Rank the following elements in order of decreasing atomic radius.

Rank from largest to smallest radius. Si, Mg, Na, Al

The rank of the elements in order of decreasing atomic radius is:

Si < Al < Mg < Na

Explanation:

You can compare elements in a same column (group) or in a same row (period) of the periodic table to predict their relative atomic radius, using the periodic tendencies.

Silicon (Si), magnesium (Mg), soidum (Na), and aluminum (Al) are in the same period (row) number 3.

The order in which they are, from left to right, is:

Na (Z = 11), Mg (Z = 12), Al (Z = 13), Si (Z = 14).

As the atomic number (Z) increases, the number of protons in the nucleus increases.

Since, the elements are in the same period, the principal quantum number or main energy level, does not change.

That means that, when you go from left to right in the row, the force of attraction (due to more protons and more electrons) incrases, while the outermost shell is the same.

Then, that increase in the attraction force leads to the electrons be closer to the nucleus of the atom, which means the atomic radius decreases.

Thus, you conclude that the rank of the elements in order of decreasing atomic radius is:

Si < Al < Mg < Na