10.1 Intermolecular Forces
3 min read•june 25, 2024
Molecules attract each other through different forces. These range from weak in nonpolar molecules to strong hydrogen bonds in water. Understanding these forces helps explain why substances behave differently.
impact physical properties like boiling points and . Stronger forces mean higher boiling points and more resistance to flow. This knowledge helps predict and explain the behavior of various substances in everyday life.
Types of Intermolecular Forces
Explain the three main types of intermolecular forces: dispersion forces, dipole-dipole attractions, and hydrogen bonding
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- Dispersion forces ()
- Weakest intermolecular force present in all molecules, including nonpolar ones (, , )
- Caused by temporary, instantaneous dipoles resulting from the random movement of electrons creates brief attractive forces
- Strength increases with increasing molecular size and surface area more electrons and larger surface area enhance dispersion forces
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- Stronger than dispersion forces occur between polar molecules with permanent dipoles (, , )
- Positive end of one dipole attracts the negative end of another dipole leading to net attractive force
- Strength depends on the magnitude of the dipole moments larger dipole moments result in stronger attractions
-
- Strongest intermolecular force a special type of
- Occurs when a hydrogen atom is bonded to a highly electronegative atom (N, O, or F) in molecules like , , , alcohols, amines, and carboxylic acids
- The small size of hydrogen allows for close approach and strong electrostatic attraction between the positive H and negative N, O, or F
Prediction of Intermolecular Forces
Predict the intermolecular forces present in substances based on molecular structure
- Nonpolar molecules
- Only dispersion forces are present since there are no permanent dipoles
- Examples include simple diatomic gases (, ) and symmetrical hydrocarbons ()
- Polar molecules without H bonded to N, O, or F
- Dispersion forces and dipole-dipole attractions are present due to permanent dipoles
- Examples include polar molecules like , , and
- Polar molecules with H bonded to N, O, or F
- Dispersion forces, dipole-dipole attractions, and hydrogen bonding are present
- Examples include water (), ammonia (), hydrogen fluoride (), alcohols, amines, and carboxylic acids
Impact on Physical Properties
Connect intermolecular forces to physical properties, especially melting and boiling points
- Stronger lead to higher melting and boiling points
- More energy is required to overcome the attractive forces between molecules and break them apart
- Substances with only dispersion forces (noble gases, nonpolar hydrocarbons) tend to have lower melting and boiling points
- Substances with dipole-dipole attractions have higher melting and boiling points than those with only dispersion forces
- Comparing (dispersion forces only) and (dispersion forces and dipole-dipole attractions) shows the impact of dipole-dipole forces
- Substances with hydrogen bonding have the highest melting and boiling points among molecules of similar size
- Comparing (hydrogen bonding) and (dipole-dipole attractions) demonstrates the strength of hydrogen bonds
- Intermolecular forces also affect other physical properties
- : stronger forces lead to higher viscosity (resistance to flow)
- : stronger forces lead to higher (resistance to breaking the surface)
- Vapor pressure: stronger forces lead to lower vapor pressure (less tendency to evaporate)
Effects of Intermolecular Forces on Liquid Properties
- : the attraction between molecules of the same substance, which is stronger in liquids with stronger intermolecular forces
- : the attraction between molecules of different substances, which can lead to wetting of surfaces
- Surface tension: the tendency of liquid surfaces to shrink into the minimum surface area possible, caused by the cohesive forces between molecules
- : the ability of a liquid to flow against gravity in narrow spaces, resulting from the combined effects of cohesion and adhesion
Key Terms to Review (30)
Adhesion: Adhesion is the attractive force that exists between the surfaces of two different materials, causing them to cling or stick together. This intermolecular force is crucial in various chemical and physical processes, particularly in the context of 10.1 Intermolecular Forces.
Autumn: Autumn is one of the four temperate seasons, occurring between summer and winter. It is characterized by cooler temperatures and the changing color of leaves.
Capillary action: Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces. It occurs due to the adhesive force between the liquid and the surface and the cohesive forces within the liquid.
Capillary Action: Capillary action, also known as capillarity, is the ability of a liquid to flow through narrow spaces without the assistance of, and in opposition to, external forces like gravity. It is driven by intermolecular attractive forces between the liquid and the surrounding solid surfaces, and is an important factor in the properties and behavior of liquids.
Cohesion: Cohesion refers to the attractive forces that exist between like molecules, causing them to cling together and form a more organized and stable structure. This concept is particularly relevant in the context of intermolecular forces, which govern the interactions between molecules and shape the physical properties of substances.
Coulomb's Law: Coulomb's law is a fundamental principle in electrostatics that describes the force of interaction between two stationary electric charges. It states that the force between two charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.
Dipole-dipole attraction: Dipole-dipole attraction is an intermolecular force between polar molecules, where the positive end of one molecule is attracted to the negative end of another. This type of interaction is stronger than London dispersion forces but weaker than hydrogen bonds.
Dipole-Dipole Attractions: Dipole-dipole attractions are a type of intermolecular force that occurs between polar molecules, where there is an unequal sharing of electrons resulting in a partial positive charge on one end and a partial negative charge on the other end of the molecule. These attractions help to hold polar molecules together.
