Name: shared electrons in covalent molecules
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 46 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

Covalent Bonding and Lewis Structures

共有結合は 非金属同士が 価電子を共有することで 形成されます しかし なぜ非金属は イオン結合のように 電子を移動させるのではなく 共有するのでしょうか？非金属はイオン化エネルギー が高いため 原子間で価電子を 共有結合は移動させることが 難しいからです アンモニアの分子を 考えてみましょう 窒素原子は オクテットに到達するには さらに3個の電子を必要とし 水素原子は デュエットに到達するには 1個の電子を必要とします そのため 窒素原子は 3つの水素原子と結合し 窒素と水素の両方が安定な 電子配置になるようにします これらの結合は それぞれが 1対の電子を共有しているので 単結合と呼ばれています 共有結合で共有された 電子対を 結合対と呼びます 結合に参加していない価電子は ローンペアまたは 非結合電子と呼ばれています 6個の原子価電子を持つ 酸素原子は 1オクテットに到達するために さらに2個の電子が必要です そのため 2つの酸素原子は 2電子対を共有して 二重結合を形成します 一方 窒素は その二原子の形で 3つの不対電子を共有しており 三重結合を形成しています 単結合と多重結合では 結合の長さや強さが異なります 三重結合は二重結合よりも短く 単結合よりも短くなっています 結合の多重度が高くなると 結合強度が高くなります そのため 窒素中では 三重結合が壊れにくく 比較的反応性が低くなります ルイスモデルは 分子の構造や安定性を 予測するのに役立ちます ルイスモデルによると H2Oは安定な分子です なぜなら 酸素と水素の両方が 安定した電子配置を 達成しているからです もし酸素が水素原子1個と 電子を共有すると 酸素は7個の価電子しか持たず オクテットに到達できないため 結果として得られるOH分子は 安定ではありません しかし 酸素に 余分な電子を加えて オクテットを完成させると 得られる水酸化物イオンは 負の電荷を帯びて安定になります 共有結合は共有電子が2つの 特定原子のペアをリンクしており 方向性があります 対照的に イオン結合は 無方向性であり 格子内の複数の イオンを保持します このように共有結合性化合物では 個々の分子は 基本的な単位であると 考えられています

共有結合とルイス構造

金属原子と非金属原子の間で電子が移動して生じます。イオン結合に比べ、共有結合は、共有された電子のペアを求めて原子が相互に引き合うことで生じます。
 
 共有結合は、2つの原子が自分に電子を引き寄せる傾向が似ている場合（イオン化エネルギーや電子親和力が同じかかなり似ている場合）に形成されます。
 
 <h4>共有結合化合物の物理的特性 </h4>
 
 共有結合を含む化合物は、イオン性化合物とは異なる物理的性質を示します。電気的に中性である分子間の引力は、電気を帯びたイオン間の引力よりも弱いため、共有結合を持つ化合物の融点や沸点は、一般的にイオン性化合物よりもはるかに低いです。実際、共有結合を持つ化合物の多くは、室温では液体や気体であり、固体状態ではイオン性固体よりもはるかに柔らかいです。さらに、イオン性化合物は水に溶けると電気をよく通しますが、共有結合性化合物の多くは水に溶けず、電気的に中性であるため、どのような状態でも電気をよく通しません。 
 
 <h4>共有結合の形成 </h4>
 
 非金属原子は、しばしば他の非金属原子と共有結合を形成します。例えば、水素分子であるH2は、その2つの水素原子の間に共有結合を持っています。特定の位置エネルギーを持つ2つの別々の水素原子が互いに接近すると、それらの価電子軌道（1s）が重なり始めます。そして、それぞれの水素原子上の単一電子は、両方の原子核と相互作用し、両方の原子の周りの空間を占めます。共有された各電子が両方の原子核に強く引きつけられることで系が安定し、結合距離が短くなるにつれてポテンシャルエネルギーも小さくなります。原子同士が接近していくと、両原子核の正電荷が反発し始め、位置エネルギーが増大することになります。最も低い位置エネルギーが得られる距離によって結合長が決まります。
 
