Name: electron-pair reactions in acid-base chemistry
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 33 s
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Lewis Acids and Bases

Het Brønsted-Lowry-model definieert zuren en basen in termen van protonen, waarbij zuren protondonoren zijn en basen protonacceptoren. Daarentegen definieert het Lewis-model zuren en basen in termen van elektronenparen, waarbij Lewiszuren elektronenpaaracceptoren zijn en Lewisbasen elektronenpaardonoren. In een Brønstedzuur, zoals azijnzuur, kan de waterstof ook als een Lewiszuur werken, omdat het een lege orbitaal heeft om elektronen te accepteren die zijn afgestaan vanaf een base, zoals water, die als een Lewisbase fungeren.Het voordeel van het Lewis-model is dat het wetenschappers in staat stelt om een groter aantal verbindingen als zuren te classificeren, inclusief degene die geen ioniseerbare protonen hebben. Boortrifluoride kan bijvoorbeeld niet als een zuur worden geclassificeerd door het Brønsted-Lowry-model omdat het geen waterstof bevat. Boortrifluoride bezit echter een onvolledig octet met een lege orbitaal dat een elektronenpaar kan accepteren van een Lewisbase, zoals ammoniak, en daarom kan werken als een Lewiszuur.Het resulterende product gevormd door dergelijke Lewiszuur-base-reacties wordt een Lewiszuur-base-adduct genoemd. Sommige moleculen, zoals kooldioxide, kunnen hun elektronen herschikken om als een Lewiszuur te werken. Bijvoorbeeld, in de reactie tussen water en kooldioxide, beweegt een elektronenpaar van de koolstof-zuurstof pi-binding naar de terminale zuurstof van het kooldioxide.De resulterende lege orbitaal op het koolstofatoom stelt het in staat om het elektronenpaar van een watermolecuul te accepteren en als een Lewiszuur te werken. Omdat het watermolecuul het elektronenpaar doneert, fungeert het als een Lewisbase. Bij verdere herrangschikking wordt een proton overgebracht van de waterzuurstof naar de terminale zuurstof van het kooldioxide, wat resulteert in de vorming van het koolzuuradduct.Kleine metaalkationen, zoals Al(III)kunnen opnieuw elektronenparen verkrijgen en als Lewiszuren werken. Al(III)accepteert bijvoorbeeld vrije elektronenparen uit water en vormt hexaaqua-aluminiumionen. Hier doneren watermoleculen elektronenparen en fungeren ze als een Lewisbase.

lewis-zuren en basen

In 1923 stelde GN Lewis een algemene definitie voor van zuur-base-gedrag, waarbij zuren en basen worden geïdentificeerd aan de hand van hun vermogen om een paar elektronen te accepteren of te doneren en een gecoördineerde covalente binding te vormen. Een gecoördineerde covalente binding (of datieve binding) treedt op wanneer een van de atomen in de binding beide bindende elektronen levert. Een gecoördineerde covalente binding treedt bijvoorbeeld op wanneer een watermolecuul zich combineert met een waterstofion om een hydroniumion te vormen. Een gecoördineerde covalente binding ontstaat ook wanneer een ammoniakmolecuul zich combineert met een waterstofion om een ammoniumion te vormen. Beide vergelijkingen worden hier weergegeven. <img alt="Image1" src="/files/ftp_upload/11407/11407_Image_1.svg" style="height: 175px;"> Reacties waarbij sprake is van de vorming van gecoördineerde covalente bindingen worden geclassificeerd als Lewis-zuur-base-chemie. De soort die het elektronenpaar doneert dat de binding vormt, is een Lewis-base, de soort die het elektronenpaar accepteert is een Lewis-zuur en het product van de reactie is een Lewis-zuur-base-adduct. Zoals de twee voorbeelden hierboven illustreren, vertegenwoordigen de zuur-base-reacties van Brønsted-Lowry een subcategorie van Lewis-zuurreacties, met name die waarbij de zuursoort H+ is. Hieronder worden enkele voorbeelden beschreven waarbij andere Lewis-zuren en -basen betrokken zijn. Het booratoom in boortrifluoride, BF3, heeft slechts zes elektronen in zijn valentieschil. Omdat BF3 niet het voorkeursoctet heeft, is het een zeer goed Lewis-zuur en reageert het met veel Lewis-basen; een fluoride-ion is de Lewis-base in deze reactie en doneert een van zijn enige paren: <img alt="Image2" src="/files/ftp_upload/11407/11407_Image_2.svg" style="height: 150px;"> In de volgende reactie doneert elk van de twee ammoniakmoleculen, Lewis-basen, een paar elektronen aan een zilverion, het Lewis-zuur: <img alt="Image3" src="/files/ftp_upload/11407/11407_Image_3.svg" style="height: 150px;"> Niet-metaaloxiden fungeren als Lewis-zuren en reageren met oxide-ionen, Lewis-basen, om oxyanionen te vormen: <img alt="Image4" src="/files/ftp_upload/11407/11407_Image_4.svg" style="height: 150px;"> Veel Lewis-zuur-base-reacties zijn verdringingsreacties waarbij de ene Lewis-base een andere Lewis-base verdringt uit een zuur-base-adduct, of waarbij het ene Lewis-zuur een ander Lewis-zuur verdringt: <img alt="Image5" src="/files/ftp_upload/11407/11407_Image_5.svg" style="height: 350px;"> Een ander type Lewis-zuur-base-chemie omvat de vorming van een complex ion (of een coördinatiecomplex) dat een centraal atoom omvat, meestal een overgangsmetaalkation, omgeven door ionen of moleculen die liganden worden genoemd. Deze liganden kunnen neutrale moleculen zijn, zoals H2O of NH3, of ionen, zoals CN– of OH–. Vaak fungeren de liganden als Lewis-basen en doneren ze een paar elektronen aan het centrale atoom.

Lewis-zuren en basen

In 1923, G. N. Lewis proposed a generalized definition of acid-base behavior in which acids and bases are identified by their ability to accept or to ...

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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

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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

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Electron-Pair Reactions in Acid-Base Chemistry

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