Certainly! The term "expanded octet" refers to the ability of an atom to have more than eight electrons in its valence shell. This typically occurs with elements that have available d-orbitals, which allow them to accommodate additional electrons beyond the usual octet rule.
To determine in which period an atom can exhibit an expanded octet, we note:
1. An expanded octet generally occurs in elements of period 3 and beyond. This is because period 3 is the first period in the periodic table where d-orbitals become available (starting from the 3d orbital).
With this in mind, let's analyze each option provided:
- Period 1:
- This period contains hydrogen and helium. They do not have d-orbitals and follow the duet rule (a maximum of 2 electrons).
- Period 2:
- This period includes elements like lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine. Like period 1 elements, period 2 elements do not have access to d-orbitals and adhere strictly to the octet rule (a maximum of 8 electrons in their valence shell).
- Period 3:
- This period starts with sodium and includes elements like magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, and argon. Starting from phosphorus, these elements have vacant 3d orbitals that allow them to accommodate more than 8 valence electrons, demonstrating the possibility of an expanded octet.
- Period 4:
- This period contains potassium and beyond, up to krypton. Elements in this period also have access to d-orbitals (4d) and can accommodate more than 8 electrons in their valence shell.
Therefore, the earliest period where an expanded octet is possible is:
- Period 3
So, the correct answer is: Period 3
