Molecular Structures of Acids and Bases

8 Key excerpts on "Molecular Structures of Acids and Bases"

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  Chemistry

  The Molecular Nature of Matter

  • Neil D. Jespersen, Alison Hyslop(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  • compare the strengths of Brønsted–Lowry acids and bases, how they are classified as strong or weak, and the strengths of conjugate acid–base pairs. • using the periodic table, describe the trends in the strengths of binary acids and oxoacids. • define Lewis acids and bases and compare them to the Arrhenius and Brønsted–Lowry definitions. • using the periodic table, describe which elements are most likely to form acids or bases. • describe how the production of advanced ceramics depends on acid–base chemistry, including the sol-gel process. Acids and Bases: A Molecular Look CHAPTER 15 Yuri Smityuk / Getty Images 760 CHAPTER 15 Acids and Bases: A Molecular Look FIGURE 15.1 The reaction of gaseous HCl with gaseous NH 3 . As each gas escapes from its concentrated aqueous solution and mingles with the other, a cloud of microcrystals of NH 4 Cl forms above the bottles. 1 When the single electron is removed from a hydrogen atom, what remains is just the nucleus of the atom, which is a proton. Therefore, a hydrogen ion, H + , consists of a proton, and the terms proton and hydrogen ion are often used interchangeably. Andy Washnik CONNECTING TO THE LEARNING OBJECTIVES From the beginning of this book, we have been suggesting that you outline the chapter that you are studying and that you work through the questions in the back of the chapter to practice solving chemistry problems. We have also suggested that you use a notebook dedicated to chemistry to keep your notes. Here are a few additional suggestions to help you learn the material in this chapter. 1. Take notes in class and when you read the chapter. Notes are messy, full of questions, have diagrams and pictures, include your reactions to the material, and draw connections between concepts. Sometimes they even include doodles. 2. Choose two concepts from the chapter and prepare a lesson to teach the material to someone else.

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  Chemistry

  With Inorganic Qualitative Analysis

  • Therald Moeller(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  17

  ACIDS AND BASES

  Publisher Summary

  This chapter discusses two major methods of defining acids and bases, the Bronsted-Lowry system, based on proton donation; and the Lewis system, based on electron-pair donation. It describes the behavior of acids and bases in aqueous systems. The chapter explains the structural factors that influence the strengths of the acids and bases. A solvent system acid is any substance that gives the cation of the solvent; a solvent system base is any substance that gives the anion of the solvent. The chapter illustrates the inter-relationships among conjugate acid-base pairs. Amphiprotism is the ability of a substance to either gain or lose a proton. The strength of a base depends upon how easily a compound will give up an OH– ion or how strongly it will attract a proton. Electronegativity is the ability of an atom in a bond to attract electrons. The ionic character of a bond increases with the increasing electronegativity of the nonmetal atom. The exact concentration of an acid or base in solution can be determined experimentally by titration. The strength of a protonic acid in aqueous solution is measured by the extent to which the equilibrium proceeds in the direction of ion formation.

  In this chapter two major methods of defining acids and bases are introduced—the Br0nsted–Lowry system, based on proton donation; and the Lewis system, based on electronpair donation. The behavior of acids and bases in aqueous systems is discussed in detail. Structural factors that influence the strengths of these acids and bases are examined, as are equilibria in aqueous solutions of acids and bases.

  Y ou should learn a few practical things about acids and bases, if you have not already experienced them . (

  How Ira Remsen, founder of the chemistry department at Johns Hopkins University, discovered the properties of nitric acid in the 1800s is described in the Thoughts on Chemistry at the end of this chapter

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  Chemistry

  The Molecular Nature of Matter

  • James E. Brady, Neil D. Jespersen, Alison Hyslop(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  But there are no protons being transferred, so our definitions require further generalizations. These were provided by G. N. Lewis, after whom Lewis symbols are named. Lewis Definitions of Acids and Bases 1. A Lewis acid is any ionic or molecular species that can accept a pair of electrons in the formation of a coordinate covalent bond. 2. A Lewis base is any ionic or molecular species that can donate a pair of electrons in the formation of a coordinate covalent bond. 3. Neutralization is the formation of a coordinate covalent bond between the donor (base) and the acceptor (acid). Practice Exercise 15.15 Practice Exercise 15.16 Lewis acid–base definitions 15.4 | Lewis Acids and Bases 747 Examples of Lewis Acid–Base Reactions The reaction between BF 3 and NH 3 illustrates a Lewis acid–base neutralization. The reaction is exothermic because a bond is formed between N and B, with the nitrogen donating an electron pair and the boron accepting it. New coordinate covalent bond Lewis base Lewis acid H 9 N B 9 F + H H F F H 9 N B 9 F H H F F NH 3 BF 3 NH 3 BF 3 Note that as the bond forms from ammonia to boron trifluoride, the geometry around the boron changes from planar triangular to tetrahedral, which is what is expected with four bonds to the boron. The ammonia molecule thus acts as a Lewis base. The boron atom in BF 3 , having only six electrons in its valence shell and needing two more to achieve an octet, accepts the pair of electrons from the ammonia molecule. Hence, BF 3 is functioning as a Lewis acid. As this example illustrates, Lewis bases are substances that have completed valence shells and unshared pairs of electrons (e.g., NH 3 , H 2 O, and O 2- ). A Lewis acid, on the other hand, can be a substance with an incomplete valence shell, such as BF 3 or H + . A substance can also be a Lewis acid even when it has a central atom with a complete valence shell.

