An example of a molecule exhibiting an expanded octet is sulfur hexafluoride (SF6).
Understanding the Expanded Octet
The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a full outer electron shell containing eight electrons. However, elements in the third period and beyond can sometimes accommodate more than eight electrons around them, leading to what is known as an expanded octet or hypervalency. This occurs because these elements have available d-orbitals that can participate in bonding.
Sulfur Hexafluoride (SF6) as an Example
In sulfur hexafluoride (SF6), the central sulfur atom is bonded to six fluorine atoms. Each sulfur-fluorine bond involves a shared pair of electrons. Consequently, the sulfur atom is surrounded by 12 electrons (6 bonds x 2 electrons/bond), exceeding the typical octet of 8 electrons.
Other Examples
Besides SF6, another common example is phosphorus pentachloride (PCl5), where phosphorus has 10 electrons surrounding it. These compounds demonstrate that the octet rule is not universally applicable, especially for elements in the third row and beyond. The availability of d-orbitals allows these elements to form more than four covalent bonds.