 化学結合を壊すにはエネルギーを加えなければならない（吸熱過程）のに対し、化学結合を形成するとエネルギーが放出される（発熱過程）ことを覚えておく必要があります。H2の場合、共有結合が非常に強く、1モルの水素分子の結合を切断して原子を分離させるには、436kJという大量のエネルギーを加えなければなりません。
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/1059/1059_Equations-01.png" style="height: 40px;" />
 
 逆に、 H2 分子の 1 モルが H 原子の 2 モルから形成されると、同じ量のエネルギーが放出されます。 
 
 <img alt="Eq2" src="https://www.jovecore.com/CDNSource/lessons/1059/1059_Equations-02.png" style="height: 40px;" />
 
 <h4>ルイス構造 </h4>
 
 ルイス記号は、分子や多原子イオンの結合を表す図面であるルイス構造で示される共有結合の形成を示すために使用できます。例えば、2つの塩素原子が塩素分子を形成する場合、2つの塩素原子は1対の電子を共有します。 
 
 <img alt="Figure1" src="https://www.jovecore.com/CDNSource/lessons/1059/1059Image_1.svg" style="height: 90px;" />
 
 ルイス構造によると、各Cl原子は、結合に使用されない3つの電子ペア（孤立電子対と呼ばれる）と1つの共有電子ペア（原子間に書かれている）を持っています。共有電子のペアを示すためにダッシュ（またはライン）Cl- Clが使われることもあります。 
 
 <ul>
 <li>電子のペアが1つだけ共有されている状態を「単結合」と呼びます。各Cl原子は8個の価電子と相互作用している：孤立電子対の6個と単結合の2個。 </li>
 <li>しかし、必要なオクテットを達成するためには、一対の原子が1対以上の電子を共有する必要があるかもしれません。二重結合は、CH2O（ホルムアルデヒド）の炭素原子と酸素原子の間や、C2H4（エチレン）の2つの炭素原子の間のように、一対の原子間で2組の電子が共有されている場合に形成されます。 
 <img alt="Figure2" src="https://www.jovecore.com/CDNSource/lessons/1059/1059Image_2.svg" style="height: 120px;" /></li>
 <li>三重結合は、一酸化炭素（CO）とシアン化物イオン(CN–)のように、一対の原子が3つの電子対を共有する場合に形成されます 
 <img alt="Figure3" src="https://www.jovecore.com/CDNSource/lessons/1059/1059Image_3.svg" style="height: 90px;" /></li>
 </ul>
 
 周期表を使えば、原子の価電子の数や、オクテットになるまでの結合数を予測することができます。アルゴンやヘリウムなどの18族元素は、電子配置が満たされているため、化学結合にはほとんど関与しません。しかし、臭素やヨウ素のような17族の原子は、オクテットに達するために必要な電子は1個だけです。そのため、17族に属する原子は1つの共有結合を形成することができます。16族の原子は、オクテットに到達するために2つの電子を必要とするので、2つの共有結合を形成することができます。同様に、第14族に属する炭素は、オクテットに到達するためにさらに4個の電子を必要とするため、炭素は4つの共有結合を形成することができます。
 
 本書は <a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">、 Openstax 、 Chemistry 2e 、 Section 7.2 ： Coalent Bonds</a> and <a href="https://openstax.org/books/chemistry-2e/pages/7-3-lewis-symbols-and-structures">Openstax 、 Chemistry 2e 、 Section 7.3 ： Lewis Symbols and Structures から引用しています。</a>

金属原子と非金属原子の間の電子の移動から生じるイオン結合と比較して、共有結合は相互から生じます...

