How much? 3

How much? 3

1. The Mass of Atoms 3.1

   • protons and neutrons have the same mass
     • mass = 1
     • total number of these is called the mass number
   • mass of electron is very small
     • mass of atom is mostly protons and neutrons
   • there can be different numbers of neutrons in atoms of the same element
     • these are called isotopes
     • mass number - atomic number = number of neutrons