The polyatomic ion in this compound is the carbonate ion, CO2−3 C O 3 2 − . Since it has a 2- charge it is an anion, a negative ion. Putting the two names together produces the name of the ionic compound. Sodium + carbonate = sodium carbonate.

Other common compounds that contain polyatomic ions include sodium bicarbonate (NaHCO3), also known as baking soda; sodium nitrite (NaNO2), an inhibitor of bacterial growth in packaged meats; and calcium carbonate (CaCO3), the active ingredient in antacids such as TUMS®.

Explanation: Detergents and soaps, the salts of long chain fatty acids are probably the best examples. These are certainly polyatomic. Of course, in the kitchen we commonly use bicarbonate of soda, NaHCO3 , (and other salts) as a raising agent.

Some examples are: NO−3, this is nitrate ion and it is regarded as a polyatomic ion because there is one nitrogen and three oxygen atoms and it has a negative charge. SO2−4, this is sulfate ion and it is regarded as a polyatomic ion because there is one sulfur and four oxygen atoms and it has a -2 charge.

Polyatomic Formulas – Polyatomic ions are made from more that one atom. This group of atoms act together as one unit with a single charge. Each of the polyatomic ions have a unique name. The formula for the compound will contain both a cation and an anion to balance the overall charge of the compound.

A polyatomic ion is an ion made up of more than one atom that acts like an individual ion. A polyatomic ion exists as a unit so the subscripts of the atoms in the ion do not change.

Rule 1. The cation is written first in the name; the anion is written second in the name. Rule 2. When the formula unit contains two or more of the same polyatomic ion, that ion is written in parentheses with the subscript written outside the parentheses.

The carbonate ion consists of one carbon atom and three oxygen atoms, and carries an overall charge of 2−. The formula of the carbonate ion is CO2−3. The atoms of a polyatomic ion are tightly bonded together, and so the entire ion behaves as a single unit.

High concentrations of hydrogen ions yield a low pH (acidic substances), whereas low levels of hydrogen ions result in a high pH (basic substances). The overall concentration of hydrogen ions is inversely related to its pH and can be measured on the pH scale (Figure 1).

H+

Ions form when atoms gain or lose electrons. Since electrons are negatively charged, an atom that loses one or more electrons will become positively charged; an atom that gains one or more electrons becomes negatively charged. Ionic bonding is the attraction between positively- and negatively-charged ions.