Intermolecular Forces and Properties

Vocabulary flashcards reviewing intermolecular and intramolecular forces, molecular polarity rules, dispersion mechanisms, hydrogen bonding, ion-dipole attractions, and their relative strengths.

Intramolecular Forces

Interactions occurring within a single molecule that hold it together, with examples including ionic bonds, covalent bonds, and metallic bonds.

Intermolecular Forces

Forces of interaction that occur between two different molecules, such as London dispersion forces, dipole-induced dipole forces, dipole-dipole forces, hydrogen bonding, and ion-dipole forces.

Polar Molecule

A molecule that contains polar bonds and either has lone pairs of electrons on the central atom or has terminal atoms bonded to the central atom that are not identical elements.

Nonpolar Molecule

A molecule that contains only nonpolar bonds, or one in which all atoms attached to the central atom are identical and there are no lone pairs of electrons on the central atom.

Dipole-Dipole Force

An intermolecular interaction occurring between any two polar molecules that can be attractive or repulsive; molecules orient to maximize attraction, and the interaction's strength is directly related to the magnitude of the dipole.

Dipole-Induced Dipole Force

An always-attractive intermolecular force between a polar and a nonpolar molecule, occurring when the dipole of the polar molecule repels electrons in the nonpolar molecule to temporarily induce a slight dipole depending on orientation and proximity.

London Dispersion Forces (LDFs)

Interactions produced by random electron fluctuations that create temporary dipoles, which in turn induce temporary dipoles in adjacent molecules; they are exhibited by all molecules and are the primary interaction between nonpolar molecules.

Polarizability

A measure of how easily an electron cloud can disperse or distort; larger electron clouds are more polarizable, which leads to stronger London dispersion forces.

Halogen Boiling Point Trend

The progressive increase in boiling points from fluorine ($F_2$, boiling point $-188\,^\circ\text{C}$) to chlorine ($Cl_2$, boiling point $-29\,^\circ\text{C}$) and bromine ($Br_2$, boiling point $59\,^\circ\text{C}$), resulting from larger molecules having more polarizable electron clouds and stronger London dispersion forces.

Hydrogen Bonding

An unusually strong type of dipole-dipole interaction occurring between a hydrogen atom covalently bonded to a highly electronegative atom ($N$, $O$, or $F$) and a highly electronegative atom on another molecule (or within distant parts of the same molecule).

Bare Proton

The exposed hydrogen nucleus formed when a small hydrogen atom partially loses its electron to a strongly electronegative atom (such as oxygen), allowing it to interact strongly with electronegative atoms of neighboring molecules.

Ion-Dipole Interaction

An electrostatic attraction occurring when ionic compounds dissolve in aqueous solution and the dipole of water separates the ions (oxygen interacting with cations and hydrogen interacting with anions); it is stronger than hydrogen bonding.

Relative Strength of Intermolecular Forces

The standard hierarchy ranking intermolecular forces from strongest ($1$) to weakest ($5$): ion-dipole ($1$), hydrogen bonding ($2$), dipole-dipole ($3$), dipole-induced dipole ($4$), and London dispersion forces ($5$).