Glossary
Coulomb's Law
A fundamental law stating that the force of attraction or repulsion between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Example:
Coulomb's Law explains why closer charges result in stronger attractions, which is relevant to the strength of various intermolecular forces.
Dipole-Dipole Interactions
Attractive forces that occur between polar molecules due to the attraction between the positive end of one molecule and the negative end of another.
Example:
In hydrogen chloride (HCl), the slightly positive hydrogen of one molecule is attracted to the slightly negative chlorine of another, forming dipole-dipole interactions.
Hydrogen Bonding
A particularly strong type of dipole-dipole interaction that occurs when hydrogen is directly bonded to a highly electronegative atom (F, O, or N) and is attracted to a lone pair on another F, O, or N atom.
Example:
The high boiling point of water is primarily due to extensive hydrogen bonding between its molecules.
Intermolecular Forces (IMFs)
Attractive or repulsive forces that exist *between* molecules, influencing physical properties like boiling points and solubility.
Example:
The relatively high boiling point of water is due to strong intermolecular forces (specifically hydrogen bonds) between its molecules.
Intramolecular Forces
Strong attractive forces that exist *within* a molecule, holding atoms together through chemical bonds.
Example:
The covalent bond between hydrogen and oxygen atoms in a single water molecule is an intramolecular force.
Ion-Dipole Forces
Attractive forces that occur between an ion and a polar molecule, where the ion is attracted to the oppositely charged end of the polar molecule's dipole.
Example:
When sodium chloride (NaCl) dissolves in water, the Na+ ions are surrounded by water molecules through ion-dipole forces.
Ion-Ion Attractions
The strongest type of electrostatic attraction, occurring between oppositely charged ions in an ionic compound, holding them in a crystal lattice.
Example:
The strong forces holding Na+ and Cl- together in solid table salt are ion-ion attractions.
London Dispersion Forces (LDFs)
The weakest type of intermolecular force, arising from temporary, instantaneous dipoles caused by the momentary uneven distribution of electrons.
Example:
Even nonpolar molecules like methane (CH4) experience London Dispersion Forces due to the constant motion of their electrons.
Nonpolar Molecule
A molecule that does not have a net dipole moment, either because its bonds are nonpolar or because its polar bonds are symmetrically arranged and cancel each other out.
Example:
Carbon dioxide (CO2) is a nonpolar molecule despite having polar C=O bonds, as its linear geometry causes the bond dipoles to cancel.
Permanent Dipole
A persistent separation of charge within a molecule, resulting from an uneven distribution of electron density due to differences in electronegativity.
Example:
Water (H2O) is a polar molecule with a permanent dipole because oxygen is more electronegative than hydrogen, pulling electrons towards itself.
Polar Molecule
A molecule that has a net dipole moment due to the uneven sharing of electrons in its covalent bonds and an asymmetrical molecular geometry.
Example:
Ammonia (NH3) is a polar molecule because of its trigonal pyramidal shape and the electronegativity difference between nitrogen and hydrogen.
Polarizability
The ease with which the electron cloud of an atom or molecule can be distorted to form a temporary or induced dipole.
Example:
Larger molecules with more electrons, like iodine (I2), have higher polarizability and thus stronger London Dispersion Forces.
Temporary Dipole
A transient, instantaneous separation of charge within an atom or molecule, caused by the random movement of electrons.
Example:
When electrons in a helium atom momentarily shift to one side, they create a temporary dipole that can induce a dipole in a neighboring atom.