GRE Subject Test: Chemistry : Lewis, Brønsted-Lowry, and Arrhenius Definitions
Study concepts, example questions & explanations for GRE Subject Test: Chemistry
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Example Questions
Example Question #1 : Acid Base Chemistry
What is the definition of a Brønsted-Lowry base?
A compound that donates an electron pair in solution
A compound that accepts protons in solution
A compound that accepts an electron pair in solution
A compound that donates protons in solution
A compound that accepts protons in solution
A Brønsted-Lowry base is any compound that accepts protons in solution. Lewis acids and bases refer to the accepting or donating of an electron pair, respectively.
Example Question #1 : Lewis, Brønsted Lowry, And Arrhenius Definitions
Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
In the reverse reaction of 
electron donor . . . Brønsted-Lowry base
electron donor . . . Lewis acid
electron acceptor . . . Lewis acid
electron donor . . . Lewis base
electron acceptor . . . Lewis base
electron acceptor . . . Lewis acid
In terms of the passage, the lone proton can be considered a proton donor and would, therefore, be a Brønsted-Lowry acid. This is not an answer choice.
The third acid-base definition is the Lewis definition, which states that acids are electron acceptors and bases are electron donors. The negative charge on the 
Example Question #2 : Lewis, Brønsted Lowry, And Arrhenius Definitions
Which of the following molecules or ions have the greatest ability to act like a Lewis acid?
Lewis acids are electron pair acceptors. Molecules and ions that have a full octet cannot act a Lewis acid, therefore 
Example Question #1 : Lewis, Brønsted Lowry, And Arrhenius Definitions
Which of the following is not a strong electrophile?
All of these are strong electrophiles.
One of the easiest ways of determining if a molecule is an electrophile is by the presence of a positive charge. Electrophiles are in need of electrons, therefore they are electron deficient and can be attacked by nucleophiles (compounds that are electron rich). A nucleophile is a compound that provides a pair of electrons to form a new covalent bond. Nucleophiles are electron rich and one of the easiest types of nucleophiles to recognize are ones carrying a negative charge. 
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