Br0nsted-Lowry definition of acids and bases

Although the concepts of specific acid and specific base catalysis were useful in the analysis of some early kinetic data, it soon became apparent that any species that could effect a proton transfer with the substrate could exert a catalytic influence on the reaction rate. Consequently, it became desirable to employ the more general Br0nsted-Lowry definition of acids and bases and to write the reaction rate constant as... 

This is a very useful relationship. You should practice writing equations according to the Br0nsted-Lowry definitions of acids and bases and familiarize yourself with Table 1.7 which gives the pXa s of various Brpn-sted acids. 

The Br0nsted-Lowry definition of acids and bases depends on the transfer of a proton from the acid to the base. The base uses a pair of nonbonding electrons to form a bond to the proton. G. N. Lewis reasoned that this kind of reaction does not need a proton. Instead, a base could use its lone pair of electrons to bond to some other electron-deficient atom. In effect, we can look at an acid-base reaction from the viewpoint of the bonds that are formed and broken rather than a proton that is transferred. The following reaction shows the proton transfer, with emphasis on the bonds being broken and formed. Organic chemists routinely use curved arrows to show the movement of the participating electrons. 

The Br0nsted-Lowry definition of acids and bases does not replace the Arrhenius definition, but extends it. The Bronsted-Lowry definition of acids and bases requires you to take a closer look at the reactants and products of an acid-base reaction. In this case, acids and bases are not easily defined as having hydronium and hydroxide ions. Instead, you are asked to look and see which substance has lost a proton and which has gained the very same proton that was lost. 

The Br0nsted-Lowry definitions of acids and bases are widely used in organic chemistry. As noted in the preceding equation, the conjugate acid of a substance is formed when it accepts a proton from a suitable donor. Conversely, the proton donor is converted to its conjugate base. A conjugate acid-base pair always differ by a single proton. 

Arrhenius/Br0nsted-Lowry Definitions of Acids and Bases... 

The Br0nsted-Lowry definition of acids and bases broadened the definition of acids and bases. Acids are proton donors and bases are proton acceptors. This is in agreement with Arrhenius theory but includes reactions such as that between ammonia and hydrogen chloride gases ... 

To avoid confusion between the Lewis and the Br0nsted-Lowry definitions of acids and bases, Lewis bases are sometimes called nucleophiles, and Lewis acids are called electrophiles. In the example above, water acts as a nucleophile (donates electrons), and the carbocation acts as an electrophile (receives electrons). 

Before continuing on to the last definition of acids and bases, it will be helpful to consider the definitions for strong and weak acids within the context of the Br0nsted-Lowry model of acids and bases. The definitions are really an extension of the Arrhenius ideas. In the Arrhenius definitions, strong acids and bases were those that ionize completely. Most Brpnsted-Lo wry acids and bases do not completely ionize in solution, so the strengths are determined based on the degree of ionization in solution. For example, acetic acid, found in vinegar, is a weak acid that is only about 1 % ionized in solution. That means that when acetic acid, 11C, 11,(),. is placed in water, the reaction looks like... 

The Lewis definitions of acids and bases provide for a more general view of acid-base reactions than either the Arrhenius or Br0nsted-Lowry pic ture A Lewis acid is an electron pair acceptor A Lewis base is an electron pair donor The Lewis approach incorporates the Br0nsted-Lowry approach as a subcategory m which the atom that accepts the electron pair m the Lewis acid is a proton... 

The Br0nsted-Lowry theory expands the definition of acids and bases to allow us to explain n ch more ol solution chemistry. For example, the Brpnsted-Lowry theory allows us to explain why a solution af ammonium nitrate tests acidic and a solution of potassium acetate tests basic. Most of the substances that we cofcider acids in the Arrhenius theory are also acids in the Brpnsted-Lowry theory, and the same is true of bases. Injboth theories, strong acids are those that react completely with water to form ions. Weak acids ionize only slightly. We can now explain this partial ionization as an equilibrium reaction of the weak acid, the ions, and the w ater. A similar statement can be made about weak bases ... 

