Name: electron-pair reactions in acid-base chemistry
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 33 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.6.3

Lewis Acids and Bases

布朗斯特-劳里模型用质子来定义 酸和碱，其中酸是质子供体，而碱是质子受体。相反，路易斯模型用电子对来定义 酸和碱，其中 路易斯酸是 电子对受体，而 路易斯碱 是电子对供体。在布朗斯特酸中，像醋酸，氢也可以作为路易斯酸，因为它有 一个空的轨道来接受碱提供的电子，比如水，作为路易斯碱。路易斯模型的优点在于，它允许科学家 将更多的化合物归类为酸 包括 那些没有可电离质子的化合物。例如，三氟化硼不能被布朗斯特-劳里模型 归类为酸，因为它不含 氢。然而，三氟化硼有一个不完整的八位体，它有一个空轨道，可以接受 来自路易斯碱的电子对，比如氨，因此，可以作为一种路易斯酸。由这种路易斯酸碱反应形成的产物 称为路易斯酸碱加合物。有些分子，像二氧化碳，可以重新排列它们的电子以作为路易斯酸。例如，在水和二氧化碳之间的反应中，一个电子对从碳氧 π 键移动 到二氧化碳的末端氧。在碳原子上形成的空轨道使 它能够接受来自水分子的电子对，并充当路易斯酸。当水分子提供电子对时，它起到路易斯碱的作用。在进一步的重排中，质子 从水氧转移到 二氧化碳的末端氧，从而导致碳酸加合物的形成。小的金属阳离子，像 Al（III）可以重新获得电子对并充当路易斯酸。例如，Al（III）从水中接受 孤对电子，并形成六水合铝离子。在这里，水分子提供电子对 并充当路易斯碱。

路易斯酸和碱

1923 年， G. N. 路易斯提出了一个 酸-碱 行为的通用定义，其中酸和碱通过接受或捐赠一对电子并形成坐标共价键的能力来识别。 
 当键中的某个原子同时提供两个键电子时，就会出现坐标系共价键 (或配位键)。 例如，当水分子与氢离子结合形成水合氢离子时，就会出现坐标共价键。 当氨分子与氢离子结合形成铵离子时，也会产生坐标共价键。 这两个方程式都显示在此处。 
 <img alt="Image1" src="/files/ftp_upload/11407/11407_Image_1.svg" style="height: 175px;" />
 涉及形成坐标共价键的反应被归类为路易斯 酸-碱 化学。 组成键的电子对的捐赠物种是路易斯碱，接受电子对的物种是路易斯酸，反应的生成物是路易斯 酸-碱 加合物。 如上述两个例子所示， 布朗斯特-劳里 酸-碱 反应代表路易斯酸反应的一个子类别，特别是那些酸类为 H+ 的反应。 下面介绍一些涉及其他路易斯酸和碱的示例。 
 三氟硼中的硼原子 BF3 在其价壳层中只有六种电子。 由于缺乏首选的八偶体， BF3 是一种非常好的路易斯酸，并与许多路易斯碱发生反应；在这种反应中，氟化离子是路易斯碱，其中一种是孤对： 
 <img alt="Image2" src="/files/ftp_upload/11407/11407_Image_2.svg" style="height: 150px;" />
 在以下反应中，两个氨分子 (路易斯碱) 中的每一个向银离子路易斯酸捐献一对电子： 
 
 <img alt="Image3" src="/files/ftp_upload/11407/11407_Image_3.svg" style="height: 150px;" />
 非金属氧化物充当路易斯酸并与氧化物离子路易斯碱发生反应以形成氧化阴离子： 
 <img alt="Image4" src="/files/ftp_upload/11407/11407_Image_4.svg" style="height: 150px;" />
 许多路易斯 酸-碱 反应是位移反应，其中一个路易斯碱从 酸-碱 加合物中置换另一个路易斯碱，或者一个路易斯酸置换另一个路易斯酸： 
 <img alt="Image5" src="/files/ftp_upload/11407/11407_Image_5.svg" style="height: 350px;" />
 另一种类型的路易斯 酸-碱 化学涉及形成一个错合离子 (或一个协调组合体) ，其中包括一个中心原子，通常是一个过渡金属阳离子，周围有被称为配体的离子或分子。 这些配体可以是中性分子 (如 H2O 或 NH3) ，也可以是离子 (如 CN 或 OH)。 通常，配体充当路易斯碱，向中心原子捐献一对电子。 
 本文改编自<a href="https://openstax.org/books/chemistry-2e/pages/15-2-lewis-acids-and-bases"> Openstax, 化学 2e, 第15.2节：路易斯酸和碱</a>。

1923年，G. N. Lewis 提出了一种酸碱行为的广义定义，其中酸和碱根据其接受或提供电子对的能力来识别。

Education

教育

JoVE Core

化学

Acids and Bases

酸与碱

KEY TERMS AND CONCEPTS

关键术语与概念

electron-pair reactions in acid-base chemistry

Electron-pair reactions explain Lewis acid-base chemistry. In 1923, G. N. Lewis described acids and bases by how they accept or donate a pair of electrons. When that electron pair forms a coordinate covalent bond, one atom supplies both bonding electrons. This bond is also called a dative bond.

