Which of the following best describes the overall trend in ionization energy across the periodic table?

• A. Ionization energy remains constant across both periods and groups.
• B. Ionization energy increases from right to left across a period and from top to bottom within a group.
• C. Ionization energy decreases from left to right across a period and from top to bottom within a group.
• D. Ionization energy increases from left to right across a period and from bottom to top within a group.

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), the nuclear charge increases while the shielding effect remains relatively constant, causing electrons to be held more tightly and thus increasing ionization energy.
3. Recognize that down a group (top to bottom), additional electron shells are added, increasing the distance between the nucleus and the outermost electron and increasing shielding, which lowers the ionization energy.
4. Summarize the trend: ionization energy generally increases from left to right across a period and decreases from top to bottom within a group.
5. Compare the given options to this understanding and identify the correct description of the trend.