Chapter 4 – Molecular Compounds: Key Vocabulary

Vocabulary flashcards covering bonding, structure, geometry, electronegativity, and naming from Chapter 4 on Molecular Compounds.

Covalent Bond

A chemical bond created when two non-metal atoms share one or more pairs of electrons.

Molecule

A discrete group of atoms held together by covalent bonds and acting as an independent unit.

Molecular Compound

A substance composed of molecules (non-metals only) rather than ions.

Ionic Bond

An electrostatic attraction between oppositely charged ions, typically formed by metals and non-metals.

Ionic Compound

A crystalline solid consisting of a lattice of cations and anions (e.g., NaCl).

Bond Length

The optimum distance between the nuclei of two bonded atoms where attractive and repulsive forces balance.

Diatomic Molecule

A molecule made of two identical atoms, such as H₂, N₂, or Cl₂.

Octet Rule

Tendency of main-group atoms to be surrounded by eight valence electrons in compounds.

Duet Rule

Rule stating that hydrogen attains stability with only two electrons (one bond).

Expanded Octet

Situation in which elements in period 3 or higher use vacant d-orbitals to hold more than eight valence electrons.

Single Bond

A covalent bond formed by one shared electron pair (σ bond).

Double Bond

A covalent bond formed by two shared electron pairs (one σ and one π bond).

Triple Bond

A covalent bond formed by three shared electron pairs (one σ and two π bonds).

Multiple Covalent Bond

Any double or triple bond created so atoms can achieve octet configurations.

Coordinate Covalent Bond

A covalent bond in which both electrons of the shared pair originate from the same atom.

Valence Electrons

Electrons in the outermost shell involved in bonding; equal to group number for main-group elements.

Lewis Structure

A drawing that shows covalent bonds as lines and lone-pair electrons as dots around atoms.

Structural Formula

A molecular representation displaying only the connections (lines) between atoms.

Molecular Formula

Notation showing the exact numbers and kinds of atoms in a single molecule (e.g., C₂H₆).

Lone Pair

A pair of valence electrons not involved in bonding and residing on one atom.

Electron Group (Charge Cloud)

A region of electron density around a central atom: single bond, multiple bond, or lone pair.

VSEPR Model

Valence-Shell Electron-Pair Repulsion theory used to predict 3-D molecular shapes from electron groups.

Bond Angle

The angle formed by three atoms connected by two bonds in a molecule.

Linear Geometry

Shape produced by two electron groups around a central atom; bond angle 180°.

Trigonal Planar Geometry

Shape produced by three electron groups; bond angles 120°.

Bent Geometry

Angular shape that results when one or two lone pairs occupy positions in a trigonal planar or tetrahedral arrangement.

Tetrahedral Geometry

Shape produced by four electron groups; bond angles 109.5°.

Trigonal Pyramidal Geometry

Shape with three bonds and one lone pair around a central atom; bond angle ~107°.

Electronegativity

The ability of an atom to attract shared electrons in a covalent bond; highest for fluorine (4.0).

Polar Covalent Bond

A covalent bond with unequal sharing of electrons, giving partial charges (ΔEN ≈ 0.5–1.9).

Nonpolar Covalent Bond

A covalent bond with nearly equal sharing of electrons (ΔEN ≤ 0.4).

Dipole

Separation of partial positive and negative charges within a polar bond or molecule.

Polar Molecule

A molecule whose shape and bond polarities create an overall dipole moment (e.g., H₂O).

Numerical Prefixes

The set of prefixes (mono-, di-, tri-, tetra-, penta-, etc.) used to indicate atom counts in binary molecular names.

Binary Molecular Compound Naming

System that uses prefixes plus an “-ide” ending on the second element (e.g., CO₂ = carbon dioxide).