Name: resonance forms in lewis structures
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 52 s
Channel: JoVE

K12 Standards

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

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.1

Resonance

ほとんどの分子やイオンは 独特のルイス構造を使って 表現することができます しかしある種の化合物は 同じように有効な 複数のルイス構造で 表すことができます 三酸化硫黄のルイス構造を 考えてみましょう 各酸素と中心の 硫黄原子の間の単結合は 酸素原子のオクテットを 満たしています しかし 硫黄のオクテットを 満たすためには 硫黄と酸素原子の一つとの間に 追加の結合を 形成しなければなりません 3つの酸素原子のいずれかが 硫黄と二重結合を形成できるため 3つの異なるルイス構造を とることができます これらの複数のルイス構造は 共鳴構造と呼ばれ 骨格構造は同じままですが 電子の分布が異なります 3つの構造はすべて分子の 有効で等価な表現ですが 自然界には存在しません 実際の構造は 共鳴構造の間で 振動するのではなく 結合長で測定できる 3つのルイス構造の ハイブリッドまたは平均です 亜硫酸塩では 硫黄-酸素単結合の長さは 1.51オングストロームであり 三酸化硫黄では 硫黄-酸素結合の長さは 1.42オングストロームです このようにハイブリッド分子 において結合長は 単結合と二重結合の 中間の長さになります ハイブリッド分子では 二重結合やローンペアに 参加している電子は 複数の結合や原子に 非局在化していることが多く 特定の原子上に 静止しているわけではありません この非局在化によって 電子の ポテンシャルエネルギーが低下し 共鳴安定化と呼ばれる 安定化が起こります 共鳴はベンゼンなどの 芳香族化合物にも 見られます ベンゼンは六方晶の炭素環で 各炭素原子に 水素が1個ずつ結合しており 炭素原子間には 一重結合と二重結合が 交互に存在しています 炭素-炭素二重結合の 位置に基づいて ベンゼンは2つの 共鳴構造を持つことができます 二重結合は通常 単結合よりも短いことを 思い出してください しかし ベンゼンのすべての 炭素-炭素結合は 炭素-炭素単結合と 炭素-炭素二重結合の 中間である 等しい結合長を 持っています したがって ベンゼンは 共鳴ハイブリッドとして存在し 内部に円を持つ 六角形で表すことができます 円はベンゼンが2つの共鳴構造の 混成体であることを示しており 二重結合は特定の 2つの炭素原子に 局在することはできません

共振

亜硝酸イオン（NO2−）のルイス構造は、N-O結合とN=O結合の位置によって、実際には2つの異なる方法で描くことができます。  
 
 <img alt="Figure1" src="https://www.jovecore.com/CDNSource/lessons/1064/1064Image_1.svg" style="height: 40px;" />
 
 亜硝酸イオンに単結合と二重結合が実際にあるとすれば、2つの結合の長さは異なると考えられます。2つの原子の間の二重結合は、同じ2つの原子の間の単結合よりも短く（そして強く）なります。しかし、実験によると、NO2−の両方のN-O結合は、同じ強さと長さを持ち、他のすべての特性において同一であることが示されています。NO2−において、窒素がオクテットを持ち、両方の結合が等価であるような単一のルイス構造を書くことはできません。 
 
 その代わりに、共鳴という概念が使われています。ある分子やイオンに対して、同じ配列の原子を持つ2つ以上のルイス構造が書かれている場合、実際の電子の分布は、様々なルイス構造が示すものの平均になります。NO2−の窒素-酸素結合のそれぞれの電子の実際の分布は、二重結合と単結合の平均です。  
 
 個々のルイス構造を共鳴形式と呼びます。実際の分子の電子構造（共鳴形式の平均値）は、個々の共鳴形式の共鳴混成と呼ばれます。ルイス構造の間にある両頭矢印は、それらが共鳴形式であることを示します。 
 
