Name: how bond polarity shapes molecular dipoles
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 48 s
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K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.1

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Bond Polarity, Dipole Moment, and Percent Ionic Character

化学結合の種類は 非極性共有結合なのか 極性共有結合なのか イオン結合なのかは 結合している原子間の 電子陰性度の差と その結合の長さによって 大きく決まります 臭素では 2つの臭素原子間の 電子陰性度の差がゼロであるため 2つの臭素原子間の結合は 非極性です 臭化水素では 電子陰性度の高い臭素が 電子陰性度の低い水素原子から 電子密度を引き離すため 結合は極性共有結合です 臭化カリウムでは 電子陰性度の差が大きいため 結合はイオン結合となり カリウムから臭化水素への 完全な電子移動が行われます 同じように帯電していても 反対に帯電している 2つの粒子が距離を隔てて 双極子が形成されます この双極子の定量的な尺度は 電荷の大きさQ（クーロン）と 電荷間の 距離r（メートル）の積である muという文字で表され 双極子モーメントと 呼ばれています 双極子モーメントは デバイ単位で与えられ 1デバイは 3.34×10^30 C*mです 化合物が極性共有または イオン性であるかどうかは 完全な電子移動を仮定した 双極子モーメントに対する 結合の測定された 双極子モーメントの比である パーセントイオン性の 特性を計算することによって 決定することができます 50%以上のイオン性結合は イオン性とみなされます 水素原子とフッ素原子が 92pmの距離で 隔てられている フッ化水素を考えてみましょう この結合がイオン性の場合 電子が完全に移動したと仮定して 双極子モーメントを計算します 電子の電荷に 原子間距離を乗じて 得られた値を1デバイで割ると 4.41Dの双極子モーメントが 得られます しかしフッ化水素の 実験的に測定された双極子 モーメントは1.18Dです したがってフッ化水素の イオン性を求めるためには 測定値1.18Dを4.41Dで 割ることになります 41 Dで割ると 41%のイオン性が得られます フッ化水素のパーセント イオン性は50%未満であり 極性共有結合であることが わかります

結合の極性、双極子モーメント及びイオン特性

<h4>結合の極性 </h4>
 
 結合している2つの原子の電気陰性度の差（ΔEN）の絶対値は、結合に期待される極性の大まかな尺度となり、したがって結合の種類を示します。この差が非常に小さいかゼロの場合、その結合は共有結合であり、無極性です。その差が大きい場合は、極性のある共有結合またはイオン結合です。H-H、H-Cl、Na-Clの結合における原子間の電気陰性度の差の絶対値は、それぞれ0（非極性）、0.9（極性共有結合）、2.1（イオン性）です。
 
 原子間で電子を共有する度合いは、完全に等しいもの（純粋な共有結合）から全くないもの（イオン結合）まで様々です。
 
 <ul>
 <li>例えば、HFのH原子とF原子の電気陰性度の差は1.9で、NH3のN原子とH原子の電気陰性度の差は0.9ですが、これらの化合物はどちらも極性共有結合とみなされる結合を形成しています。</li>
 <li>同様に、NaClのNa原子とCl原子の電気陰性度の差は2.1であり、MnI2のMn原子とI原子の電気陰性度の差は1.0ですが、いずれもイオン化合物を形成しています。 </li>
 </ul>
 
 結合の性質が共有結合かイオン結合かを判断する最良の方法は、関係する原子の種類と周期表における相対的な位置を考慮することです。
 
 <ul>
 <li>2 つの非金属間の結合は一般に共有結合です。 </li>
 <li>金属と非金属の結合は、イオン性が高いことが多いです。 </li>
 </ul>
 
 化合物の中には、共有結合とイオン結合の両方を含むものがあります。OH–、NO3−、NH4+などの多原子イオンの原子は、極性のある共有結合によって結合しています。しかし、これらの多原子イオンは、反対の電荷を持つイオンと結合することで、イオン性の化合物を形成します。例えば、硝酸カリウム（KNO）は、K+イオンと多原子NO3−イオンを含んでいます。このように、硝酸カリウムの結合は、K+イオンとNO3−イオンの間の静電引力に起因するイオン結合と、NO3−の窒素原子と酸素原子の間の共有結合です。 
 
 <h4>分子極性と双極子モーメント </h4>
 
 前述したように、極性共有結合は、電気陰性度の異なる2つの原子を結合するもので、電子が電気陰性度の高い原子に引っ張られることにより、一方の原子は部分的に正の電荷（δ+）を、もう一方の原子は部分的に負の電荷（δ-）を持つことになります。このような電荷の分離により、結合双極子モーメントが発生します。結合双極子モーメントの大きさは、ギリシャ文字のmu（µ）で表され、Qは部分電荷の大きさ（電気陰性度の差で決まる）、rは電荷間の距離で、次の式で与えられます。 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/1062/1062_Equations-01.png" style="height: 40px;" />
 
 この結合モーメントは、方向と大きさを持つ量であるベクトルとして表すことができます。双極子のベクトルは，電気陰性の原子から電気陰性の原子に向かって，結合に沿って矢印で示されます。電気陰性度の低い方の端に小さなプラス記号を描き、結合の部分的にプラスの端を示しています。矢印の長さは，2つの原子の電気陰性度の差の大きさに比例します。 
 