A simple example is the reaction of water with a hydrogen ion to make a hydronium ion. Ammonia can also combine with a hydrogen ion to form an ammonium ion. In both cases, the reaction creates a Lewis acid-base adduct. The electron-pair donor is the Lewis base, and the electron-pair acceptor is the Lewis acid.

Brønsted-Lowry acid-base reactions fit inside Lewis acid chemistry. In those reactions, the acid species is H+. Other Lewis acids show the same electron-pair pattern in different ways. Boron trifluoride, BF3, is a strong Lewis acid because boron has only six electrons in its valence shell and still needs an octet. A fluoride ion can donate a lone pair to BF3 and form an adduct.

Lewis acids can also bind more than one base. In one example, two ammonia molecules each donate a pair of electrons to a silver ion, which acts as the Lewis acid. Nonmetal oxides also behave as Lewis acids and react with oxide ions, which are Lewis bases, to form oxyanions. Many Lewis acid-base reactions are displacement reactions. In these reactions, one Lewis base can replace another base in an adduct, or one Lewis acid can replace another acid.

Lewis acid-base chemistry also helps form complex ions, or coordination complexes. These complexes have a central atom, often a transition metal cation, surrounded by ligands. Ligands can be neutral molecules such as H2O or NH3, or ions such as CN- or OH-. In many cases, the ligands act as Lewis bases and donate electron pairs to the central atom.

Electron-Pair Reactions in Acid-Base Chemistry

electron-pair-reactions-in-acid-base-chemistry

bronsted-lowry acids and bases

Proton Transfer in Acids and Bases

Acids and bases can be understood through proton transfer. Early scientists described acids by their sour taste, their effect on dyes, and their reaction with limestone, which releases carbon dioxide. Robert Boyle also noted that acid solutions can lose these properties after contact with alkali, or base, solutions. The modern view developed step by step. Humphry Davy showed that hydrogen is the essential part of acids. Joseph Louis Gay-Lussac then described acids as substances that neutralize...

water: a bronsted-lowry acid and base

Water as an Amphiprotic Substance

Water can act as both a Brønsted-Lowry acid and a Brønsted-Lowry base. When hydrogen fluoride dissolves in water, it donates protons to water. This is acid ionization. The products are hydronium ions and fluoride ions. Water can also accept protons from another substance. When pyridine dissolves in water, it accepts a proton from water molecules. This is base ionization. The products are hydroxide ions and pyridinium ions. These reactions show that water can play either role. A substance that...

ph scale

pH and pOH in Water

pH and pOH show how hydronium and hydroxide ions behave in water and other aqueous solutions. These ion concentrations are linked by the ion product of water, K w , so when one goes up, the other goes down. Because ion concentrations can differ by huge amounts, a logarithmic scale is used to describe them. pH is defined from the hydronium ion concentration, [H3O+], and pOH is the matching p-function for hydroxide ion concentration. These two values are also connected through the K w...

relative strengths of conjugate acid-base pairs

relative-strengths-of-conjugate-acid-base-pairs

How Ka and Kb Show Acid-Base Strength

Brønsted-Lowry acid-base chemistry is based on proton transfer. That idea helps show how the strength of an acid is linked to the strength of its conjugate base, and vice versa. Acid and base strength is measured with ionization constants, Ka and Kb, which tell how far an ionization reaction goes. For the conjugate pair HA and A−, the acid ionizes in water and the base reaction can be written for the partner species. When the two reactions are added, they give the autoionization of water. The...

strong acid and base solutions

Strong Acids, Strong Bases, and pH

Strong acids and strong bases change the pH of a solution by dissociating completely in water. A strong acid produces hydronium ions, which are H3O+ ions, and a strong base produces hydroxide ions, OH-. Because the dissociation is complete, the ion concentration can be found from the starting concentration and the molar ratio. For example, 0.20 M hydrobromic acid dissociates fully in water. It produces 0.20 M hydronium ions and 0.20 M bromide ions. A 0.015 M KOH solution also dissociates...

weak acid solutions

Weak Acid Equilibrium in Water

Weak acid equilibrium in water explains why many acids only partially react when dissolved. Most weak acid molecules stay in their original form, and only a small amount of hydronium ions forms. Weak acids are common in nature. They help create the tangy taste of citrus fruits, the stinging sensation from insect bites, and the smells linked to body odor. Acetic acid is a familiar weak acid. It is the main ingredient in vinegar. Its equation uses a double arrow to show that the reaction with...

