1. Identify the element described Noble gas in period 2 Alkali metal in period 4 Halogen in period 4 B. Isotopes Atoms are made up of protons, neutrons, and electrons. The nucleus contains the protons and the neutrons. The electrons are found circling around the nucleus in various molecular orbitals. Protons have a mass of 1 atomic mass units (amu) and are positively charged. The neutron also has a mass of 1 amu, but is neutral. The electron has negligible mass and is negatively charged. The identity of any atom is based on the number of protons and is also the atomic number of that atom. Since the proton has a positive charge, there should be an equal number of electrons for a neutral atom. The mass number of any atom is based on the number of protons and neutrons. Varying amounts of neutrons give rise to isotopes. The number of neutrons is equal to the mass number minus the atomic number Complete the following table by filling in any missing information. Each of the isotopes described are used in medicine. Complete Symbol Medical Use Atomic Number Mass Number # Protons # Neutrons # Electrons 123/53 Image thyroid, brain, heart, and kidney 53 53 201TI Image heart and diagnose and heart attack 201 81 81 Detect pancreatic cancer 68Ga 31 2. Write the complete symbol for an element with 35 protons and 46 neutrons. 3 CHM 130 Exercise 3 - Atomic Structure