Base (chemistry)
Substance that reacts with acids; accepts protons or donates electrons.
In chemistry, a base is a substance that reacts with acids, a concept originally proposed by G.-F. Rouelle in the mid-18th century. Three definitions are commonly used: Arrhenius bases, Brønsted bases, and Lewis bases, each describing bases as substances that accept protons or donate electron pairs.
- lewis_theory_proposed_by
- G. N. Lewis
- common_properties
- slippery to touch, bitter taste, pH > 7, turn red litmus blue
Lore & Background
Arrhenius bases are metal hydroxides such as NaOH or Ca(OH)2. G. N. Lewis later defined a base as an electron pair donor, a more general concept that includes non-proton acceptors like boron trifluoride.
Reader's Guide
Bases are fundamental to acid–base chemistry, with three major definitions reflecting increasing generality. The Arrhenius definition applies to aqueous solutions, where bases produce hydroxide ions. The Brønsted–Lowry definition extends to any proton acceptor, including ammonia, which reacts with water to increase hydroxide concentration. The Lewis definition is the most general, encompassing any electron pair donor, such as water or ammonia, that can bond with an electron acceptor. Bases react with acids in neutralization reactions, producing water and a salt. They have characteristic properties: slippery feel, bitter taste, pH above 7, and they change the color of indicators (e.g., turn red litmus blue). Strong bases are caustic and conduct electricity when dissolved. The equilibrium constant Kb measures base strength; weaker bases have lower Kb values. The concept originated from alchemical notions of a 'matrix' and was formalized by Rouelle in the 18th century. Understanding bases is essential for fields ranging from industrial chemistry to biochemistry.
Did You Know?
- Arrhenius bases are a subset of Brønsted bases, as both involve hydroxide ions or proton acceptance.
- Lewis bases can share an electron pair with an acceptor that is not necessarily a proton, such as boron trifluoride.
- A soluble base that releases OH− ions quantitatively is called an alkali.
Frequently Asked Questions
What is a base in chemistry?
A base is a chemical substance whose core behavior is neutralizing acids, and more broadly, accepting protons or donating electron pairs to other molecules.
Who originally proposed the concept of a base?
The idea of a base as a distinct class of substance was first articulated by G.-F. Rouelle in the mid-1700s, and G. N. Lewis later broadened the definition to include electron-pair donation.
What properties identify a substance as a base?
Bases typically feel slick or slippery on the skin, taste bitter, register a pH above 7, and cause red litmus paper to shift to blue.
What are the three major theories that define a base?
The three standard frameworks are the Arrhenius definition (produces hydroxide ions in water), the Brønsted–Lowry definition (accepts a proton), and the Lewis definition (donates an electron pair).
Why is the base concept central to chemistry fundamentals?
Without a clear notion of a base, chemists would lack a unifying way to describe neutralization reactions, buffer systems, and a wide range of biological and industrial processes.
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