Structure & Reactivity in Chemistry
Concepts of Acids and Bases
AB13. Effects on Basicity (Attraction for Proton)
All of the factors that we have discussed for Bronsted acidity, or the ability of a compound to provide a proton to its surroundings, have an effect on basicity as well. In other words, factors like nuclear charge / electron affinity influence how strongly a compound will attract or bind a proton.
the higher the electron affinity or core charge of an atom, the less likely it is to donate its electrons to a proton.
the greater the delocalization of electrons that could potentially donate to a proton, the less able they are to donate.
the greater the electron-withdrawing effects in another part of a molecule, the less likely the electrons on a particular atom are to donate.
These factors are generally complementary to the effects on acidity. A factor that makes a Bronsted acid more acidic usually makes the corresponding conjugate base less basic.
However, sometimes things can be more subtle.
the higher the polarizability of an atom (i.e. the larger an atom), the more easily it can donate to a Lewis acid (its electrons are not held very tightly because they are far from the nucleus, and so they can be donated easily).
except: a larger atom cannot donate easily to a proton. In this specific case, the Lewis acid (the proton) is too small to get good covalent overlap with the Lewis base, so it can't form a very strong bond
Rank the following in terms of base strength (1 = strongest base).
This site is written and maintained by Chris P. Schaller, Ph.D., College of Saint Benedict / Saint John's University (with contributions from other authors as noted). It is freely available for educational use.
Structure & Reactivity in Organic, Biological and Inorganic Chemistry by Chris Schaller is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.
Send corrections to firstname.lastname@example.org
Back to Acidity Index
Back to Structure & Reactivity Web Materials
Back to Chemistry
Back to CSB/SJU