Which statement best explains why some atoms have extra electrons in an expanded octet?

• A. Atoms with expanded octets have lost electrons from their core shells, making room for more valence electrons.
• B. Atoms in period 3 and beyond have available d orbitals that allow them to accommodate more than eight electrons in their valence shell.
• C. Atoms with expanded octets have more protons, which attract additional electrons into the valence shell.
• D. Expanded octets occur because the octet rule does not apply to any elements in the periodic table.

Answer: (B)

Verified step by step guidance

1. Understand the octet rule: it states that atoms tend to have eight electrons in their valence shell to achieve a stable electron configuration, similar to noble gases.
2. Recognize that the octet rule primarily applies to elements in periods 1 and 2, which have only s and p orbitals available in their valence shell.
3. Identify that atoms in period 3 and beyond have access to d orbitals in addition to s and p orbitals, which can accommodate extra electrons beyond the typical eight.
4. Explain that these available d orbitals allow such atoms to expand their valence shell and hold more than eight electrons, leading to an expanded octet.
5. Conclude that the presence of accessible d orbitals in period 3 and heavier elements is the key reason why some atoms can have expanded octets, rather than losing core electrons or simply having more protons.