Which row and below can have more than 8 electrons in the valence shell, allowing an expanded octet?

Which row and below can have more than 8 electrons in the valence shell, allowing an expanded octet?

• A. First
• B. Second
• C. Fourth
• D. Third

Answer: (D)

Expanded octet happens when the valence shell can use d orbitals in addition to s and p. That capability first appears starting with the third row of the periodic table, because elements in the first and second rows have only s and p valence orbitals and thus max out at eight electrons. From the third row onward (and in higher rows as well), the available d orbitals let the central atom accommodate more than eight electrons around it, producing an expanded octet—as seen in examples like sulfur in SF6 or phosphorus in PF5. Since the earliest row that can have this is the third, that is the correct choice.

Expanded octet happens when the valence shell can use d orbitals in addition to s and p. That capability first appears starting with the third row of the periodic table, because elements in the first and second rows have only s and p valence orbitals and thus max out at eight electrons. From the third row onward (and in higher rows as well), the available d orbitals let the central atom accommodate more than eight electrons around it, producing an expanded octet—as seen in examples like sulfur in SF6 or phosphorus in PF5. Since the earliest row that can have this is the third, that is the correct choice.