 <img alt="Figure2" src="https://www.jovecore.com/CDNSource/lessons/1064/1064Image_2.svg" style="height: 40px;" />
 
 炭酸イオン、 CO32−は、共鳴の2つ目の例を提供します。  
 
 <img alt="Figure3" src="https://www.jovecore.com/CDNSource/lessons/1064/1064Image_3.svg" style="height: 80px;" />
 
 <ul>
 <li>中心原子のオクテットを完成させるには、1つの酸素原子が炭素に二重結合していなければなりません。  </li>
 <li>しかし、すべての酸素原子は等価であり、二重結合は3つの原子のうちどれか1つから形成される可能性があります。そのため、炭酸イオンには3つの共鳴形式が存在することになります。  </li>
 <li>同一の共鳴構造が3つ書けることから、炭酸イオンの実際の電子の配置は3つの構造の平均値であることがわかっています。  </li>
 <li>ここでも実験により、3つのC-O結合がすべて同じであることがわかっています。 </li>
 </ul>
 
 共鳴混成と呼ばれる分子は、どちらかの共鳴形式で記述された電子構造を持つことはないことを常に覚えておいてください。むしろ、実際の電子構造は、常にすべての共鳴形式によって示されるものの平均値です。  
 
 共鳴理論の先駆者の一人であるジョージ・ウィーランドは、共鳴形式と共鳴ハイブリッドの関係を歴史的な例えで説明しています。中世の旅人が、初めてサイを見たとき、ドラゴンとユニコーンに共通する多くの性質を持つことから、サイをドラゴンとユニコーンの混成と表現しました。サイがある時はドラゴンでもなく、ある時はユニコーンでもないように、共鳴混成はある時はどちらの共鳴形態でもないのです。 
 
 サイのように、実験的にも存在が確認されている実在のものです。共鳴形態と共通する特徴を持っていますが、共鳴形態自体は便宜的な空想のイメージです（ユニコーンやドラゴンのように）。 
 
 本書は <a href="https://openstax.org/books/chemistry-2e/pages/7-4-formal-charges-and-resonance">、 Openstax 、 Chemistry 2e 、 Section 7.4 ： Formal Charges and Resonance から引用したものです。</a>

亜硝酸アニオン(NO2−)のルイス構造は、実際には2つの異なる方法で描画でき、N-OとN = Oの位置によって区別されます...

Education

JoVE Core

化学

Chemical Bonding: Basic Concepts

化学結合：基本概念

KEY TERMS AND CONCEPTS

主要用語と概念

resonance forms in lewis structures

Resonance forms in Lewis structures help explain molecules and ions that cannot be shown correctly with just one drawing. In nitrite ion, NO2−, the Lewis structure can be drawn in two ways. The N-O and N=O bonds switch positions in the two drawings, but the atoms stay in the same arrangement.

If nitrite really had one single bond and one double bond, the two bond lengths should be different. A double bond is shorter and stronger than a single bond between the same atoms. Experiments show that both N-O bonds in NO2− have the same length, strength, and other properties. That means the real structure is not one Lewis form alone.

Resonance is the idea used when two or more Lewis structures with the same atom arrangement can be written for one species. The actual electron distribution is an average of the electrons shown in the different forms. In NO2−, each N-O bond has an average of a single bond and a double bond. The separate Lewis structures are called resonance forms, and the real structure is called a resonance hybrid.

A double-headed arrow is written between resonance forms to show this relationship. Carbonate ion, CO3 2−, is another clear example. One oxygen must form a double bond to carbon to complete the carbon octet, but any of the three oxygen atoms can make that bond. This gives three resonance forms, and experiments show that all three C-O bonds are exactly the same.

A resonance hybrid never has the electronic structure of just one resonance form. It does not switch back and forth between forms. Instead, it always exists as the average of all the resonance forms. George Wheland used a historical comparison to explain this idea. A medieval traveler who had never seen a rhinoceros described it as a hybrid of a dragon and a unicorn, but a rhino is neither one at different times. In the same way, resonance forms are useful imaginary pictures, while the resonance hybrid is the real entity shown by evidence.

