What type of substance accepts an electron pair

It is especially important that you know the precise meanings of all the highlighted terms in the context of this topic.

But as with any such theory, it is fair to ask if this is not just a special case of a more general theory that could encompass an even broader range of chemical science. In , G. Lewis of the University of California proposed that the electron pair is the dominant actor in acid-base chemistry. According to Lewis,. In modern chemistry, electron donors are often referred to as nucleophiles, while acceptors are electrophiles.

Although we do not really need to think about electron-pair transfers when we deal with ordinary aqueous-solution acid-base reactions, it is important to understand that it is the opportunity for electron-pair sharing that enables proton transfer to take place.

Take special note of the following points:. The point about the electron-pair remaining on the donor species is especially important to bear in mind. For one thing, it distinguishes a Lewis acid-base reaction from an oxidation-reduction reaction , in which a physical transfer of one or more electrons from donor to acceptor does occur. The K a expression is as follows:. Acid dissociation constants are most often associated with weak acids, or acids that do not completely dissociate in solution.

This is because strong acids are presumed to ionize completely in solution and therefore their K a values are exceedingly large. Due to the many orders of magnitude spanned by K a values, a logarithmic measure of the acid dissociation constant is more commonly used in practice.

The logarithmic constant pK a is equal to -log 10 K a. The larger the value of pK a , the smaller the extent of dissociation. A weak acid has a pK a value in the approximate range of -2 to 12 in water. Acids with a pK a value of less than about -2 are said to be strong acids. A strong acid is almost completely dissociated in aqueous solution; it is dissociated to the extent that the concentration of the undissociated acid becomes undetectable.

Acetic acid dissociation : The acetic acid partially and reversibly dissociates into acetate and hydrogen ions. What is the pK a for acetic acid? This reaction has a special equilibrium constant denoted K W , and it can be written as follows:. Here we have the reason that neutral water has a pH of 7. This relationship will always apply to aqueous solutions. It is a quick and convenient way to find pH from pOH, hydrogen ion concentration from hydroxide ion concentration, and more.

The pH and pOH Scale : Relation between p[OH] and p[H] brighter red is more acidic, which is the lower numbers for the pH scale and higher numbers for the pOH scale; brighter blue is more basic, which is the higher numbers for the pH scale and lower numbers for the pOH scale. Generically, this p-notation can be used for other scales.

However, because these values are often very small for weak acids and weak bases, the p-scale is used to simplify these numbers and make them more convenient to work with.

Quite often we will see the notation pK a or pK b , which refers to the negative logarithms of K a or K b , respectively. Interactive: pH : Test the pH of things like coffee, spit, and soap to determine whether each is acidic, basic, or neutral. Visualize the relative number of hydroxide ions and hydronium ions in solution. Switch between logarithmic and linear scales.

Investigate whether changing the volume or diluting with water affects the pH. Or you can design your own liquid! Privacy Policy. Skip to main content. Acids and Bases. Search for:. Acids and Bases Nature of Acids and Bases Acids and bases will neutralize one another to form liquid water and a salt.

Learning Objectives Describe the general properties of acids and bases, comparing the three ways to define them. Lewis Acids Lewis acids accept an electron pair. Various species can act as Lewis acids. All cations are Lewis acids since they are able to accept electrons. Molecules where the central atom can have more than 8 valence shell electrons can be electron acceptors, and thus are classified as Lewis acids e.

Molecules that have multiple bonds between two atoms of different electronegativities e. Lewis Bases Lewis Bases donate an electron pair. While lewis bases have lone pair electrons to share and thus occupy a higher energy level. This helps explain the resulting hexaaquaaluminum III ion. Amphoterism As of now you should know that acids and bases are distinguished as two separate things however some substances can be both an acid and a base.

Shunichi Fukuzumi and, Kei Ohkubo. Journal of the American Chemical Society 35 , Harwood, William S. An acid is a substance that accepts a pair of electrons, and in doing so, forms a covalent bond with the entity that supplies the electrons. Acid : Acids are those which accepts an electron-pairs.

Base : Bases are those which donates ab electron-pairs. Alkali : It is a base that dissolves in water. It is basically a base and the pH greater than 7.