Protons: 81 Neutrons: 120
Work Step by Step
The atomic number, as shown by the periodic table, of Thallium is 81, meaning that there are 81 protons (the atomic number is the number of protons). Because it is Thallium-201, the atomic mass number of this isotope is 201 amu. Because both protons and neutrons weigh one amu while electrons are essentially weightless, this means that there must be 120 neutrons (81 protons+120 neutrons= 201 amu).