Sometimes, more than one element can combine to form an ion, which can then bond with a different ion to form a compound. For example, OH−1{\displaystyle OH^{-1}} is a polyatomic ion made from oxygen and hydrogen ions. Each polyatomic ion has its own special name. OH−1{\displaystyle OH^{-1}} is called "hydroxide."   OH−1{\displaystyle OH^{-1}} is not an ionic compound, because it does not have a net charge of zero. It is a single ion, which can combine with ions of the opposite charge. Some elements can form polyatomic ions by themselves. For example, "peroxide" is the O22−{\displaystyle O_{2}^{2-}} ion. It contains 2 oxygen atoms, but has a total charge of -2. (This is different than oxide, the "standard" oxygen ion, which has one atom with a charge of -2.) The second word in the ionic compound's name refers to the polyatomic ion. Look up this word (not the full compound name) to find the formula for this polyatomic ion. You can also memorize a few common polyatomic ions:  Cyanide: CN−{\displaystyle CN^{-}} (One carbon, one nitrogen, total charge of -1) Hydroxide: OH−{\displaystyle OH^{-}}. Nitrate: NO3−{\displaystyle NO_{3}^{-}} (One nitrogen, three oxygen, total charge of -1) Nitrite: NO2−{\displaystyle NO_{2}^{-}}  Peroxide: O22−{\displaystyle O_{2}^{2-}}  Sulfate: SO42−{\displaystyle SO_{4}^{2-}}  Sulfite: SO32−{\displaystyle SO_{3}^{2-}} The other ion in the compound is usually a simpler, one-atom ion. You can find its charge the same way you would in any problem. For example, magnesium hydroxide contains a magnesium cation. Magnesium is a group 2 element that forms the ion Mg2+{\displaystyle Mg^{2+}}. All ionic compounds have a total net charge of zero. Find the minimum number of positive and negative ions that balance each other's charges perfectly. Remember that the polyatomic ion is a single ion, and cannot be divided into parts. For example, to balance OH−1{\displaystyle OH^{-1}} and Mg2+{\displaystyle Mg^{2+}} , compare the charges. It takes two -1 charges to balance out one 2+ charge. This means there are two hydroxide ions and one magnesium ion. To show that there are multiple polyatomic ions, enclose that section of the formula in parentheses. Write the subscript showing the number of atoms after the close parenthesis.  In the case that more than one of a certain polyatomic ion is necessary to balance the charge, the entire formula for the polyatomic ion is enclosed in parentheses and the numerical subscript is placed outside the parentheses. This shows that the subscript applies to the entire polyatomic ion.  For example, magnesium hydroxide has the chemical formula Mg(OH)2{\displaystyle Mg(OH)_{2}}. You do not need to include the charges of the ions.

Summary: Understand polyatomic ions. Look up the chemical formula for the polyatomic ion. Find the charge of the other ion. Balance the charges of the 2 ions. Write the formula.


Wrap up from the base at least 3 feet (0.9 m). This will keep the beavers from being able to eat or use the trees. You will need to check your trees to make sure that the beavers are leaving them alone. You can also make wire fences to prevent beavers from entering a specific area (especially around a pond). You can also put mesh coverings over culverts and the like to keep beavers away from them. Sometimes completely destroying the beaver's dam or lodge, as well as eliminating access to its habitat can discourage the beaver. You have to make sure that you carry away all of the dam, so that the beaver can't access it in order to rebuild.  Use a sturdy potato rake and work from the downstream side, to completely destroy the dam or lodge. You will want to keep checking the dam or lodge area to make sure that the beaver is not rebuilding and that there is no material available for rebuilding. There is only one repellant that has been proven to be effective in eliminating beavers and beaver damage. This is Thiram. You'll need to apply the repellant directly to the leaves and shrubs that the beaver has been using as a food source.  Again it's good to use this method in conjunction with the other methods, such as destroying the dams and lodges and then spraying the food sources with Thiram. There are other repellants and sprays you can use to discourage beavers from coming into the area if they haven't already, but only Thiram gets rid of them if they're already there. There are a couple different ways to control the water level so that it doesn't become conducive to beaver habitation. You can create a drain so that the water level stays down or you can keep the water clear of debris or anything that might prevent water flow.  Get a drain pipe by fitting two plastic sewer pipes together and perforate one of them. Depending on the volume of the water in the stream the diameter of the pipes can be 10, 15, 20 or 25 cm (4, 6, 8 or 10 in.). Dig a hole in the beaver dam along the original stream channel. Set three-quarters of the pipe at almost any level in the dam, and extend the perforated edge into the beaver pond (upstream). Attach a weight to one end of the pipe. Allow around one quarter of the pipe to extend out on the downstream side of the dam. Add about a 1 inch elbow or turndown to the perforated side of the pipe so that you discourage plugging of the upstream end of the pipe.
Summary: Wrap trees with chicken wire or other heavy metal sheeting or wire. Destroy the dam or lodge. Use a repellant. Control the water level.