Name: forces between molecules
Uploaded: 2020-11-23T11:47:33.000Z
Duration: 3 min 13 s
Channel: JoVE

存在于分子之间的分子间作用力 来源于 电荷、部分电荷和暂时电荷之间的静电相互作用。所有分子都会产生暂时电荷。由于电子分布的变化，电子云某一区域较高的电子密度 会导致瞬时偶极子 或暂时偶极子。随后，这会在邻近分子中诱导出 另一个瞬时偶极子。偶极子的多米诺效应产生 弱分子间吸引力，称为色散力，这存在于所有分子 包括极性和非极性）之间。一些共价化合物，例如水，由于原子的负电性差异而 表现出富电子和贫电子区域。共享电子的不均匀分布 和化合物的分子形状会产生永久性的 部分电荷，导致 在原本为中性的化合物中产生永久性的偶极子，从而使其变成极性。具有永久偶极子的分子 也称为极性化合物）会通过偶极-偶极力进行自我排列，其中一个分子的正电端 会与相邻分子的负电端 产生静电相互作用。如果极性化合物包含 共价键合到小而电负性高的原子 例如氟、氧或氮）的氢原子，则相应地这些原子往往会表现出更大的部分电荷。因此，F-H、O-H 或 N-H 键中的氢原子 会通过一种称为氢键的特殊类型偶极-偶极力 与邻近的电负性原子 发生强烈的相互作用。值得注意的是，氢键比偶极-偶极力强，并且能够形成氢键的化合物会表现出 更高的熔点和沸点。与分子内力相比，这三种分子间力 色散力、偶极-偶极力 和氢键 相对较弱，强度也各不不同。它们统称为范德华力。虽然所有分子（极性或非极性分子）之间都存在色散力，但偶极-偶极力 和氢键只存在于极性分子周围。离子偶极力是溶液所独有的，它是最强的分子间力。当像氯化钠这样的离子化合物溶解 在像水这样的极性溶剂中时，离解的离子 会通过强离子-偶极力与溶剂的偶极子相互作用。请看这里，阳离子与水分子的负电端产生关联，而阴离子 与正电端相互作用。

分子间作用力

Intermolecular Forces

原子和分子通过键 (或力) 相互作用：分子內和分子间。 力是静电，因为它们是由荷电物种 (永久，部分或临时荷) 之间的相互作用 (有吸引力或强推) 引起的，并且在离子，极性，非极性和中性分子之间存在强度不同的情况。 不同类型的分子间作用力包括离子偶极，偶极，氢键和分散；其中 中性原子和分子之间存在偶极，氢键和色散力，统称为范德华力（即：分子间作用力）。 
 偶极 - 偶极力 
 极性分子的一端有部分正电荷，另一端有部分负电荷—电荷分离，称为偶极。 在 HCL 等极分子中，电离性越强的 CL 原子具有部分负电荷，而电离性越低的 H 原子具有部分正电荷。 HCL 分子之间的力很有吸引力，这是因为一个 HCL 分子正端和另一个 HCL 分子负端之间有吸引力。 这种极具吸引力的力被称为偶极吸引力—一个极分子的部分正端和另一个极分子的部分负端之间的静电力。 
 色散力 
 三种范德华力（即：分子间作用力）中的一种存在于所有的冷凝阶段，而不管构成该物质的原子或分子的性质如何。 这位极具吸引力的力被称为伦敦色散力，以纪念德国出生的美国物理学家 弗里茨·伦敦（Fritz London） ，他于 1928 年首次对此进行解释。 此力通常简称为色散力。 由于原子或分子的电子处于恒定运动状态 (或者，它们的位置受量子机械变异的影响) ，因此，如果原子或分子的电子不对称分布，那么在任何时候，它都可以产生一个瞬时的临时偶极。 这种偶极的存在反过来会扭曲邻近原子或分子的电子，产生诱导性偶极。 这两个快速波动的临时偶极因此导致物种之间的静电吸引力相对较弱—一个所谓的色散力。 
 在不同分子的原子之间形成的色散力可以相互吸引这两个分子。 但是，力相对较弱，只有当分子非常接近时才会变得重要。 更大和更重的原子和分子表现出比更小和更轻的原子和分子更强的色散力。 F2 和 Cl2 是室温下的气体 (反映出吸引力较弱的力) ； BR2 是液体， I2 是固体 (反映出吸引力较强的力)。 
 氢键 
 硝基氟化物 (ONF ，分子质量 49 AMU) 是室温下的气体，而水 (H2O ，分子质量 18 AMU) 是液体，即使其分子质量较低。 两个分子的形状大致相同， ONF 是一个更重，更大的分子。 因此，预计它将体验到更重要的色散力。 此外，沸点的这种差异不能是分子偶极点的差异所造成的。 这两个分子都是极性的，表现出类似的偶极点。 沸点之间的巨大差异是由于当分子含有氟，氧气或氮原 (三个最具电子反应的元素) 的氢原子键合时，可能会出现特别强烈的偶极吸引力。 H 原子 (2.1) 和键合原子之间的电负性差异很大 (F 原子 4.0 ， O 原子 3.5 ， 或 3.0 (对于 N 原子) ，加上极小尺寸的 H 原子和相对较小尺寸的 F ， O 或 N 原子，导致这些原子的部分电荷高度集中。 含有 F-H ， O-H 或 N-H 成分的分子被附近分子中类似的成分所强烈吸引，这是一种特别强烈的偶极 - 偶极吸引物，称为氢键。 氢键的示例包括 HF⋯HF ， H2O⋯Hoh 和 H3N⋯HNH2 ，其中氢键以点表示。 
  离子偶极力 
 离子偶极力是离子和偶极之间的静电吸引力。 这些力在溶液中很常见，在水中溶解离子化合物方面发挥着重要作用。 
 