 また、分子構造や各結合の極性によって、分子全体に電荷の分離が生じることがあります。このような電荷分離がある場合、その分子は極性分子（または双極子）と呼ばれ、そうでない場合は非極性分子と呼ばれます。双極子モーメントは、分子全体の正味の電荷分離の程度を示すものです。双極子モーメントは、分子構造を考慮した上で、3次元空間における結合モーメントを加算して求められます。 
 
 二原子分子の場合、結合は1つしかないので、結合の双極子モーメントが分子の極性を決定することになります。Br2やN2のような同核の二原子分子では、電気陰性度の差がないので、双極子モーメントはゼロです。COのような異核分子では、小さな双極子モーメントがあります。HFの場合は電気陰性度の差が大きいので、より大きな双極子モーメントがあります。 
 
 分子内に複数の結合がある場合、その形状を考慮しなければなりません。分子内の結合が、その結合モーメントが相殺される（ベクトル和がゼロになる）ように配置されていれば、その分子は非極性です。これは、CO2の場合です。それぞれの結合は極性を持っていますが、分子全体としては非極性です。ルイス構造から、VSEPR理論を用いて、CO2分子は、炭素原子の反対側に極性のあるC=O結合を持つ直線状の分子であることが決定されます。結合モーメントは、反対方向に向いているため、相殺されます。水分子の場合も、ルイス構造から、中央の原子に2つの結合があることがわかり、電気陰性度の違いから、それぞれの結合がゼロでない結合モーメントを持つことがわかります。しかし、この場合は、Oの孤立電子対のために分子構造が曲がっており、2つの結合モーメントは相殺されません。したがって、水には正味の双極子モーメントがあり、極性分子（双極子）であることがわかります。 
 
 本書は <a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">、 Openstax 、 Chemistry 2e 、 Chapter 7.2 ： Coalent Bonding and Openstax 、 Chemistry 2e 、 Chapter 7.6 Molecular Structure and Polarity から引用しています。</a>

ボンド極性

結合した2つの原子の電気陰性度(ΔEN)の差の絶対値は、極性の大まかな尺度を提供します...

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

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 is ionic. Even so, ΔEN is only a guide. HF has a ΔEN of 1.9 and NH3 has a ΔEN of 0.9, yet both have polar covalent bonds. NaCl has a ΔEN of 2.1 and MnI2 has a ΔEN of 1.0, yet both are ionic compounds.

The type of atoms in the periodic table is often the best clue. Bonds between two nonmetals are generally covalent. Bonds between a metal and a nonmetal are often ionic. Some compounds include both kinds of bonding. Polyatomic ions such as OH−, NO3−, and NH4+ have polar covalent bonds inside the ion. They form ionic compounds when they combine with ions of the opposite charge. Potassium nitrate, KNO3, is one example. It contains K+ and NO3−, so the attraction between those ions is ionic, while the N–O bonds inside nitrate are covalent.

Polar covalent bonds create partial charges, written as δ+ and δ−. The more electronegative atom pulls the electrons closer, so one end of the bond becomes partially negative and the other becomes partially positive. This charge separation creates a bond dipole moment, symbolized by μ. A dipole is shown as a vector, or arrow, that points from the less electronegative atom toward the more electronegative atom. A small plus sign marks the positive end. A longer arrow means a larger electronegativity difference.

A whole molecule can also have a net dipole moment. That depends on both bond polarity and molecular shape. The dipole moment of the molecule is found by adding the bond moments in three-dimensional space. For diatomic molecules, there is only one bond, so the bond dipole sets the molecular polarity. Homonuclear diatomic molecules such as Br2 and N2 have no electronegativity difference, so their dipole moment is zero. Heteronuclear molecules such as CO have a small dipole moment, and HF has a larger one because its electronegativity difference is larger.

Molecular geometry can make polar bonds cancel. CO2 is linear, so its two polar C=O bond moments point in opposite directions and cancel. The molecule is nonpolar even though its bonds are polar. Water is different. Its Lewis structure shows two bonds to oxygen, and each bond has a nonzero dipole moment. Because the molecule is bent, the bond moments do not cancel. Water therefore has a net dipole moment and is a polar molecule.

How Bond Polarity Shapes Molecular Dipoles

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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...

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Predicting Ionic Stability with Lattice Energy

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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...

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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

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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 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

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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...

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Resonance Forms in Lewis Structures

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Lewis Structures with Formal Charge

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Octet Rule Exceptions in Lewis Structures

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How Bond Energy Predicts Reaction Heat

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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 electronegativity, bond dipoles, and molecular shape determine whether a bond or molecule is polar, using examples like HCl, CO2, and water.

How Bond Polarity Shapes Molecular Dipoles | 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。

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Physical Science

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Matter and Its Interactions

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CHEM1.PS1.14

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CH.3.d

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Motion and Stability: Forces and Interactions

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Chemistry and Physics

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Matter: Pure Substances and Mixtures
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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

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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 ...

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

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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 ...

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Atomic Orbitals

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The Pauli Exclusion Principle

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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 ...

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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

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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

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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

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 ...

Resonance

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.

Analyze the structure of atoms and isotopes.

How Bond Polarity Shapes Molecular Dipoles

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