What happens to ionization energy as you move from left to right across a period?

As you move from left to right across a period in the periodic table, ionization energy generally increases. This trend occurs because the atoms have more protons in their nucleus as you move across a period, leading to a greater positive charge. The increased nuclear charge attracts the electrons more strongly, making it harder to remove an electron from the outer shell. Consequently, more energy is required to overcome this attraction, resulting in a higher ionization energy.

Moreover, the electrons are added to the same principal energy level as you move across a period, which does not significantly increase the shielding effect compared to the increase in nuclear charge. This reinforces the trend of increasing ionization energy across the period. Overall, the combination of increasing nuclear charge and relatively constant shielding effects contributes to the observed increase in ionization energy.