Unit 3 Module 1: Analyzing Molecular Structure & Intermolecular Forces

Flashcards covering intermolecular forces, polarizability, physical properties, energy ranges, and PEC diagram-based mixing predictions from Unit 3 Module 1.

Intermolecular Forces (IMFs)

Attractive or repulsive interactions between particles (atoms, molecules, or ions) whose strength varies with intermolecular distance.

Polarizability

A measure of how easily the electron cloud of an atom, molecule, or ion is distorted or polarized by the presence of neighboring charged particles.

Induced Dipole Moment

A temporary separation of positive and negative charge in a particle created when external electric charges distort its electron distribution.

Dispersion Forces

Intermolecular attractions caused by instantaneous, induced temporary dipoles between particles; they depend directly on polarizability and are present in all atoms and molecules.

Dipole-Dipole Forces

Attractive intermolecular forces between polar molecules arising from the electrostatic attraction of their permanent molecular dipole moments.

Hydrogen Bond

A strong, directional dipole-dipole intermolecular attraction occurring between a hydrogen atom covalently bonded to $N$, $O$, or $F$ and a lone pair on a nearby $N$, $O$, or $F$ atom.

Normal Boiling Point ($T_b$)

The temperature at which the vapor pressure of a liquid reaches atmospheric pressure ($1\,\text{atm}$).

Vapor Pressure

The pressure exerted by gas molecules that escape from the liquid surface into the gas phase by overcoming liquid-liquid intermolecular attractions.

Volatility

The tendency of liquid particles to escape into the vapor phase; substances with weaker intermolecular forces have higher vapor pressures and higher volatility.

Viscosity ($\eta$)

A fluid's resistance to flow; liquids with stronger intermolecular forces or extensive molecular contact flow more slowly and exhibit higher viscosity.

Branching Effect

The reduction in intermolecular contact surface area resulting from structural branches in hydrocarbon isomers, which lowers dispersion forces, boiling points, and viscosity.

Debye ($D$)

The standard unit used to measure electric dipole moment ($\mu$) in polar molecules.

Covalent Bond Energy Range

The typical energy required to break an intramolecular covalent bond, ranging from $200$ to $1000\,\text{kJ/mol}$.

Intermolecular Force Energy Range

The typical energy required to overcome intermolecular attractions between molecules, ranging from $0.05$ to $40\,\text{kJ/mol}$.

Ion-Dipole Interaction

An intermolecular interaction between a fully charged ion and a permanent molecular dipole, with a typical strength of $4 - 600\,\text{kJ/mol}$.

Ion-Induced Dipole Interaction

An intermolecular interaction between an ion and a non-polar molecule whose electron cloud is temporarily polarized by the ion, with an energy range of $3 - 15\,\text{kJ/mol}$.

Dipole-Induced Dipole Interaction

An attractive force between a polar molecule with a permanent dipole and a neighboring non-polar molecule with an induced dipole, with an energy range of $2 - 10\,\text{kJ/mol}$.

PEC Diagram

A diagram plotting Potential Energy ($E_p$) versus the Number of Configurations to determine the thermodynamic stability and miscibility of mixed versus unmixed states.

Potential Energy ($E_p$) in Mixing

A thermodynamic factor determined by the competing strengths of $A\text{-}A$, $B\text{-}B$, and $A\text{-}B$ intermolecular interactions; lower potential energy reflects stronger net attractive forces.

Number of Configurations

The number of distinct, equivalent spatial arrangements available to particles in a state; states with a higher number of configurations are statistically favored.

Miscibility

The capability of two or more substances to mix together in all proportions and form a homogeneous solution.

Exothermic Mixing

A mixing process where $A\text{-}B$ interactions are stronger than pure component attractions, releasing energy, decreasing potential energy, and resulting in a heat of mixing less than zero.

Endothermic Mixing

A mixing process where $A\text{-}B$ interactions are weaker than pure component interactions, absorbing energy ($\Delta H_{\text{mix}} > 0$); mixing can occur if driven by an increase in configurations, often favored at higher temperatures.

Hydrophilic Surface

A water-attractive surface that readily engages in favorable polar and hydrogen-bonding interactions with water molecules.

Hydrophobic Surface

A water-repellent surface that cannot engage in favorable dipole-dipole or hydrogen bonding interactions with water, causing water droplets to bead up.

Polar Covalent Bonding Criteria

Bonding between nonmetallic elements characterized by an electronegativity difference $\Delta\chi < 2.0$ and an average electronegativity $\chi_{\text{AV}} > 2.0$.