Polyatomic ionic compounds will have more than 2 ions in it. In most polyatomic compounds, 1 ion will be metal and the remainder will be non-metals. As always, refer to the periodic table to find the names of each ion. Let's say you're working with the following compound: FeNH4(SO4)2. First, the SO4 ion has a charge of -2. You also know that there are two of these ions because of the “2” below the parenthesis. This ion is called “sulfate” because it’s a combination of oxygen and sulfur. So, 2 x -2 = -4. Then, the NH4, or the ammonium ion, has a charge of +1. You can figure out that it has this positive charge since ammonia itself is neutral, and ammonium contains 1 additional hydrogen molecule. (Ammonium is so-called because it combines 1 nitrogen molecule with 4 hydrogen molecules.) Add -4 and 1 and you get -3. This means that the iron ion, Fe, must have a charge of +3 to make up for it and to make the compound neutral.  Ionic compounds always have a neutral charge. You can use this information to calculate the metal’s charge. SO4 has a charge of -2 since it’s negative without the 2 hydrogen atoms that it had when it existed as sulfuric acid. The way you write the name will vary based on whether you’re using the newer or older naming method. So, to name the metal ion, either write Iron (III) or ferric. Refer to the periodic table to remind yourself that “S” is sulfur. Ammonium is not an element, but occurs when 1 nitrogen ion combines with 4 hydrogen ions. So, you're working with ammonium and sulfate, or ammonium sulfate. “Ammonia” becomes “ammonium” when it takes on a positive charge. Ammonia itself is neutrally charged. You can name the compound FeNH4(SO4)2 by writing iron (III) ammonium sulfate. If you’re required to use the older naming method for ionic compounds, write ferric ammonium sulfate.

How would you rephrase that briefly using Vietnamese?
Viết công thức của ion đa nguyên tử. Tìm điện tích kim loại. Viết tên kim loại. Viết tên ion phi kim. Kết hợp tên kim loại và tên các ion phi kim.