Which one of the following statements is true regarding ionization energies?

• A. Ionization energy decreases as you move up a group in the periodic table.
• B. Ionization energy remains constant for all elements in the same period.
• C. Alkali metals have higher ionization energies than noble gases.
• D. Ionization energy generally increases across a period from left to right.

Answer: (D)

Verified step by step guidance

1. Recall the definition of ionization energy: it is the energy required to remove an electron from a gaseous atom or ion.
2. Understand the general trends in the periodic table: ionization energy tends to increase as you move from left to right across a period because the nuclear charge increases, pulling electrons closer and making them harder to remove.
3. Recognize that ionization energy generally decreases as you move down a group because additional electron shells increase the distance between the nucleus and the outermost electron, reducing the attraction and making it easier to remove an electron.
4. Evaluate the given statements based on these trends: ionization energy does not remain constant across a period, and alkali metals have lower ionization energies compared to noble gases, which have full electron shells and are very stable.
5. Conclude that the true statement is that ionization energy generally increases across a period from left to right, reflecting the increasing nuclear charge and stronger attraction for electrons.