negative. In an ionic compound, such as silver nitrate, one atom — silver — gives up an electron to a group of atoms — nitrate. This results in both the atom and the group becoming ions with opposite charges. The opposite charges cause the atom and the group to stick together, forming an ionic chemical compound.
One ion that is produced from dissolved silver nitrate is the silver ion "Ag+." This ion consists of a single atom of the element silver that has lost an electron and thus has a single positive charge. Positively charged ions such as this are known as "cations" in chemistry. Silver ions have some useful properties in medicine and are known to be toxic to a variety of microbes. A study by the National Public Health Institute of Finland found that silver ions controlled the growth of legionellae bacteria.
The counterpart ion to Ag+ which is formed when silver nitrate dissolves is the nitrate ion. This ion has the formula "NO3-." It has a single negative charge and since it is negative is called an "anion." It is a group of atoms, rather than a single atom, and is composed of a central nitrogen bonded to three oxygen atoms. The nitrate ion is found naturally in some foods such as spinach. It is also found in fertilizers and some other products. Nitrate can cause health concerns if you consume it in sufficient quantities.
Technically, silver and nitrate will not be the only ions present in the water. Of course, if the water is impure, there may be other ions present, such as sodium and chloride in salt water. Even if the water is completely pure, however, there will be additional ions. This is because, in pure water, a very small percentage of the water molecules spontaneously break apart into hydrogen ions (H+) and hydroxide ions (OH-). The H+ formed then combines with other water molecules to form hydronium ions (H3O+).