# Is there an algorithm for ascertaining the relative size of an atomic/ionic radius?

To the best of my knowledge, the following properties affect atomic radius.

1. The grounded-state size of the valence electron shell.
2. The Coulomb force of the core electrons less the Coulomb force of the protons.
3. The number of electrons in the valence shell.
4. Whether an electron#-proton# imbalance is sufficient to change the size of the valence electron shell.

Question 1. Are there any other factors that I should know for Chem. 101?

Question 2. If I were to estimate the size of an atom's radius relative to the radii of the atoms described on the periodic table, I would proceed thus:

1st: Ascertain the grounded-state size of the valence electron shell (i.e. the row of the element in the periodic table).

2nd: If the thing in question is an ion, then adjust the number of electrons accordingly.

3rd: If the adjustment in the second step removed, or added, enough electrons to the atom to eliminate the valence energy shell, or to create a new valence electron shell, then adjust the electron configuration accordingly.

Steps 1-3 give the size of the electron shell, and so give the period that comprises the atoms most comparable by radius size.

4th. For the atom/ion under consideration, and for each element listed in the relevant period, subtract the Coulomb force of the protons from the Coulomb force of the core electrons. The lesser the value of the difference the smaller the size of the atomic radius.

5th. If steps 1-4 produce the same value for the atomic radii of the atom/ion under consideration and for one or more of the relevant elements, then the largest atomic radius characterizes the comparate whose valence electron shell comprises the most electrons.

Is that correct?