Resonance Forms in Lewis Structures

types of chemical bonds

Chemical Bonding and Bond Properties

Chemical bonding explains how atoms and ions join to form molecules and compounds. American chemist Gilbert N. Lewis pioneered chemical bonding theory with the Lewis model. This model helps explain why bonds form, why some are stronger than others, and why compounds have fixed formulas like H2O instead of H4O. Ionic bonding involves ions, which are atoms or molecules with an electrical charge. A cation is a positive ion formed when a neutral atom loses one or more electrons from its valence...

the born-haber cycle

Predicting Ionic Stability with Lattice Energy

Lattice energy helps explain why ionic compounds are stable. It measures the strength of attraction between positive and negative ions in a crystal. In one common definition, lattice energy is the energy required to separate one mole of an ionic solid into gaseous ions, so it has a positive value. Another definition uses the opposite sign and describes the energy released when gaseous ions form a lattice. When checking data, it is important to confirm which convention is being used. In either...

lewis symbols and the octet rule

Valence Electrons, Lewis Symbols, and Bonding

Chemical bonds form when atoms or ions interact in ways that lower the potential energy of a molecule. Gilbert N. Lewis created a simple model to show bond formation using valence electrons, the electrons in the outer shell. In this model, electrons are shared or transferred to help atoms reach a stable electron configuration. The Lewis model helps describe two common bond types. An ionic bond forms when electrons move from a metal to a nonmetal. A covalent bond forms when two nonmetals share...

electronegativity

Electronegativity and Polar Bonds

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond. Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The...

ionic bonding and electron transfer

Ionic Compounds and Crystal Lattices

Ionic compounds form when positive and negative ions attract each other. A cation is a positive ion, and it forms when an atom loses one or more valence electrons. An anion is a negative ion, and it forms when an atom gains one or more valence electrons. Compounds made of these ions are called ionic compounds, or salts, and the force between them is an ionic bond. The properties of ionic solids help show how strong this attraction is. They usually form rigid, brittle crystals and have high...

trends in lattice energy: ion size and charge

trends-in-lattice-energy-ion-size-and-charge

Lattice Energy Patterns in Ionic Solids

Lattice energy shows how strongly ions hold an ionic solid together. It is the energy required to separate one mole of a solid into its gaseous ions. For sodium chloride, this process requires 769 kJ per mole. The opposite convention may also be used, where lattice energy is the energy released when gaseous ions form the solid. In either case, a larger magnitude means a more stable ionic compound. For ionic crystals, lattice energy follows a pattern based on charge and ion size. The...

covalent bonding and lewis structures

Shared Electrons in Covalent Molecules

Covalent molecules form when atoms share electrons instead of transferring them. This bonding usually happens between nonmetal atoms with similar tendencies to attract electrons. Because the atoms pull on the electrons in a shared way, the bond is held together by mutual attraction. Covalent compounds often have physical properties that differ from ionic compounds. The attraction between neutral molecules is weaker than the attraction between charged ions. As a result, many covalent compounds...

bond polarity, dipole moment, and percent ionic character

bond-polarity-dipole-moment-and-percent-ionic-character

How Bond Polarity Shapes Molecular Dipoles

Bond polarity depends on electronegativity, the ability of an atom to attract shared electrons. The absolute value of the electronegativity difference, or ΔEN, gives a rough guide to bond type. When the difference is very small or zero, the bond is covalent and nonpolar. When it is larger, the bond may be polar covalent or ionic. Examples show how this works in real compounds. H–H has a ΔEN of 0, so it is nonpolar. H–Cl has a ΔEN of 0.9, so it is polar covalent. Na–Cl has a ΔEN of 2.1, so it...

lewis structures of molecular compounds and polyatomic ions

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Drawing Lewis Structures with Valence Electron Counts

