Polyatomic ions are covalently bonded atoms that together have a net charge and act as an ion. When naming compounds with polyatomic ions, add the name of the polyatomic ion as it is into the name of the ionic compound. For example, let's name Fe2SO43. SO4 is the polyatomic ion sulfate. Iron is a Type Two metal, so we need to use the charge of sulfate to determine the charge of iron. We know the formula unit is overall neutral, so two times the charge of iron plus three times the charge of sulfate equals zero. Sulfate has a two minus charge, so solving for iron, we see that it has a three plus charge. So the name of our ionic compound is iron three sulfate. We can also name NH4Br. NH4+ is ammonium; we can add the name of the polyatomic ion as it is when naming the compound. So our ionic compound is ammonium bromide. Oxyanions are polyatomic anions that contain oxygen and one other element. When naming oxyanions, they follow a predictable pattern depending on the number of oxygen atoms relative to the -ate ion. For example, bromate is BrO3-. If we add an oxygen atom to the -ate ion without changing the charge, we add the prefix per- to the front of the name. So BrO4- is perbromate. If we remove one oxygen atom from the -ate ion without changing the charge, we change the ending from -ate to -ite. So BrO2- is bromite. If we remove one more oxygen atom from the -ite ion, we add the prefix hypo-, so BrO- is hypobromite. Iodate follows a similar pattern. If we add an H+ to an oxyanion and the resulting ion still has a negative charge, we name the ion by adding hydrogen out front. For example, PO4 3- is phosphate. If we add an H+ to phosphate, it becomes HPO4 2-. Notice that the charge is one less negative because we added an H+. The name becomes hydrogen phosphate. If we add one more H+ to form H2PO4-, the name becomes dihydrogen phosphate. This table contains common polyatomic ions. We can see our patterns at work for naming. For example, nitrate is NO3- and nitrite is NO2-. We see the same pattern with the chlorate series and with sulfate and sulfite. We can also see our pattern of adding H+ with phosphate, sulfate, sulfite, and carbonate. Since naming is a fundamental skill, we'll want to know the formula, including charge, for our polyatomic ions. Let's practice naming ionic compounds with polyatomic ions. For CuSO4, copper is a Type Two metal, so we need to determine its charge. We know the formula unit is overall neutral, so the charge on one copper plus the charge of sulfate is equal to zero. We know that the charge on sulfate is -2, so the charge of copper must be 2+. Our compound is copper two sulfate. For Mg3PO32, magnesium is a Type One metal, so we don't need to include its charge in the name. PO3 is not on our list of polyatomic ions, but PO43- is phosphate. PO32- has one less oxygen atom, so it should be phosphite. So our compound is magnesium phosphite. For PbCO32, lead is a Type Two metal, so we need to determine its charge. We know our formula unit is overall electrically neutral, so the charge on one lead ion plus two times the charge of carbonate equals zero. The charge of carbonate is -2, so the charge on lead must be +4. Our compound is lead four carbonate. In our last example, calcium is a Type One metal, so we don't need to include its charge in the name. To determine the name of our polyatomic ion, we know iodate is IO3-. If we remove one oxygen atom from iodate, we have iodite. If we remove one more oxygen atom, we have IO-, which is hypoiodite. So our compound is calcium hypoiodite. Hydrates are ionic compounds that have a specific number of water molecules associated with each formula unit. The water molecules can typically be removed by heating. For example, cobalt two chloride hexahydrate has six water molecules associated with each formula unit. This hydrate is a reddish color; when it's heated, the water molecules can be removed to leave just cobalt two chloride, and it changes to a purple color. When we name hydrates, we name the ionic compound normally and add hydrate to the end of the name with a prefix indicating how many water molecules are associated with each formula unit. Our prefixes range from hemi for ½ to octa for 8. If we name CuSO4 5H2O, our ionic compound is copper two sulfate. Since there are five water molecules associated with each formula unit, we add pentahydrate. So our hydrate is called copper two sulfate pentahydrate.