Final answer:
Nucleophiles can act as Brønsted-Lowry bases because they can accept a H+ (proton), with a common example being NH3, which accepts a proton on its lone pair of electrons. Other molecules and ions with lone pairs can also qualify as Brønsted-Lowry bases, such as OH- and CH3COO-.
Step-by-step explanation:
Nucleophiles can behave as Brønsted-Lowry bases because of their ability to pick up a H+. A nucleophile is a species that can donate a pair of electrons to form a covalent bond, and as such, when it accepts a proton (H+), it is acting as a base. For instance, with NH3 (ammonia), the nitrogen (N) atom can accept a proton onto its lone electron pair, thus functioning as a Brønsted-Lowry base. A substance like NH2-, which can accept a proton to become NH3, would also be considered a Brønsted-Lowry base.
A Brønsted-Lowry base is defined as a proton acceptor, which differentiates it from Brønsted-Lowry acids that donate protons. A molecule or ion with available lone pairs of electrons, such as the hydroxyl ion (OH-) or the acetate anion (CH3COO-), can act as a Brønsted-Lowry base by accepting a hydrogen ion. Certain compounds, like water (H2O), are amphiprotic, meaning they can act as either a Brønsted-Lowry acid or base depending on the situation.