Harry, take a look in that chapter of the book and in any notes you may have taken for it and scan for Einstein. Wherever you see his name, underline it in pencil. Once you find his explanation, think about how he said it. You know an element is one of the most basic things in chemistry, that it is what helps to make up all other things, but what did Einstein mean by his particular description? Take it step by step, listing the qualities he spoke of, and figure how you can put it into formulae. Eliminate from your mind the things that don't fit, and don't try to make something fit that doesn't, until you can think of those that work and write them down.
Without being able to see what he said, I cannot help you further.