Dispersion Forces: Dispersion forces, also known as London dispersion forces, are a type of intermolecular force that arises from the temporary, fluctuating dipoles that can form in all atoms and molecules. These forces play a crucial role in the structure and general properties of nonmetals.
Electronegativity: Electronegativity is a measure of an atom's ability to attract and hold onto electrons within a chemical bond. It is a dimensionless quantity usually assigned values on the Pauling scale.
Electronegativity: Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond. It is a fundamental property that influences the nature and strength of chemical bonds, as well as the physical and chemical properties of substances.
Hu: Hu is not a standard term in chemistry. It appears to be an error or abbreviation not recognized within the context of liquids, solids, or intermolecular forces. If it refers to something specific like a scientist's name or a unique concept, please provide more context.
Hydrogen Bonding: Hydrogen bonding is a type of dipole-dipole intermolecular force that occurs when a hydrogen atom covalently bonded to a highly electronegative element, such as nitrogen, oxygen, or fluorine, experiences an attractive force with another nearby highly electronegative element. This attractive force is significantly stronger than a typical dipole-dipole interaction and has a significant impact on the physical and chemical properties of various compounds.
Induced dipole: An induced dipole occurs when the electron distribution in a neutral atom or molecule is distorted by an external electric field, causing a temporary dipole moment. This phenomenon is typically weak and short-lived, dependent on the presence of nearby charges.
Induced Dipole: An induced dipole is a temporary separation of charge within a molecule or atom that occurs when the molecule or atom is placed in an external electric field. This separation of charge creates a dipole moment, which can influence the intermolecular forces between molecules.
Instantaneous dipole: An instantaneous dipole occurs when the electrons in an atom or molecule are distributed asymmetrically at a given moment, creating a temporary dipole. This transient phenomenon leads to induced dipoles in adjacent molecules and results in intermolecular attractions known as London dispersion forces.
Intermolecular forces: Intermolecular forces are the forces of attraction and repulsion between molecules that influence the physical properties of substances. These forces are weaker than intramolecular forces, which hold atoms together within a molecule.
Intermolecular Forces: Intermolecular forces are the attractive or repulsive forces that exist between molecules, as opposed to the intramolecular forces that hold atoms together within a molecule. These forces play a crucial role in determining the physical properties and behavior of substances across various topics in chemistry, including non-ideal gas behavior, the properties of liquids, phase transitions, and the dissolution process.
Johannes van der Waals: Johannes van der Waals was a Dutch physicist who made significant contributions to the understanding of intermolecular forces and the behavior of gases. His work on the concept of van der Waals forces, which describe the attractive and repulsive interactions between molecules, has been crucial in the field of physical chemistry and the study of intermolecular forces.
London: London dispersion forces are weak intermolecular forces arising from temporary shifts in electron density, creating instantaneous dipoles. They are present in all molecules but are the only intermolecular force in nonpolar molecules.
London dispersion force: London dispersion forces are weak intermolecular forces arising from temporary dipoles induced in atoms or molecules. They are present in all molecular interactions but are the only type of intermolecular force in nonpolar compounds.
London Dispersion Forces: London dispersion forces are a type of intermolecular force that arises from the temporary, spontaneous polarization of atoms or molecules. These forces are the weakest of the intermolecular forces, but they play a crucial role in the properties and behavior of many substances, including liquids, gases, and the noble gases.
Polarity: Polarity refers to the unequal distribution of electrons within a molecule, resulting in the creation of partially positive and partially negative regions. This concept is fundamental in understanding the properties and behavior of ionic, molecular, and organic compounds.
Polarizability: Polarizability is the measure of how easily an electron cloud around a molecule can be distorted by an external electric field, resulting in a temporary dipole. It is an important factor in determining the strength of intermolecular forces.
Surface tension: Surface tension is the energy required to increase the surface area of a liquid due to intermolecular forces. It causes the liquid to behave as if its surface were covered with a stretched elastic membrane.
Surface Tension: Surface tension is a property of liquids that arises from the cohesive forces between the molecules at the liquid's surface. It is what allows some insects to walk on water and causes liquids to rise in narrow tubes against the force of gravity.
Van der Waals forces: Van der Waals forces are weak intermolecular forces that arise from the interactions between induced or permanent dipoles in molecules. They play a crucial role in determining the physical properties of liquids and solids.
Van der Waals Forces: van der Waals forces are a type of weak intermolecular attractive forces that arise between neutral atoms or molecules. These forces are responsible for the non-ideal behavior of gases, the properties of liquids and solids, and the structure and general properties of nonmetals and noble gases.
Viscosity: Viscosity is a measure of a liquid's resistance to flow. It quantifies the internal friction within the fluid.
Viscosity: Viscosity is a measure of the resistance of a fluid to flow. It is a fundamental property of liquids that describes their internal friction and ability to resist deformation under shear stress. Viscosity is an important factor in understanding the behavior and properties of liquids, as it directly impacts their flow characteristics.