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

Intermolecular forces, which exist between molecules, originate from electrostatic interactions between charges, partial charges, and temporary charges.
All molecules produce temporary charges. Due to the varying distribution of electrons, a higher electron density in one region of the electron cloud results in an instantaneous dipole, or a temporary dipole.
This subsequently induces another instantaneous dipole in the neighboring molecule. The domino effect of dipoles gives rise to weak intermolecular attractive forces called dispersion forces, which exist between all molecules, whether polar or nonpolar.
Some covalent compounds, like water, for example, exhibit electron-rich and electron-poor regions caused by the atoms&#8217; differences in electronegativity.
The uneven distribution of shared electrons and the molecular shape of the compound create permanent partial charges, resulting in a permanent dipole in the otherwise neutral compound &#8212; making it polar.
Molecules with permanent dipoles &#8212; also called polar compounds &#8212; align themselves through dipole&#8211;dipole forces, where the positive end of one molecule interacts electrostatically with the negative end of the neighboring molecule.
If a polar compound contains a hydrogen atom covalently bonded to a small, highly electronegative atom like fluorine, oxygen, or nitrogen, the atoms tend to exhibit larger partial charges.
Consequently, the hydrogen atom in F&#8211;H, O&#8211;H, or N&#8211;H bonds strongly interacts with the electronegative atom on its neighbor through a special type of dipole&#8211;dipole force called a hydrogen bond.
Notably, hydrogen bonds are stronger than dipole&#8211;dipole forces, and compounds capable of forming hydrogen bonds exhibit higher melting and boiling points.
The three intermolecular forces &#8212; dispersion, dipole&#8211;dipole, and hydrogen bonds &#8212; are, in comparison with intramolecular forces, relatively weak, with varying strengths. They collectively are classified as van der Waals forces.
While dispersion forces are present between all molecules, polar or nonpolar, dipole&#8211;dipole forces and hydrogen bonds exist only around polar molecules.
Exclusive to solutions is the ion&#8211;dipole force, which is the strongest intermolecular force. When an ionic compound like sodium chloride is dissolved in a polar solvent like water, the dissociated ions interact with the solvent&#39;s dipoles via strong ion&#8211;dipole forces.
Here, the cations associate with the negative ends of the water molecules, while the anions interact with the positive ends.

intermolecular forces

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion&#8211;dipole, dipole&#8211;dipole, hydrogen bonds, and dispersion; among these, dipole&#8211;dipole, hydrogen bonds, and dispersion forces exist between neutral atoms and molecules and are collectively known as van der Waals forces.
Dipole&#8211;dipole forces
Polar molecules have a partial positive charge on one end and a partial negative charge on the other end of the molecule&#8212;a separation of charge called a dipole. In a polar molecule like HCl, the more electronegative Cl atom bears the partial negative charge, whereas the less electronegative H atom bears the partial positive charge. An attractive force between HCl molecules results from the attraction between the positive end of one HCl molecule and the negative end of another. This attractive force is called a dipole&#8211;dipole attraction&#8212;the electrostatic force between the partially positive end of one polar molecule and the partially negative end of another.
Dispersion Forces
One of the three van der Waals forces is present in all condensed phases, regardless of the nature of the atoms or molecules composing the substance. This attractive force is called the London dispersion force in honor of German-born American physicist Fritz London who, in 1928, first explained it. This force is often referred to as simply the dispersion force. Because the electrons of an atom or molecule are in constant motion (or, alternatively, their location is subject to quantum-mechanical variability), at any moment in time, an atom or molecule can develop a temporary, instantaneous dipole if its electrons are distributed asymmetrically. The presence of this dipole can, in turn, distort the electrons of a neighboring atom or molecule, producing an induced dipole. These two rapidly fluctuating, temporary dipoles thus result in a relatively weak electrostatic attraction between the species&#8212;a so-called dispersion force.
Dispersion forces that develop between atoms in different molecules can attract the two molecules to each other. The forces are relatively weak, however, and become significant only when the molecules are very close. Larger and heavier atoms and molecules exhibit stronger dispersion forces than do smaller and lighter atoms and molecules. F2 and Cl2 are gases at room temperature (reflecting weaker attractive forces); Br2 is a liquid, and I2 is a solid (reflecting stronger attractive forces).
Hydrogen Bonding
Nitrosyl fluoride (ONF, molecular mass 49 amu) is a gas at room temperature, whereas water (H2O, molecular mass 18 amu) is a liquid, even though it has a lower molecular mass. Both molecules have about the same shape, and ONF is the heavier and larger molecule. It is, therefore, expected to experience more significant dispersion forces. Additionally, this difference in boiling points cannot be the result of differences in the dipole moments of the molecules. Both molecules are polar and exhibit comparable dipole moments. The large difference between the boiling points is due to a particularly strong dipole&#8211;dipole attraction that may occur when a molecule contains a hydrogen atom bonded to a fluorine, oxygen, or nitrogen atom (the three most electronegative elements). The very large difference in electronegativity between the H atom (2.1) and the atom to which it is bonded (4.0 for a F atom, 3.5 for an O atom, or 3.0 for a N atom), combined with the very small size of a H atom and the relatively small sizes of F, O, or N atoms, leads to highly concentrated partial charges with these atoms. Molecules with F-H, O-H, or N-H moieties are very strongly attracted to similar moieties in nearby molecules, a particularly strong type of dipole&#8211;dipole attraction called hydrogen bonding. Examples of hydrogen bonds include HF&#8943;HF, H2O&#8943;HOH, and H3N&#8943;HNH2, in which the hydrogen bonds are denoted by dots.
&#160;Ion&#8211;dipole forces
An ion&#8211;dipole force is the electrostatic attraction between an ion and a dipole. These forces are common in solutions and play an important role in the dissolution of ionic compounds in water.
When an ionic compound like KCl is added to a polar solvent like water, the ions in the solid separate and disperse uniformly. Ion&#8211;dipole forces attract the positive (hydrogen) end of the polar water molecules to the negative chloride ions at the surface of the solid, and they attract the negative (oxygen) ends to the positive potassium ions. The water molecules surround individual K+ and Cl&#8722; ions, reducing the strong interionic forces that bind the ions together (in a solid) and letting them move off into solution as solvated ions. Overcoming the electrostatic attraction permits the independent motion of each hydrated ion in a dilute solution as the ions transition from fixed positions in the undissolved compound to widely dispersed, solvated ions in solution.
The strength of ion&#8211;dipole interactions is directly proportional to i) the charge on the ion and ii) the magnitude of the dipole of polar molecules.
This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/10-introduction">Openstax, Chemistry 2e, Chapter 10: Liquids and Solids</a>.

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

Education

JoVE Core

Molecular Biology

Unit 1

Biochemistry of the Cell

KEY TERMS AND CONCEPTS

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.

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 Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

Forces Between Molecules

Description

Transcript

Tags