Electrons orbit around the nucleus of atoms in allowed energy states. this is the basis of the theory of which scientist?
a. john dalton
b. niels bohr
c. albert einstein

Sally is making a model of a magnesium atom with an atomic mass number of 24 for her chemistry class. she has foam balls for the protons, neutrons, and electrons. she has added 6 neutrons to her model so far. how many more neutrons does she need to add to complete her neutral atom of magnesium?