Potassium will have the greatest atomic size because of its number of shells, followed by sodium which 1 valence electron compared to magnesium the same number of shells but 2 valence electrons.
Relative size of the atoms
The relative size of the atoms is determined from the number of shells and valence electron contained in the atom.
Sodium, 11 ----> 2, 8, 1
Magnesium, 12 ----> 2, 8, 2
Potassium, 19, -----> 2, 8, 8, 1,
Potassium will have the greatest atomic size because of its number of shells, followed by sodium which 1 valence electron compared to magnesium the same number of shells but 2 valence electrons.
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