Which of the following best explains why alkali metals lower in the periodic table are more reactive than those higher up?

• A. They have larger atomic radii, making it easier to lose their outermost electron.
• B. They have more protons, which makes their nuclei more attractive to electrons.
• C. They have higher ionization energies, so they react more readily.
• D. They have smaller atomic masses, allowing for faster reactions.

Answer: (A)

Verified step by step guidance

1. Understand that alkali metals are elements in Group 1 of the periodic table, characterized by having one electron in their outermost shell.
2. Recall that reactivity in alkali metals is largely determined by how easily they can lose this outermost electron to form a positive ion (cation).
3. Recognize that as you move down the group, the atomic radius increases because additional electron shells are added, which places the outermost electron farther from the nucleus.
4. Know that the increased distance and shielding effect from inner electrons reduce the effective nuclear attraction on the outermost electron, making it easier to remove (lower ionization energy).
5. Conclude that larger atomic radii and lower ionization energies explain why alkali metals lower in the periodic table are more reactive, as they lose their outermost electron more readily.