AP Chem Unit 2

Chemical Bond

A force of attraction between atoms or ions that holds them together in compounds.

Ionic Bond

A bond formed by the transfer of electrons from a metal to a nonmetal, resulting in oppositely charged ions held together by electrostatic attraction.

Covalent Bond

A bond formed by the sharing of electrons between two nonmetal atoms.

Polar Covalent Bond

A covalent bond in which electrons are shared unequally due to a difference in electronegativity between the two atoms.

Nonpolar Covalent Bond

A covalent bond in which electrons are shared equally; occurs between atoms of the same or very similar electronegativity.

Bond Dipole

The separation of charge in a polar bond, creating partial positive (δ+) and partial negative (δ–) ends.

Metallic Bonding

The electrostatic attraction between a lattice of positive metal ions and a surrounding "sea" of delocalized valence electrons.

Delocalized Electrons

Electrons not associated with any single atom or bond; responsible for electrical conductivity in metals.

Potential Energy Diagram (bond)

A graph of potential energy vs. internuclear distance showing the equilibrium bond length (minimum energy) and bond energy (energy to separate atoms).

Bond Length

The distance between the nuclei of two bonded atoms at minimum potential energy; shorter for higher bond orders.

Bond Energy (Bond Dissociation Energy)

The energy required to break a specific bond; higher for bonds with higher bond order.

Bond Order

The number of shared electron pairs in a bond (single = 1, double = 2, triple = 3); higher order = shorter and stronger bond.

Ionic Crystal

A 3D arrangement of cations and anions that maximizes attractions and minimizes repulsions; described by Coulomb's law.

Interstitial Alloy

An alloy where smaller atoms (e.g., carbon) occupy the spaces between larger atoms (e.g., iron in steel); harder and less malleable.

Substitutional Alloy

An alloy where atoms of similar size replace each other in the crystal lattice (e.g., zinc in copper to make brass).

Lewis Diagram (Lewis Structure)

A representation of a molecule showing all valence electrons as dots or lines; follows rules for octet satisfaction.

Octet Rule

Atoms tend to form bonds to achieve 8 valence electrons (with exceptions for H, which needs 2, and some third-row or higher elements).

Resonance

When two or more equivalent Lewis structures can be drawn for a molecule; the actual structure is a hybrid of all resonance structures.

Formal Charge

The hypothetical charge on an atom in a molecule assuming equal sharing of bonding electrons; used to select the best Lewis structure. Formal charge = (valence electrons) – (nonbonding electrons) – ½(bonding electrons).

VSEPR Theory

Valence Shell Electron Pair Repulsion; predicts molecular geometry based on electron pair repulsions around a central atom.

Electron Geometry

The 3D arrangement of all electron groups (bonding and lone pairs) around a central atom.

Molecular Geometry

The 3D arrangement of only the atoms in a molecule (ignoring lone pairs); examples: linear, trigonal planar, tetrahedral, trigonal pyramidal, bent.

Molecular Geometries List

Linear (2 bonding, 0 lone pairs), Trigonal Planar (3,0), Tetrahedral (4,0), Trigonal Pyramidal (3,1), Bent (2,1 or 2,2), Trigonal Bipyramidal (5,0), Seesaw (4,1), T-shaped (3,2), Octahedral (6,0), Square Pyramidal (5,1), Square Planar (4,2).

Bond Angle

The angle formed between two adjacent bonds; affected by lone pairs (which compress bond angles).

Dipole Moment (molecular)

The overall polarity of a molecule; present when bond dipoles do not cancel due to asymmetric geometry.

Hybridization

The mixing of atomic orbitals to form new hybrid orbitals; sp = 180°, sp² = 120°, sp³ = 109.5°.

Sigma (σ) Bond

A bond formed by end-to-end orbital overlap; all single bonds are sigma bonds; stronger than pi bonds.

Pi (π) Bond

A bond formed by side-to-side orbital overlap; present in double and triple bonds; prevents rotation around the bond.

Geometric Isomers

Molecules with the same connectivity but different spatial arrangements due to restricted rotation around a double bond.