Why is hydroxide written as OH1- and not OH2?
The Correct Answer and Explanation is :
The hydroxide ion is represented as ( \text{OH}^- ) (not ( \text{OH}_2 )) due to its chemical structure and the nature of the ion itself. The hydroxide ion consists of one oxygen atom covalently bonded to one hydrogen atom. The “1” in ( \text{OH}^1 ) indicates the negative charge of the ion, while the subscript indicates how many of each atom are present.
Chemical Structure:
In the hydroxide ion, oxygen has six electrons in its valence shell and requires two more electrons to achieve a stable octet configuration. The hydrogen atom contributes one electron to the bond, allowing oxygen to share this electron, forming a covalent bond. However, oxygen still has an incomplete octet and thus retains a negative charge due to having gained an additional electron from another atom or molecule, leading to the overall charge of ( -1 ).
Ionic Representation:
When discussing ions, it’s crucial to distinguish between the formula for the neutral molecule and the ion itself. ( \text{OH} ) is the formula for the hydroxyl radical, a neutral species with one hydrogen and one oxygen. However, when this species gains an extra electron, it becomes negatively charged, thus forming the hydroxide ion ( \text{OH}^- ).
Misinterpretation of ( \text{OH}_2 ):
Writing hydroxide as ( \text{OH}_2 ) might suggest that there are two hydroxyl groups present, which is misleading and incorrect. It could imply a neutral molecule with a different bonding situation or possibly suggest that two hydrogen atoms are bonded to a single oxygen atom, which is not the case for hydroxide.
In summary, ( \text{OH}^- ) accurately reflects the structure and charge of the hydroxide ion, indicating one oxygen atom, one hydrogen atom, and a single negative charge, while ( \text{OH}_2 ) does not correctly represent the species in question.