Chemistry

Intermolecular Forces (IMF)

Attractive forces between particles in a substance, generally weaker than intramolecular forces.

Dipole-Dipole Forces

Attractive force between polar molecules formed by the separation of equal and opposite charges.

Hydrogen Bonding

Occurs when a hydrogen atom bonded to a highly electronegative atom attracts unshared electron pairs from neighboring atoms.

London Dispersion Forces

Forces arising from instantaneous and temporary dipoles due to electron motion, present in all atoms and molecules.

Viscosity

Resistance of a fluid to movement; increases with stronger intermolecular forces.

Boiling Point

Amount of kinetic energy needed to overcome attractions; increases with stronger intermolecular forces.

Molecular Polarity

Determined by the presence of partial charges within a molecule.

Bond Electronegativity Difference (BEND)

Used to determine polarity; AEN = 0 indicates nonpolar, AEN ≠ 0 indicates polar.

Linear Shape

A molecular shape with 2 electron domains (Examples: O₂, HCN).

Trigonal Planar Shape

A molecular shape with 3 electron domains (Example: BF₃).

Tetrahedral Shape

A molecular shape with 4 electron domains (Example: CH₄).

Trigonal Bipyramidal Shape

A molecular shape with 5 electron domains (Example: PCl₅).

Octahedral Shape

A molecular shape with 6 electron domains (Example: SF₆).

Electronegativity

A measure of the ability of an atom to attract shared electrons in a bond.

Polar Molecules

Molecules that have a net dipole due to the presence of polar bonds.

Nonpolar Molecules

Molecules that do not have a net dipole; all bonds are nonpolar.

Strength of London Dispersion Forces

Typically low, approximately 0.1-5 kJ/mol.

Strength of Dipole-Dipole Forces

Medium strength, approximately 5-20 kJ/mol.

Strength of Hydrogen Bonds

Medium-high strength, approximately 5-50 kJ/mol.

Inter vs Intra

Inter means between or among substances (intermolecular forces); intra means within a substance (intramolecular forces).

Example of Hydrogen Bonding in H₂O

Attraction between hydrogen atoms in one H₂O molecule and oxygen atoms in another.

Shape of H₂O

Bent shape caused by 4 electron domains with 2 bonding pairs and 2 lone pairs.

Factors influencing Viscosity

Increased viscosity corresponds to stronger intermolecular forces.

Examples of Polar Molecules

Adenine, thymine, cytosine, guanine—found in DNA.

Characteristics of Hydrogen Bonds

Represented by dotted lines, significant impact on boiling points.

Determining Polarity in Molecules

Using BEND to conclude polar or nonpolar status based on electronegativity.

Rank of Molecular Polarity: O₂, CO₂, HCl, HF

From least polar (O₂) to most polar (HF).

Interaction of Instantaneous Dipoles

Temporary fluctuations in electron density leading to attractive forces.

Factors affecting Boiling Point

Nature of intermolecular forces present in the substance.

Example of Trigonal Pyramidal Shape

Molecular arrangement with 4 electron domains and 3 bonding pairs, represented by NH₃.

Visualization methods for Molecular Shapes

Includes notation and three-dimensional models to represent molecular geometry.

VSEPR Theory

Theory explaining the arrangement of electron domains around a central atom.

Importance of Lone Pairs in Molecular Shape

Lone pairs influence the spatial arrangement of bonding pairs.

Instantaneous Dipoles' Role in Noble Gases

London Dispersion Forces are particularly significant due to temporary dipoles.

Example of Trigonal Planar Structures

BF₃ exhibits a trigonal planar shape with 3 electron domains.

Characteristics of Ionic Bonds vs. IMF

Ionic bonds are stronger than intermolecular forces, which are generally weaker.