Why do ionization energies increase from left to right across any period?

Question

Jeremiah Adams · Accepted Answer

Because of increasing nuclear charge, #Z#.

While going from left to right, we are adding electrons, as well as protons, electrons are entering the same shell, and the electrons do not shield each other effectively. The valence electrons experience an effectively larger nuclear charge going to the right of the Period. Ionization energies should progressively increase. Do they?

Ionization Energy
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What do you think the above effect will have on ATOMIC size?

Ionization Energy
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What do you think the above effect will have on ATOMIC size?

Noah Aldrich · Answer

undefined Ionization energies increase from left to right across any period because as you move from left to right, the number of protons in the nucleus increases, resulting in a greater nuclear charge. This increased nuclear charge exerts a stronger pull on the valence electrons, making it more difficult to remove them from the atom, thus requiring more energy to ionize the atom.