Think about a neutral magnesium atom. Then think of a magnesium ion with a 2+charge. How are these two alike? How are they different? Be sure to use the terms proton, neutron, and electron in your answer.

All atoms of the same element have the same number of protons. Magnesium has the atomic number 12, so both atoms have 12 protons in their nucleus. As long as both are of the same isotope of magnesium (have the same sum of protons and neutrons), they both will have the same number of neutrons. Regardless, the neutrons do not influence their charges, so the number of neutrons does not make much of a difference at this level. The difference between the two is their charge. Since a charge difference only happens by a change in electrons, the negatively charged particles, their number of electrons must be different. The charge equals: (number of protons) - (number of electrons) = charge

Therefore, since both particles have 12 protons, the neutral atom has:

#protons - #electrons = 0

12 - #electrons = 0

number of electrons = 12 in the neutral magnesium atom

In a positively charged ion, the equation is:

#protons - #electrons = 2

12 = 2 + #electrons

#electrons = 10 in the 2 + charged magnesium atom