The periodic table will give us the atomic number of an element. The atomic number tells us how many protons an atom has. Based on the previous description of the atom, draw a model of the hydrogen atom. You will learn later that while this is a nice way to learn about the structure of atoms, it is not the most accurate way to model them. Different forms of the same chemical element that differ only by the number of neutrons in their nucleus are called isotopes .
Most elements have more than one naturally occurring isotope.
Many more isotopes have been produced in nuclear reactors and scientific laboratories. Isotopes usually aren't very stable, and they tend to undergo radioactive decay until something that is more stable is formed. The 235 means that this form of uranium has 235 neutrons and protons combined. If we looked up uranium's atomic number, and substracted that from 235, we could calculate the number of neutrons that isotope has. Use the periodic table and the names of the elements given below to figure out how many protons, neutrons and electrons they have.