The Lewis definition of acids and bases is more general than the Br0nsted-Lowry definition. 

The Br0nsted-Lowry definition of acidity discussed in the previous four sections encompasses all compounds containing hydrogen. Of even more use, however, is the Lewis definition of acids and bases, which is not limited to compounds that gain or lose protons. A Lewis acid is a substance that accepts an electron pair, and a Lewis base is a substance that donates an... 

Use the Lewis definition of acids and bases to explain the example. given for the Br0nsted-Lowry, Lux-Flood, and. solvent system definitions (Eqs. 9.1-9.4, 9.5-9.8. 9.9-9.36). 

The definitions of acid and base that we use now were provided by Brpnsted and Lowry in 1923. In the Br0nsted-Lowry definitions, an acid is a species that donates a proton, and a base is a species that accepts a proton. (Remember that positively charged hydrogen ions are also called protons.) In the following reaction, hydrogen chloride (HCl) meets the Brpnsted-Lowry definition of an acid because it donates a proton to water. Water meets the definition of a base because it accepts a proton from HCl. Water can accept a proton because it has two lone pairs. Either lone pair can form a covalent bond with a proton. In the reverse reaction, H3O is an acid because it donates a proton to CF, and CF is a base because it accepts a proton from H30. ... 

Br0nsted and Lowry proposed definitions of acids and bases in terms of their ability to transfer protons ... 

The Lewis definitions of acids and bases provide for a more general view of acid-base reactions than either the Arrhenius or Br0nsted-Lowry picture. 

A more general definition of acids and bases given by Br0nsted and Lowry is that an acid is a proton donor and a base is a proton acceptor. This definition includes the one already stated. For example, HCl is an acid because it donates a proton to H2O to form H30 ... 

In 1923, J. N. Br0nsted in Denmark and T. M. Lowry in Great Britain expanded the definition of acids and bases to inclnde bases that do not contain OH ions. A Br0nsted-Lowry acid can donate a hydrogen ion, H, to another substance, and a Br0nsted-Lowry base can accept a hydrogen ion. 

There are several definitions of acids and bases. We are especially interested here in the Br0nsted-Lowry definition and its consequences. After reviewing definitions, we shall study the strength concept of acids and bases. It is important because it allows us to predict acid-base reactions. 

What are the main characteristics of the molecules and ions that exhibit acid and base behavior In this chapter, we examine three different definitions the Arrhenius definition, the Br0nsted-Lowry definition, and the Lewis definition. Why three definitions, and which one is correct As Huheey noted in the quotation that opens this chapter, no single definition is correct. Rather, each definition is useful in a given instance. We discuss the Lewis definition of acids and bases in Section 15.11 here we discuss the other two. 

We began our definitions of acids and bases with the Arrhenius model. We then saw how the Br0nsted-Lowry model, by introducing the concept of a proton donor and proton acceptor, expanded the range of substances that we consider acids and bases. We now introduce a third model, which further broadens the range of substances that we can consider acids. This third model is the Lewis model, named after G. N. Lewis, the American chemist who devised the electron-dot representation of chemical bonding (Section 9.1). While the Br0nsted-Lowry model focuses on the transfer of a proton, the Lewis model focuses on the transfer of an electron pair. Consider the simple acid-base reaction between the ion and NH3, shown here with Lewis structures ... 

According to the Br0nsted-Lowry model, the ammonia accepts a proton, thus acting as a base. According to the Lewis model, the ammonia acts as a base by donating an electron pair. The general definitions of acids and bases according to the Lewis model focus on the electron pair. 

The modern one-element theory of acids and bases is usually credited to Br0nsted and Lowry. They proposed the proton theory independently in 1923. But G. N. Lewis, who set forth his electronic definitions of acids and bases in the same year, also explained the proton-donor concept as a special case of his broader theory. According to the proton theory, an acid donates a proton to a base, and a base accepts a proton from an acid. The acid and base may be either compounds or ions, as shown in the following examples ... 

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