Help! how are elements isotopes and compounds different?

Atoms of one _element_ all have one thing in common -- they have the same number of protons. Atoms of an element can differ in the number of electrons (making them _ions_ of the element) or the number of neutrons (making them _isotopes_). When different elements connect (bond) to each other to make a new substance, we call that a compound. In table salt, for example, we have sodium (an element which is a gray solid at room temperature) and chlorine (another element, which is a gas at room temperature) combining to form a new substance that is a white solid at room temperature. This substance is a compound. What we created the substance from (sodium and chlorine) are elements.