weak base solutions

Weak Base pH and Kb Calculations

Weak base pH and Kb calculations show how partially reacting bases change water chemistry. Weak bases produce hydroxide ions when they dissolve by reacting with water molecules. Because the reaction only happens partly, these compounds are classified as weak bases. Weak bases are common in nature and in technology. Ammonia is one major example. Global production of ammonia is typically well over 100 metric tons each year. It is used as an agricultural fertilizer, a starting material for...

mixtures of acids

pH of Acid Mixtures

The pH of acid mixtures depends on the acids present, their dissociation constants, and their starting concentrations. When a solution contains two different acids, the pH can be found by choosing the method that fits their relative strengths. This makes acid mixtures a useful case for applying acid-base rules in chemistry. In a mixture of a strong acid and a weak acid, the strong acid dissociates completely and supplies almost all of the hydronium ions in the solution. The weak acid...

ions as acids and bases

Salt Hydrolysis and pH of Solutions

Salt hydrolysis explains why some salt solutions are acidic, basic, or neutral. Salts are ionic compounds made of cations and anions. In water, either ion may react with water through an acid or base ionization reaction. The pH of the solution depends on the relative acid-base strength of the ions in the salt. Ammonium chloride is a good example of an acidic salt. When it dissolves, it separates into ammonium ions and chloride ions. The ammonium ion is the conjugate acid of ammonia, so it can...

determining the ph of salt solutions

Salt Hydrolysis and pH in Solutions

Salt hydrolysis and pH in solutions depend on the ions released when a salt dissolves. Some ions react with water, while others do not. The balance between the cation and anion helps show whether the solution becomes acidic, basic, or neutral. Salts with pH-neutral anions and cations that produce hydronium ions give acidic solutions with pH below 7. Ammonium nitrate is one example. In NH4NO3, NO3− does not react with water, but NH4+ forms hydronium ions, so the solution is acidic. Other salts...

acid/base strengths and dissociation constants

acidbase-strengths-and-dissociation-constants

Acid and Base Strength in Water

Acid and base strength in water depends on how much a substance ionizes after it dissolves. If ionization is nearly complete, the substance is called strong. If only a small amount ionizes, it is called weak. Weak acids and weak bases are much more common than strong ones. The most common strong acids are HClO4, HCl, HBr, HI, HNO3, and H2SO4. The most common strong bases are LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. These strong acids and bases ionize essentially completely in water. <br...

polyprotic acids

Stepwise Ionization of Polyprotic Acids

Polyprotic acids lose hydrogen ions in steps. The number of ionizable protons in a molecule determines whether an acid is monoprotic, diprotic, or triprotic. This video also shows that polyprotic bases can accept more than one proton. Monoprotic acids have one ionizable hydrogen atom per molecule. Examples include HCl, HNO3, and HCN. Their reactions with water form hydronium ions and the matching anion. Acetic acid, CH3CO2H, is also monoprotic because only the hydrogen in the carboxyl group...

acid strength and molecular structure

How Bonding Affects Acid Strength

Acid strength depends on bonding, electronegativity, and oxidation number. These factors help explain why some hydrogen compounds act as strong acids, while others behave as weak acids or bases. For binary acids, which are hydrogen compounds with one other nonmetal, acidity increases as the H-A bond gets weaker down a group. That is why the order for group 17 is HF &lt; HCl &lt; HBr &lt; HI, and for group 16 it is H2O &lt; H2S &lt; H2Se &lt; H2Te. Across a period, acid strength increases as...

lewis acids and bases

Electron-pair reactions explain Lewis acid-base chemistry. In 1923, G. N. Lewis described acids and bases by how they accept or donate a pair of electrons. When that electron pair forms a coordinate covalent bond, one atom supplies both bonding electrons. This bond is also called a dative bond. A simple example is the reaction of water with a hydrogen ion to make a hydronium ion. Ammonia can also combine with a hydrogen ion to form an ammonium ion. In both cases, the reaction creates a Lewis...

key terms and concepts

Learn how Lewis acids and bases use electron pairs to form coordinate covalent bonds, adducts, complex ions, and examples like BF3, Ag+, and hydronium.

Electron-Pair Reactions in Acid-Base Chemistry | JoVE K12

chemistry

JoVE Core 化学通过简单明了且通俗易懂的动画视频课程，将普通化学概念带入到现实生活当中。此外，在科学家行动视频中，我们演示了在实验室中进行的经典和原始研究实验。

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Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Tennessee Academic Standards

High School

Matter and Its Interactions

CHEM1.PS1.8

Texas Essential Knowledge and Skills

CHEM.12

CHEM.12.D

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9-12.PS.3.6.c

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New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-11.

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Electron-Pair Reactions in Acid-Base Chemistry

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