 
 当向水等极溶剂添加离子化合物 (如 KCl) 时，固体中的离子会分离并均匀分散。 离子偶极力将极性水分子的正 (氢) 端吸引到固体表面的负氯化离子，并将负 (氧) 端吸引到正钾离子。 水分子围绕单个 K+ 和 CL− 离子，减少了将离子 (固体中) 联结在一起的强离子力，并让它们作为溶解离子移出溶液。 通过消除静电吸引，当离子从未溶解化合物中的固定位置过渡到溶液中分布广泛的溶解离子时，可以在稀释溶液中独立移动每个水合物。 
 离子 - 偶极相互作用的强度与 i) 离子电荷和 ii) 极性分子的偶极量成正比。 
 本文改编自<a href="https://openstax.org/books/chemistry-2e/pages/10-introduction">Openstax, 化学 2e, 第10章：液体与固体</a>。

原子与分子通过化学键（或作用力）发生相互作用，包括分子内作用力和分子间作用力。这些作用力本质上是静电性的，源于带电粒子之间的相互作用……

Education

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JoVE Core

Molecular Biology

分子生物学

Unit 1

第一单元

Biochemistry of the Cell

细胞生物化学

KEY TERMS AND CONCEPTS

关键术语与概念

forces between molecules

Forces between molecules help explain why matter behaves the way it does. These intermolecular attractions act between separate molecules, not within a single molecule. They are often much weaker than the bonds that hold atoms together inside a molecule, but they still affect many properties of liquids and solids.

Several common types of intermolecular forces are covered in this topic. These include dipole-dipole forces, hydrogen bonding, ion-dipole forces, and van der Waals forces. Van der Waals forces are also called dispersion forces or London dispersion forces.

These attractions help determine how molecules stick together and how they move past one another. In liquids, they influence flow and boiling behavior. In solids, they help shape the structure and stability of the material.

Forces Between Molecules

the periodic table and organismal elements

the-periodic-table-and-organismal-elements

Element Groups in Living Things

Living things are built from elements found on the periodic table. This page focuses on the elements that make up organisms and how they are grouped in biology. These organismal elements are usually divided into major, minor, and trace categories. Major elements make up most of the mass of living matter. Minor elements are needed in smaller amounts. Trace elements are present in very small amounts but still play important roles. The periodic table helps show where these elements fit and how...

functional groups

Functional Groups in Organic Molecules

Functional groups are the parts of organic molecules that give them specific chemical behavior. They help determine how a compound reacts and what properties it has. In organic chemistry, these groups are used to classify molecules in a clear way. Hydrocarbons are one common class of organic compounds. They contain only carbon and hydrogen. Alcohols, aldehydes, and ketones are other classes that are identified by their functional groups. These groups make each class behave differently from the...

polymers

Polymer Structures and Uses

Polymers are large molecules built from repeating smaller units called monomers. Their long-chain structure gives them many different properties and makes them useful in everyday materials. Polymers can form in two main ways. In addition polymerization, monomers join together without losing any atoms. In condensation polymerization, monomers link while a small molecule is released. These two pathways help explain how many common plastics and related materials are made. The structure of a...

what are lipids?

