Final answer:
The octet rule is a chemical principle stating that atoms tend to bond in ways that result in eight valence electrons, although exceptions such as hydrogen (duet rule), transition metals, and elements with expanded valence shells exist.
Step-by-step explanation:
Understanding the octet rule is crucial for predicting molecular structure and stability in Chemistry. This rule indicates that atoms tend to form bonds in a way that each atom ends up with eight valence electrons, resembling a noble gas electron configuration. Fluorine (F) from group 7A forms one bond while Oxygen (O) from group 6A forms two bonds, ensuring that each achieves an octet. However, some elements can violate the octet rule. For example, hydrogen follows the duet rule instead, having only two electrons in its valent shell. Elements in the third row and beyond of the periodic table can exceed an octet, having expanded valence shells due to the availability of d orbitals.
It's important to note that, while the octet rule is a guideline, not all elements strictly follow it. Transition metals and inner transition metals often do not adhere to the octet rule, and odd-electron molecules cannot satisfy it. Yet, when looking at ions, achieving an octet can be a driving force for stability. Sodium, for instance, tends to lose one electron to form the Na+ ion with a complete octet in its new valence shell.
Bonding and the pursuit of a stable electron configuration through the octet rule or exceptions to it, such as the duet rule or expanded octets, are fundamental concepts in understanding chemical reactivity and the formation of stable compounds.