Protons and neutrons are located in which central part of the atom?
radius
shell
nucleolus
nucleus
Electrons have almost no mass. Instead, almost all the mass of an atom is in its protons and neutrons in the nucleus. The nucleus is very small, but it is densely packed with matter. The SI unit for the mass of an atom is the atomic mass unit (amu) . One atomic mass unit equals the mass of a proton, which is about 1.7 × 10 -24 g. Each neutron also has a mass of 1 amu. Therefore, the sum of the protons and neutrons in an atom is about equal to the atom’s total mass in atomic mass units.