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

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 have lower melting and boiling points, and some are liquids or gases at room temperature. When they are solids, they are usually softer than ionic solids. Most covalent compounds are also insoluble in water and are poor conductors of electricity in any state.

Hydrogen gas shows how a covalent bond forms. In H2, two hydrogen atoms approach each other and their 1s valence orbitals overlap. Each electron interacts with both nuclei, which lowers the potential energy and stabilizes the molecule. If the atoms move too close, the positive nuclei repel each other, and the potential energy rises. The bond length is the distance where the potential energy is lowest. Forming a bond releases energy, so it is an exothermic process. Breaking a bond requires energy, so it is endothermic. For H2, 436 kJ must be added to break one mole of molecules, and the same amount is released when one mole forms from hydrogen atoms.

Lewis structures show covalent bonding with Lewis symbols. In chlorine gas, Cl2, the two chlorine atoms share one pair of electrons. Each chlorine atom also has three lone pairs, which are pairs not used in bonding. A shared pair can be shown with a dash, so Cl—Cl represents a single bond. Each chlorine atom then has eight valence electrons around it, including lone pairs and the bonding pair.

Some atoms need more than one shared pair to reach an octet, which is a full outer shell of eight electrons. A double bond forms when two pairs of electrons are shared, as in CH2O and C2H4. A triple bond forms when three pairs are shared, as in CO and CN−. The periodic table helps predict bonding patterns from valence electrons. Group 18 elements such as argon and helium already have filled electron configurations and rarely bond. Group 17 atoms, such as bromine and iodine, usually need one electron and can form one covalent bond. Group 16 atoms need two electrons and can form two covalent bonds. Carbon in group 14 needs four more electrons, so it can form four covalent bonds.

Shared Electrons in Covalent Molecules

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

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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

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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

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

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lewis structures of molecular compounds and polyatomic ions

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

Drawing Lewis Structures with Valence Electron Counts

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resonance

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formal charges

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exceptions to the octet rule

Octet Rule Exceptions in Lewis Structures

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bonding in metals

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key terms and concepts

Explore how nonmetal atoms share electrons to form covalent bonds, from H2 and Cl2 to double and triple bonds, Lewis structures, and bonding patterns.

Shared Electrons in Covalent Molecules | 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。

Physical Science

PS.PSc.2.1

Pennsylvania State Academic Standards

Structure and Properties of Matter

3.2.9-12.B

3.2.9-12.N

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Bonding and compounds

Structure And Properties Of Matter

Chemical bonding

Representing compounds

Physical Geology

Minerals

Chemical bonding (ionic, covalent, metallic)

Tennessee Academic Standards

High School

Matter and Its Interactions

CHEM1.PS1.12

CHEM1.PS1.14

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

CHEM1.PS2.1

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.d

PS.3

PS.3.c

Physics

PH.9

PH.9.e

Minnesota Academic Standards in Science

1.2.1 9L.4.2.2.1

Arizona Science Standards

HS.P1

HS.P1U1.2

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

HS-PS1-2

Texas Essential Knowledge and Skills

CHEM.6

CHEM.6.E

Alabama Course of Study Science

9-12.C.2.2.a

9-12.C.2.2.c

Florida Department of Education

SC.912.P.8

SC.912.P.8.6

Chemistry and Physics

IPC.7

IPC.7.A

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Structure and Properties of Matter

HS-PS1-3.

HS. Chemical Reactions

HS-PS1-2.

Georgia Standards of Excellence

SPS2.

Chemical Bonds

SC2.

bonding-types-from-nonpolar-covalent-to-ionic

Bonding Types: From Nonpolar Covalent to Ionic

Scientific Laws and Theories

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PS.Chm.1.1

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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

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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

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

PS.Chm.1.2

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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

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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 ...

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 ...

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PS.Chm.1.3

Periodic Classification of the Elements

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

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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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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

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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

Analyze the structure of atoms and isotopes.

Shared Electrons in Covalent Molecules

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