Lipids in Cells: Fats and Membranes

Lipids are a group of biomolecules found in living things. They are known for their role in energy storage and in building cell membranes. This makes them important in many parts of biology. Fats are one common type of lipid. Other lipids include phospholipids and steroids. Each group has a different structure and a different job in the body. Phospholipids are especially important because they help form cell membranes. Steroids also belong to the lipid group, and they have their own distinct...

structure of lipids

Types of Lipids and Their Structure

Lipids are a major group of biological molecules, and their structure helps explain their different forms. Many lipids are built from fatty acids, which are long hydrocarbon chains with a carboxyl group. The carbon chain is hydrophobic, meaning it does not mix well with water, while the carboxyl group is the acidic end. Triglycerides are one common lipid type. They consist of a glycerol molecule joined to three fatty acid chains. Saturated triglycerides have fatty acids with only single...

chemistry of carbohydrates

Carbohydrate Structures and Types

Carbohydrates are biomolecules built from carbon, hydrogen, and oxygen. Their chemistry helps explain how simple sugars join together and how larger carbohydrate molecules form. The smallest carbohydrates are monosaccharides, or single sugar units. These can link to make disaccharides, which contain two sugar units, and polysaccharides, which are long chains of many sugar units. Carbohydrates play an important role in biology because they are part of the structures and processes found in...

nucleic acids

Nucleic Acids and Genetic Information

Nucleic acids carry genetic information in cells. They include DNA and RNA, which are made from nucleotide building blocks. These molecules store, copy, and help use the instructions needed for life. DNA is the main long-term storage molecule for genetic information. RNA helps carry and use that information in cells. Together, these nucleic acids connect the code in a cell to the proteins it can make.

intermolecular forces

Forces between molecules help explain why matter behaves the way it does. These intermolecular attractions act between separate molecules, not within a single molecule. They are often much weaker than the bonds that hold atoms together inside a molecule, but they still affect many properties of liquids and solids. Several common types of intermolecular forces are covered in this topic. These include dipole-dipole forces, hydrogen bonding, ion-dipole forces, and van der Waals forces. Van der...

noncovalent attractions in biomolecules

How Biomolecules Hold Their Shape

Biomolecules hold their shape through noncovalent attractions. These interactions occur within and between molecules and help control the structure and stability of complexes. They are different from covalent bonds because they do not involve sharing electrons. Four main noncovalent interactions are important in biology: hydrogen bonds, van der Waals forces, ionic bonds, and hydrophobic interactions. Hydrogen bonds form when a hydrogen atom is covalently bonded to a strongly electronegative...

pH Scale and Acid-Base Balance

pH measures how acidic or basic an aqueous solution is. It is a key way to describe the balance between acids and bases in water-based solutions. The pH scale shows this balance with low values for acidic solutions and high values for basic solutions. Neutral solutions fall in the middle of the scale. Understanding pH helps explain how different substances behave in water. It also helps compare solutions that are more acidic, more basic, or neutral.

hydrolysis of atp

ATP Hydrolysis and Energy Release

ATP hydrolysis is a key chemical reaction in cells that releases energy. ATP, or adenosine triphosphate, is the molecule cells use to store and transfer energy for many processes. During hydrolysis, water breaks the bond in ATP’s terminal phosphate group. This reaction converts ATP into ADP, or adenosine diphosphate, and inorganic phosphate. The released energy can then be used to drive cellular work. High school biology students often see ATP hydrolysis as part of energy transfer in living...

key terms and concepts

Explore the main intermolecular attractions, including dipole-dipole forces, hydrogen bonding, ion-dipole forces, and van der Waals forces, for high school chemistry.

Forces Between Molecules | JoVE K12

molecular biology

JoVE Core 分子生物学通过清晰简洁的动画视频课程展示了细胞的分子过程。此外，在科学家在行动的视频中，这些概念的应用是通过现代实验室中的真实实验演示的。

Forces Between Molecules

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