Why Cobalt has a greater relative atomic mass than nickel?
The answer is in the neutrons… Electrons are practically massless. It is neutrons and protons that contribute to an atom’s mass. In fact, atomic mass = # of protons + # of neutrons. By definition, an atom has no electrical charge. Therefore, an atom always has the same amount of protons as electrons. So we know that cobalt has 27 electrons and 27 protons, and that nickel has 28 electrons and 28 protons. However, the number of neutrons in an atom is not proportional to the number of protons. Cobalt has (on average) 31.933 neutrons per atom. # of neutrons = atomic mass – atomic number. Nickel has 30.693 neutrons per atom. So although nickel has one more proton than cobalt, cobalt has on average 1.3 more neutrons than nickel, which makes it weight more. Hope this helps!