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  Basic Physical Chemistry for the Atmospheric Sciences

  • Peter V. Hobbs(Author)
  • 2000(Publication Date)
  • Cambridge University Press

    (Publisher)

  5 Acids and bases Very early in the history of chemistry many substances were designated as acids, bases, and salts. Acids have a sour taste (e.g., citric acid gives lemon juice its sour taste); they dissolve certain metals; and they also dissolve carbonate minerals to produce carbon dioxide. Bases have a bitter taste (e.g., sodium carbonate); they feel slippery when touched; and they react with many dissolved metal salts to form precipitates. However, the most striking characteristic of bases is their ability to neutralize the properties of acids; when a base reacts with an acid a salt is produced. The French chemist Lavoisier thought that all acids contain oxygen (the word oxygen means acid former in Greek). However, it was sub-sequently found that many acids contain no oxygen (e.g., hydrochloric acid, HC1), but that they all contain hydrogen. Acids and bases figure prominently in the equilibrium of aqueous solu-tions, where they significantly enhance the electrical conductivity of water. In this chapter, we will explore some of the important properties of acids and bases in aqueous solutions. This will lead us to a discussion of several theories of acids and bases. 5.1 Some definitions and concepts Equation (4.22) is valid for aqueous solutions as well as for pure water. A solution for which [H + (aq)] = [OH~(aq)] is said to be neutral; thus, pure water is neutral. If [H + (aq)] > [OH~(aq)] the solution is said to be acidic. If [OH(aq)] > [H + (aq)] the solution is said to be basic. Exercise 5.1. If 0.02 mole of hydrochloric acid is dissolved in 1L 1 of water, what are the concentrations of H + (aq) and OH(aq) ions I in the solution at 25°C? I 83 84 Acids and bases Solution. Hydrochloric acid is a gas under normal conditions, but it is a strong electrolyte that dissolves in water to form equal numbers of H + (aq) and Q(aq).

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  Inorganic Chemistry for Geochemistry and Environmental Sciences

  Fundamentals and Applications

  • George W. Luther, III(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  Chapter 7 Acids and Bases 7.1 Introduction Acids and bases have been known since before Roman times, for their ability to transform a chemical substance into other chemical forms. For example, sulfuric acid (, oil of vitriol; vitriolic acid) could be produced by the aqueous oxidation of pyrite, which is a common mineral used for many purposes [1]. dehydrates sugar as well as metal hydrates with sometimes dramatic color changes, and also dissolves metals via redox reactions. It is normally the chemical that is produced and sold in greatest quantity in the world each year. The first base was called lye, which was obtained by leaching ashes with water producing potassium hydroxide solution. Lye is a common name for bases, which are used in a variety of purposes including wood degradation into paper or fibers and soap production. 7.2 Arrhenius and Bronsted–Lowry Definitions Common acids such as hydrochloric acid (HCl) and nitric acid were not formally prepared until about the 16th century, so formal definitions of acids and bases similar to bonding theories are relatively new. In 1884, Svante Arrhenius defined an acid as a chemical species that when dissolved in water produced the hydrogen ion,. Although useful, the definition is limited as it does not encompass a large variety of reactions and only considers water as solvent. In 1923, Brønsted and Lowry defined an acid and base reaction as one that involves a hydrogen ion transfer between two reactants. The acid is the hydrogen ion donor (the Brønsted acid) and the base is the hydrogen ion acceptor (the Brønsted base). This definition applies to all solvents and the gas phase. For example, the reaction between HCl and can occur in water as solvent or in the gas phase (an atmospheric reaction) and results in complete transfer to form the hydronium ion,

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  Essentials of Organic Chemistry

  For Students of Pharmacy, Medicinal Chemistry and Biological Chemistry

  • Paul M. Dewick(Author)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  4

  Acids and bases

  4.1 Acid–base equilibria

  A particularly important concept in chemistry is that associated with proton loss and gain, i.e. acidity and basicity. Acids produce positively charged hydrogen ions H+ (protons) in aqueous solution; the more acidic a compound is, the greater the concentration of protons it produces. In water, protons do not have an independent existence, but become strongly attached to a water molecule to give the stable hydronium ion H3 O+ . In the Brønsted–Lowry definition:

  • an acid is a substance that will donate a proton;
  • a base is a substance that will accept a proton.

