Which of the following best describes the pattern of the first five ionization energies of an element across a period in the periodic table?

• A. They remain constant across a period.
• B. They increase and then decrease irregularly across a period.
• C. They generally decrease from left to right across a period.
• D. They generally increase from left to right across a period.

Answer: (D)

Verified step by step guidance

1. Understand that ionization energy is the energy required to remove an electron from a gaseous atom or ion.
2. Recall that across a period (left to right) in the periodic table, the nuclear charge increases because more protons are added to the nucleus.
3. Recognize that as nuclear charge increases, electrons are held more tightly by the nucleus, making it harder to remove an electron, which generally increases ionization energy.
4. Note that although there are small irregularities due to electron configurations (such as half-filled or fully filled subshells), the overall trend is an increase in ionization energy across a period.
5. Therefore, the pattern of the first five ionization energies generally shows an increase from left to right across a period.