Question

explain in your own words why ionization energy increases as atomic number increases across the periodic table.

Explanation:

As atomic number increases across a period (left to right on the periodic table), the number of protons in the nucleus increases. This increases the positive nuclear charge. At the same time, electrons are added to the same principal energy level (shell), so the shielding effect from inner electrons doesn't increase significantly. The increased nuclear charge pulls the outermost electrons more strongly towards the nucleus, making them more tightly held. To remove an electron (ionization), more energy is needed because the electron is closer to the nucleus and experiences a stronger attractive force.

Answer:

Ionization energy increases across a period (with increasing atomic number) because nuclear charge increases (more protons), electrons add to the same energy level (so shielding doesn’t increase much), and the outermost electrons are pulled more strongly by the nucleus, requiring more energy to remove them.