AP Chemistry Unit 2 Notes: Chemical Bonding, Energy, and Solid Structure

Chemical bond

The attractive force that holds atoms or ions together in a stable structure; fundamentally based on electrostatic attraction between positive and negative charges.

Electrostatic attraction

Attraction between opposite charges (positive and negative); the underlying cause of ionic, covalent (nuclei–electron attraction), and metallic bonding.

Ionic bonding

Electrostatic attraction between cations and anions, typically forming an extended 3D lattice rather than discrete ion pairs.

Cation

A positively charged ion, formed when an atom loses one or more electrons.

Anion

A negatively charged ion, formed when an atom gains one or more electrons.

Ionic lattice

A repeating 3D crystal structure of alternating cations and anions where each ion is attracted to many oppositely charged neighbors.

Brittleness (ionic solids)

Tendency of ionic crystals to shatter when layers shift and like-charged ions become adjacent, causing strong repulsion and fracture.

Covalent bond

A bond in which atoms share electron density; both nuclei are attracted to the shared electrons.

Molecule

A discrete covalent unit made of specific atoms bonded together (e.g., H2O, CO2), often associated with lower melting points than ionic lattices.

Network covalent solid

A giant structure where atoms are covalently bonded in an extended network (e.g., diamond, SiO2), typically with very high melting points.

Polar covalent bond

A covalent bond with unequal sharing of electron density due to different electron-attracting ability, creating partial charges on the bonded atoms.

Electronegativity difference

A guideline for predicting bond character: large differences tend toward more ionic character, smaller differences toward more covalent character (bonding is a continuum).

Metallic bonding

Attraction between positively charged metal cores in a lattice and a sea of mobile, delocalized valence electrons; explains conductivity and malleability.

Electron-sea model

Model of metals where valence electrons are delocalized and shared throughout the metal, surrounding metal cores and enabling charge/energy flow.

Delocalized electrons

Valence electrons in metals that are not attached to any single atom and can move through the solid, enabling electrical and thermal conductivity.

Malleability

Ability of a metal to be hammered or pressed into shape without breaking, due to non-directional metallic bonding and electron mobility.

Ductility

Ability of a metal to be drawn into a wire, enabled by metallic layers sliding while delocalized electrons maintain attraction.

Intramolecular force

A strong force that holds atoms together within a particle or solid structure (ionic attractions, covalent bonds, metallic bonding), stronger than intermolecular forces.

Potential energy curve (bonding)

A graph of potential energy vs. distance showing attraction lowering energy and short-range repulsion raising energy, producing a “well” with a minimum.

Equilibrium bond length

The distance at which potential energy is minimized and net force is zero (attraction and repulsion balance), giving the most stable arrangement.

Bond dissociation enthalpy (bond energy)

Energy required to break one mole of a specific covalent bond in the gas phase; bond breaking is endothermic and bond formation is exothermic.

Coulomb’s law (ionic interactions)

Electrostatic force depends on charge and distance: F ∝ (q1q2)/r^2; stronger attraction occurs with larger charges and smaller separation.

Lattice energy

Energy associated with forming an ionic solid from gaseous ions (or the reverse, depending on convention); larger magnitude indicates stronger ion–ion attractions, increasing with higher charges and smaller ion sizes.

Substitutional alloy

An alloy where atoms of a second element replace some metal atoms in the lattice (e.g., Zn substituting into Cu in brass), disrupting regular packing and altering properties.

Interstitial alloy

An alloy where small atoms occupy holes between metal atoms (e.g., C in Fe to make steel), hindering layer movement and often increasing hardness/strength.