2.12 Noncovalent Interactions between Molecules
2 min read•may 7, 2024
Noncovalent interactions shape the behavior of molecules in fascinating ways. From the subtle dance of electrons in to the strong embrace of , these forces influence everything from water's unique properties to DNA's structure.
Understanding these interactions is key to grasping how molecules behave in different environments. Whether it's explaining why oil and water don't mix or how proteins fold, noncovalent forces are the invisible hands guiding molecular interactions in chemistry and biology.
Noncovalent Interactions between Molecules
Types of noncovalent molecular interactions
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- Attraction between polar molecules with permanent dipoles (HCl)
- Positive end of one dipole attracts negative end of another dipole
- Strength depends on magnitude of dipoles and their alignment
- Dispersion forces ()
- Present in all molecules, including nonpolar molecules (CH4)
- Arise from temporary, caused by constant motion of electrons
- Strength increases with size and surface area of molecules
- Hydrogen bonds
- Special type of dipole-dipole interaction
- Hydrogen atom bonded to highly atom (N, O, or F) interacts with lone pair of electrons on another electronegative atom
- Stronger than typical dipole-dipole forces but weaker than covalent bonds (water, DNA)
Intermolecular Forces and Molecular Properties
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- Collective term for dipole-dipole, dispersion, and induced dipole interactions
- Contribute to overall intermolecular attraction between molecules
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- Determines the distribution of charge across a molecule
- Influences the strength and type of
- Induced dipoles
- Temporary dipoles created in nonpolar molecules by nearby polar molecules
- Contribute to attractions between polar and nonpolar substances
Effects of hydrogen bonding
- Water
- Hydrogen bonding between water molecules leads to unique properties
- High due to
- High , resisting temperature changes
- Ice floats on liquid water due to open lattice structure in solid state
- Hydrogen bonding between water molecules leads to unique properties
- DNA
- Hydrogen bonding crucial for structure and function
- Complementary base pairing (A-T and G-C) stabilizes double helix
- Contributes to specificity of DNA replication and transcription
- Stabilizes secondary structures in RNA (hairpin loops, stem-loops)
- Hydrogen bonding crucial for structure and function
Hydrophilic vs hydrophobic substances
- substances
- Attract and have affinity for water
- Contain polar or charged functional groups that form hydrogen bonds with water
- Examples: sugar, salt, amino acids, polar solvents (ethanol)
- substances
- Repel or have low affinity for water
- Typically nonpolar, lacking functional groups that form hydrogen bonds with water
- Examples: hydrocarbons (alkanes), fats, oils, nonpolar solvents (hexane)
- substances
- Contain both hydrophilic and hydrophobic regions
- Examples: phospholipids, soaps, detergents
- Phospholipids form bilayers in cell membranes due to amphiphilic nature
- Soaps and detergents remove grease and oil by emulsifying them in water
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- Process by which solute molecules are surrounded by solvent molecules
- Crucial for understanding dissolution and solubility in various solvents
Key Terms to Review (17)
Amphiphilic: Amphiphilic molecules possess both hydrophilic (water-loving) and hydrophobic (water-fearing) properties, allowing them to interact with both polar and nonpolar environments. This unique characteristic makes amphiphiles essential in various contexts, including noncovalent interactions between molecules and the formation of soap.
Cohesive Forces: Cohesive forces are the attractive intermolecular forces that hold molecules together within a substance, contributing to the physical and chemical properties of that substance. These forces are particularly relevant in the context of noncovalent interactions between molecules.
Dipole-Dipole Forces: Dipole-dipole forces are a type of intermolecular force that occurs between polar molecules, where there is an uneven distribution of electrons resulting in a partial positive and partial negative charge within the molecule. These attractive forces arise from the electrostatic interactions between the oppositely charged regions of neighboring molecules.
Dispersion Forces: Dispersion forces, also known as London dispersion forces, are a type of van der Waals force that arise due to the temporary, instantaneous formation of dipoles in atoms or molecules. These forces are the weakest of the intermolecular forces, but they play a crucial role in the noncovalent interactions between molecules.
Electronegative: Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond. Atoms with high electronegativity values are considered electronegative, meaning they have a strong tendency to attract electrons towards themselves.
Hydrogen Bonds: Hydrogen bonds are a type of noncovalent interaction that occurs when a hydrogen atom covalently bonded to a highly electronegative element, such as nitrogen, oxygen, or fluorine, is attracted to another nearby highly electronegative element. This attractive force is significantly stronger than a typical dipole-dipole interaction and plays a crucial role in the structure and properties of various molecules and biological systems.
Hydrophilic: Hydrophilic refers to the affinity of a molecule or surface for water. Substances that are hydrophilic readily interact with, dissolve in, or are attracted to water, making them water-loving or water-soluble.
Hydrophobic: Hydrophobic refers to the aversion or repulsion of water molecules by certain molecules or surfaces. This property arises from the inability of water to form hydrogen bonds with these substances, leading to a minimization of contact between the water and the hydrophobic entity.
Induced Dipoles: Induced dipoles are temporary, instantaneous dipole moments that arise in molecules or atoms when they are in the presence of an external electric field or another polar molecule. This occurs due to the slight separation of positive and negative charges within the molecule, creating a temporary dipole.
Intermolecular forces: Intermolecular forces are the forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions). They are crucial for determining the physical properties of substances, such as boiling points, melting points, and solubilities.
Intermolecular Forces: Intermolecular forces are the attractive or repulsive forces that exist between molecules, which determine the physical and chemical properties of substances. These forces play a crucial role in the context of polar covalent bonds and dipole moments, as well as noncovalent interactions between molecules.
London Forces: London forces, also known as dispersion forces, are a type of van der Waals force that arise from the temporary, instantaneous dipole moments that can form in neutral atoms or molecules. These transient dipoles create an attractive force between nearby particles, even in the absence of permanent dipoles.
Polarity: Polarity is a fundamental concept in chemistry that describes the unequal distribution of electrons within a molecule or between atoms. This unequal distribution creates a separation of electrical charge, resulting in a molecule having a positive and negative end, known as a dipole moment.
Solvation: Solvation is the process by which solute particles or molecules become surrounded by solvent molecules, forming a solvated species. This interaction between the solute and the solvent is a crucial aspect of various chemical processes, including noncovalent interactions between molecules and the basicity of arylamines.
Specific Heat Capacity: Specific heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree Celsius or Kelvin. It quantifies a material's ability to store thermal energy and is an important property in understanding heat transfer and energy transformations between different substances.
Surface Tension: Surface tension is a property of liquids that arises from the cohesive forces between the surface molecules, causing the surface of a liquid to behave like an elastic sheet. This property is responsible for many phenomena observed in nature and is an important factor in various chemical and biological processes.
Van der Waals forces: van der Waals forces are weak intermolecular attractive forces that arise between neutral molecules. These forces, while individually weak, can collectively contribute to the physical and chemical properties of substances.