Acid
MCAT glossary · Chemical & Physical Foundations of Biological Systems
Definition
A species that donates a proton (Brønsted–Lowry) or accepts an electron pair (Lewis).
Acid in plain English
An acid is a chemical that likes to 'give something away' to other molecules — which is why acids feel chemically aggressive (think lemon juice or stomach acid). In the most common view (Brønsted–Lowry), an acid hands off a proton, which is just a hydrogen atom stripped of its electron (H^+). In a broader view (Lewis), an acid instead grabs a shared pair of electrons from a partner. Either way, the theme is the same: an acid is the molecule doing the 'taking' in these little exchanges, and that hunger is what drives acid chemistry.
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