Answer:
Order of increasing ionic radius starting from the smallest is
Mg2+ < Na+ < F- < O2- < N3-
Explanation:
Ionic radius is the distance between the nucleus and the electrons in the outermost shell of an ion. In the ions given about, it can be deducted that they all have the same number of electrons and are said to be isoelectronic. This shows us that they all have the same electrons and we can only seperate them by checking the respective charges on the ions. A more positive charge will have a smaller radius while a more negative will have a larger radius. This is because when an atom loses an electron and form a cation (+), the remaining electrons move closer to the nucleus and hence a smaller radius of the atom occurs. But when an atom gains n electron,it forms anion (-), the new electron leads to the shielding of the remaining electrons from the nucleus and a large radius of the atom occurs.
So therefore, the above ions all have 10 electrons in their shells and magnesium with atomic number 12 and having lost 2 electrons to become positively charge has the smallest radius compared to others.
Mg2+ = 12 protons, 10 electrons
Na+ = 11 protons, 10 electrons
F- = 9 protons, 10 electrons
O2- = 8 protons, 10 electrons
N3- = 7 protons, 10 electrons
N3- has the largest ionic radius and Mg2+ has the lowest ionic radius.
The order is thus, Mg2+ , Na+, F-, O2-, N3-
