Which direction on the periodic table has the least ionization energy and the lowest electronegativity?

• A. Top right
• B. Top left
• C. Bottom left
• D. Bottom right

Answer: (C)

Ionization energy and electronegativity both follow clear trends: they generally decrease as you move down a group and increase as you move across a period from left to right. When you go down a column, atoms get larger and have more shielding from inner electrons, so the outer electrons feel less pull from the nucleus and require less energy to remove. The same enlargement and shielding also make the atom less effective at attracting electrons in a bond, lowering electronegativity. Across a period, protons are added with electrons occupying the same shell, which increases the effective nuclear charge felt by the valence electrons; this pulls them in more tightly and makes it harder to remove an electron and to attract bonding electrons, raising both ionization energy and electronegativity.

Putting those trends together, the direction that has the smallest ionization energy and the smallest electronegativity is the bottom-left region of the table. This area contains highly electropositive metals with the least tendency to attract electrons in bonds.