In nature, the element X consists of two naturally occurring isotopes. 107X with abundance 55.84% and isotopic mass 106.9051 amu and 109X with isotopic mass 108.9048 amu. Use the given information to calculate the atomic mass of the element X. How can you find the atomic mass of the element X without knowing the abundance of its isotope 109X?

It is hard to do this because there is some information missing that you must think about. But you can do it. Remember that there are only two isotopes! Let me give you a hint. Suppose I buy a candy bar and split it into two pieces: one for you and one for me. I eat 40% and you get the rest. Can you figure out how much you get? The same must be true for the isotopes.

Good question. One way that ionic compounds can be made is when they contain polyatomic ions. Look up polyatomic ions in the notes. These are molecules that are charged and are made using nonmetals. These atoms like to combine in such a way as to make charged ions. Compounds made from them are ionic. The only way to recognize these polyatomic ions is to memorize the ones in the table in the notes. You might guess the compound is molecular because it only has nonmetal atoms. But the presence of a polyatomic ion makes the compound ionic.