What is the symbol of an ion with 16 protons, 18 neutrons, and 18 electrons?

Solution: The number of protons is equal to the atomic number, which is unique to each element. The atomic number with the symbol can be found on the Periodic Table and is S (sulfur).

Mass number = protons + neutrons = 16+18= 34

To calculate the charge we must know that a proton has a +1 charge and an electron has -1 charge. We get +16-18 = -2