  Thus, in water, the acid HCl ionizes to produce H3 O+ and Cl− ions.

  H3 O+ is termed the conjugate acid (of the base H2 O) and Cl− is termed the conjugate base

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  Organic Chemistry Concepts and Applications for Medicinal Chemistry

  • Joseph E. Rice(Author)
  • 2014(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 4

  Acids and Bases∗

  Abstract

  This chapter provides a review of the concept of acids and bases. Since drugs work mainly within an aqueous environment in the body, the largest part of this chapter is concerned with acid–base properties in water. Factors that affect the equilibrium between an acid and its conjugate base, or a base and its conjugate acid, are discussed. The concept of salts as products of acid–base reactions is then introduced. Using a generalized acid, the Henderson–Hasselbalch equation is derived and its use in predicting the degree to which an acid or base is ionized in an aqueous solution of known pH is explored. A method for rapidly predicting approximate acid–base strength for a wide range of functional groups is then presented, making use of a device known as the pK a –pK b calculator. The final section serves as a brief introduction to the concept of Lewis acids and bases.

  Keywords

  Acid ; Base ; Equilibrium ; Henderson–Hasselbalch equation ; Ionization ; Lewis acid ; Lewis base ; Neutral ; Salt

  Drug molecules find themselves in an aqueous environment once they enter the body. Depending on the nature of whatever functional groups the drug possesses, it will generally behave as either an acid or a base and will exist to a certain extent as a charged species. The degree to which this occurs will play a role in determining how that drug gets distributed throughout the body. Thus an understanding of the concepts of acids and bases is a critical aspect of medicinal chemistry. The definition of the terms acid and base however depends upon which of the two theories (Brønsted–Lowry or Lewis ) is most applicable to the situation at hand. When dealing with aqueous solutions, the Brønsted–Lowry theory is most commonly invoked, although Lewis acidity and basicity is still important. In this chapter, we will focus first on the Brønsted–Lowry theory in which an acid is defined as a group that can donate a proton (a hydrogen cation) and a base

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  Fundamentals of Molecular Structural Biology

  • Subrata Pal(Author)
  • 2019(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 4

  Chemical basis of biology

  Abstract

  The present chapter deliberates on the physical forces and factors based on which atoms form molecular structures and the molecules interact among themselves. Atoms are held together in a molecule by chemical bonds and the electron configuration of an atom is crucial for its participation in a bond. Bonding theories—Lewis octet, valence bond, and molecular orbital—have been introduced. Noncovalent interactions which are important for molecular three-dimensional structure and intermolecular binding have been discussed. The spontaneity of a molecular process has been related to the Gibbs free energy function. The kinetics of chemical reactions have been explained based on the Arrhenius equation, collision theory, transition state theory and quantum tunneling.

  Keywords

  Atom; Molecule; Chemical bond; Octet rule; Atomic orbital; Molecular orbital; Noncovalent interaction; Gibbs free energy; Chemical kinetics

  Molecular structural biology is all about understanding and explaining biological processes in the language of molecular structures and interactions. In the previous chapter, we have looked at the structure of the atom from classical and quantum mechanical perspectives. In this chapter, we shall deliberate on the physical forces and factors based on which atoms form molecular structures and the molecules interact among themselves.

  4.1 From atoms to molecules

  Molecules are formed when x number of atoms (x  = 2, 3, 4,…) are held together by what are known as chemical bonds . All x may not be the same type of atoms. The obvious question then would be why and how the bonds are formed.

  4.1.1 Electron configuration of atoms

  We know that atoms consist of positively charged protons in the nucleus (leaving aside the uncharged neutrons) and negatively charged electrons in the orbitals. When two atoms approach each other, a complex set of electrostatic interactions develop among the charged particles. The electrons of one atom are attracted by the nucleus, but repelled by the electrons of the other atom and vice versa. At the same time, the two nuclei also repel each other. If these interactions result in the reduction in energy of each atom and, thus, the total system, a chemical bond is formed. Therefore, the interactions should be understood in terms of the electron configurations of the atoms.

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