Valency and Polarity in Molecules?

📌 CONCEPT: Valency refers to the combining capacity of an atom in a chemical reaction, while polarity in molecules arises due to the unequal sharing or distribution of electrons between atoms, resulting in a net dipole moment.

📐 RULE / FORMULA: The key principle here is that a molecule with a non-zero net dipole moment can have a non-zero valency, even if the atoms share electrons equally, due to the presence of a lone pair or a distorted electron cloud.

💡 WORKED EXAMPLE: Consider a molecule of H2O, where oxygen shares its 2 electrons with two hydrogen atoms. Although the electrons are shared equally, the lone pair on the oxygen atom creates a distorted electron cloud, resulting in a net dipole moment and a non-zero valency. This is despite the fact that oxygen shares its electrons equally with hydrogen atoms.

⚠️ COMMON MISTAKE: Students often confuse valency with polarity and assume that equal sharing of electrons between atoms means zero valency. However, valency is a measure of an atom's combining capacity, which can be influenced by factors like lone pairs and electron cloud distortion.