Drawing Lewis structures starts with counting valence electrons and building the atom arrangement step by step. Valence electrons are the outer-shell electrons that help show how atoms bond. For ions, a positive charge means one electron is removed for each plus sign, and a negative charge means one electron is added for each minus sign. The next step is to sketch the skeleton structure. The least electronegative atom usually goes in the center, while hydrogen is almost never central. Fluorine...

resonance

Resonance forms in Lewis structures help explain molecules and ions that cannot be shown correctly with just one drawing. In nitrite ion, NO2−, the Lewis structure can be drawn in two ways. The N-O and N=O bonds switch positions in the two drawings, but the atoms stay in the same arrangement. If nitrite really had one single bond and one double bond, the two bond lengths should be different. A double bond is shorter and stronger than a single bond between the same atoms. Experiments show that...

formal charges

Lewis Structures with Formal Charge

Lewis structures can sometimes show more than one reasonable arrangement for a molecule or polyatomic ion. Formal charge helps chemists choose the best Lewis structure when that happens. It is a useful way to compare possible structures in chemistry. Formal charge is the hypothetical charge an atom would have if bonding electrons were shared evenly between the atoms. It can also be found by starting with the valence electrons of the neutral atom, subtracting the nonbonding electrons, and then...

exceptions to the octet rule

Octet Rule Exceptions in Lewis Structures

Some covalent molecules do not follow the octet rule in their Lewis structures. Their central atoms can fall into three groups: odd-electron molecules, electron-deficient molecules, and hypervalent molecules. These cases show why a Lewis structure may not always give every atom eight valence electrons. Odd-electron molecules have an odd number of valence electrons, so one electron remains unpaired. Molecules with an odd number of electrons are called radicals. Nitric oxide, NO, is one example,...

bond energies and bond lengths

How Bond Energy Predicts Reaction Heat

Bond energy helps explain why molecules stay together and how much heat a reaction may release or absorb. A covalent bond is stronger when more energy is needed to separate the atoms. The energy needed to break one specific covalent bond in one mole of gaseous molecules is called bond energy, or bond dissociation energy. For a diatomic molecule, bond energy is the standard enthalpy change for an endothermic reaction that breaks that bond. The H-H bond is a common example. Its bond energy is...

bonding in metals

Electron Sea Model in Metals

Electron sea model explains how metallic bonding holds metals together. In this model, most metal atoms do not have enough valence electrons to form ionic or covalent bonds in the usual way. Their valence electrons are held loosely because metals have low electronegativity, and their ionization energy is low, so electrons are removed easily. When a metal atom loses these outer electrons, it becomes a positively charged metal ion. The freed electrons form a delocalized electron cloud around...

key terms and concepts

Learn how resonance forms explain equal bond lengths in nitrite and carbonate ions, and how a resonance hybrid represents the real electron distribution.

Resonance Forms in Lewis Structures | JoVE K12

chemistry

JoVE Core 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Physical Science

Study Of Matter

Bonding and compounds

Structure And Properties Of Matter

Chemical bonding

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.d

Physics

PH.9

PH.9.e

new-york-state-science-learning-standards

New York State Science Learning Standards

High School

HS. Structure and Properties of Matter

HS-PS1-3.

HS. Chemical Reactions

HS-PS1-2.

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

The Scientific Method

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Use models to explain how the scientific understanding of atomic structure has evolved.

PS.Chm.1.1

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

molecular-comparison-of-gases-liquids-and-solids

Molecular Comparison of Gases, Liquids, and Solids

Particles in a solid are tightly packed together (fixed shape) and often arranged in a regular pattern; in a liquid, they are close together with no ...

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions ...

comparing-intermolecular-forces-melting-point-boiling-point

Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

surface-tension-capillary-action-and-viscosity

Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded ...

Construct an explanation to summarize the influences intermolecular forces have on the properties of chemical compounds.

PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Resonance Forms in Lewis Structures

Description

Transcript

More videos by Standards