Question

Which category would polar molecules fall under: Arrhenius Acid/Base Bronsted-Lowry Acid/Base Lewis Acid/Base?

I understand what each of the theories mean, but none of them explicitly state anything regarding polar molecules...?

Answer 1

Although not 100% certain, chances are high that such molecules fall into the Lewis Acid/Base category.

Explanation:

Acids

• Arrhenius Acids dissolve to release `H^+` ions (in other words, form `H_3O^+` with water;)
• Bronsted-Lowry Acids act as proton donors so they are in effect the same set of species as Arrhenius Acids;
• Lewis Acids accepts pairs of electrons, and are thus typically either electron-deficient (electrophilic, like `BF_3` in which the central boron atom has only six electrons in its valence shell) or have vacancies in higher orbitals (such as `d` orbital for transition metals like `Cu^2+`, such that they form (colored) complexes/complexions e.g., `[Cu*(6H_2O)]^(2+)`.)

Bases:

• Arrhenius Bases dissolve to release `OH^-` ions;
• Bronsted-Lowry Bases accepts protons and as a result, comprises a superset of Arrhenius bases;
• Lewis bases have at least one lone/non-bonding pair of electrons and form coordinate covalent bonds with acidic species (nucleophilic) and are essentially the same set as Bronsted-Lowry bases.

The question might have assumed that polar species are either electron-deficient (electrophilic) or have extra pairs of non-bonding pairs at spare (nucleophilic). But they might not necessarily dissolve in water to release protons or hydroxide ions (if they contain any hydrogen at all.) Also, there isn't enough information to tell whether the species in question is acidic, basic, or amphiprotic. So Lewis Acid/Bases might be the safest option.