Molecular Geometry – Key Vocabulary (Unit 5 Part 4)

30 vocabulary flashcards summarizing the essential terms and definitions from the Unit 5 Part 4 lecture on VSEPR-based molecular geometry.

Lewis Structure

A 2-D diagram that shows valence electrons as dots or lines; serves as the starting point for predicting 3-D molecular geometry.

VSEPR Model

Valence Shell Electron Pair Repulsion theory; predicts molecular shape by assuming electron domains repel and arrange as far apart as possible.

Electron Domain

Any region of electron density (bond or lone pair) around an atom that is counted to determine geometry.

Bonding Domain (BD)

An electron domain created by a bond to another atom; single, double, and triple bonds each count as one BD.

Nonbonding Domain (NBD)

A lone pair of electrons on an atom; counts as one electron domain but is not involved in bonding.

Ideal Angle

The predicted angle between electron domains for a given total number of domains, assuming equal repulsion.

Linear Geometry

Shape with two bonding domains around a central atom; ideal bond angle = 180°.

Trigonal Planar Geometry

Flat, three-atom arrangement with three bonding domains; ideal bond angle = 120°.

Bent (3 Domains)

Shape produced by two bonding and one nonbonding domain (three total); ideal angle = 120°.

Tetrahedral Geometry

Arrangement of four bonding domains around a central atom in 3-D; ideal bond angles = 109.5°.

Trigonal Pyramidal Geometry

Shape resulting from three bonding and one lone-pair domain (four total); looks like a pyramid with triangular base; ideal angle = 109.5°.

Bent (4 Domains)

Shape with two bonding and two lone-pair domains (four total); ideal angle = 109.5°.

Tetrahedron

A 3-D solid with four equilateral triangular faces; models the arrangement of four electron domains.

Central Atom

An atom bonded to at least two other atoms and to which a geometry name is assigned.

Bond Angle

The angle between two bonding domains on a central atom.

Resonance

Multiple valid Lewis structures for the same molecule that share the same geometry.

Valence Shell

The outermost electron shell of an atom containing the electrons involved in bonding.

Molecular Geometry

The three-dimensional arrangement of atoms (and lone pairs) around a central atom.

Electron Domain Counting Rule

Guideline that each single, double, or triple bond counts as one domain when predicting geometry.

180° Angle

Ideal angle for atoms with two total electron domains (linear geometry).

120° Angle

Ideal angle for atoms with three total electron domains (trigonal planar or bent).

109.5° Angle

Ideal angle for atoms with four total electron domains (tetrahedral, trigonal pyramidal, or bent).

Planar Molecule

A molecule in which all atoms lie in the same plane, e.g., trigonal planar shapes.

3-D Wedge-Dash Notation

Drawing method using solid wedges (coming toward) and dashed wedges (going away) to depict spatial orientation.

Valence Shell Electron Pair Repulsion (full term)

The concept that electron pairs in the valence shell orient to minimize repulsive forces, dictating molecular shape.

Polarity Determination (preview)

Assessing whether a whole molecule is polar or nonpolar by combining geometry with bond dipoles (next lecture topic).

d Orbitals (note)

Orbitals involved when an atom has more than four electron domains; beyond the scope of this course’s geometry coverage.

Geometry Name Assignment

Choosing a shape name based on the number of bonding and nonbonding domains around a central atom.

Skeleton Drawing

Step-by-step sketch: draw central atom, add sticks at ideal angles, then attach atoms and lone pairs.

Ideal vs. Actual Angles

Ideal angles are theoretical; real angles deviate due to lone-pair repulsion or multiple-bond effects.