Chapter 5 chemistry: Chemical Bonding I - Drawing Lewis Structures and Determining Molecular Shapes

Comprehensive vocabulary flashcards covering Lewis structures, electronegativity, resonance, formal charges, bond metrics, and VSEPR molecular geometry from Chapter 5.

Lewis Theory

A bonding theory that emphasizes valence electrons to explain bonding, predict molecular stability, and determine molecular shape, size, and polarity.

Ionic Bond

A chemical bond formed between a metal and a nonmetal characterized by the transfer of electrons from one atom to another, resulting in cation–anion attraction.

Covalent Bond

A chemical bond formed between nonmetal atoms characterized by the sharing of valence electrons between the bonded atoms.

Metallic Bond

A type of chemical bonding between metal atoms in which electrons are pooled and shared communally across the metal lattice.

Polar Covalent Bond

A covalent bond between unlike atoms where electrons are shared unequally, creating a region of higher electron density ($\delta^-$) at one end and an electron-deficient region ($\delta^+$) at the other.

Electronegativity

The ability of an atom to attract bonding electrons to itself; it generally increases across a period from left to right and decreases down a group from top to bottom.

Dipole Moment ($\mu$)

A quantitative measure of bond or molecular polarity given by $\mu = (q)(r)$, where $q$ is charge magnitude and $r$ is the distance separating the charges; measured in Debyes ($\text{D}$).

Pure Covalent Bond

A covalent bond with an electronegativity difference ($\Delta\text{EN}$) of $0$, resulting in completely equal electron sharing between identical or equally electronegative atoms.

Nonpolar Covalent Bond

A covalent bond characterized by a small electronegativity difference ($\Delta\text{EN}$ of $0.1$ to $0.4$), where electron sharing is nearly equal.

Resonance

The delocalization of electrons across a molecule or polyatomic ion, represented by two or more valid Lewis structures that differ only in electron positions, stabilizing the overall species.

Resonance Hybrid

The actual intermediate structure of a molecule that exists as a composite or weighted blend of its individual contributing resonance structures.

Formal Charge

An electron bookkeeping method used to evaluate competing Lewis structures, calculated as: $(\text{valence } e^-) - (\text{nonbonding } e^-) - \frac{1}{2}(\text{bonding } e^-)$.

Expanded Octet (Hypervalency)

The accommodation of $10$, $12$, or more electrons in the valence shell of a central atom, possible only for period 3 or heavier $p$-block elements due to accessible $d$ orbitals.

Incomplete Octet (Hypovalency)

A condition where an atom stably forms compounds with fewer than eight valence electrons, such as hydrogen forming a duet ($2$ electrons) or boron stably accommodating $6$ valence electrons.

Bond Energy

The quantity of energy required in the gaseous state to break one mole of a specific chemical bond between two atoms.

Bond Length

The distance between the nuclei of two bonded atoms; for like atoms, higher bond order corresponds to shorter and stronger bonds.

VSEPR Theory

Valence Shell Electron Pair Repulsion theory; a model stating that valence electron groups around a central atom orient themselves as far apart as possible to minimize electrostatic repulsion.

Electron Group

A region of electron density around a central atom that repels other regions; each lone pair, single bond, double bond, triple bond, or single radical electron counts as one group.

Repulsive Force Hierarchy (VSEPR)

The relative strengths of repulsion among electron groups: Lone pair – lone pair (strongest) $>$ Lone pair – bonding pair $>$ Bonding pair – bonding pair (weakest).

Linear Geometry

The electron or molecular geometry that results when two electron groups arrange on opposite sides of a central atom with a bond angle of $180^\circ$.

Trigonal Planar Geometry

The electron geometry that forms when three electron groups arrange in the plane of an equilateral triangle around a central atom with bond angles of $120^\circ$.

Tetrahedral Geometry

The electron geometry formed when four electron groups arrange symmetrically in three dimensions around a central atom with ideal bond angles of $109.5^\circ$.

Trigonal Bipyramidal Geometry

The electron geometry formed by five electron groups arranged as two tetrahedra sharing a base, having axial ($90^\circ$ to base) and equatorial ($120^\circ$ separation) positions.

Axial Positions

The two positions situated directly above and below the central atom along the vertical axis in a trigonal bipyramidal geometry, separated by $90^\circ$ from equatorial atoms.

Equatorial Positions

The three positions situated within the central triangular plane of a trigonal bipyramidal geometry with $120^\circ$ separation, which offer more space and preferentially house lone pairs.

Octahedral Geometry

The electron geometry formed when six equivalent electron groups arrange around a central atom in the shape of two square-base pyramids base-to-base, with all adjacent bond angles equal to $90^\circ$.

Trigonal Pyramidal Shape

A molecular geometry resulting from four electron groups (three bonding pairs and one lone pair) with bond angles compressed to less than $109.5^\circ$ (e.g., $107^\circ$ in $\text{NH}_3$).

Bent Shape

A molecular geometry resulting from either three electron groups (two bonding, one lone pair; angle $< 120^\circ$) or four electron groups (two bonding, two lone pairs; angle $< 109.5^\circ$, e.g., $104.5^\circ$ in $\text{H}_2\text{O}$).

Seesaw Shape

A molecular geometry derived from five electron groups containing four bonding pairs and one equatorial lone pair, yielding axial angles $< 90^\circ$ and equatorial angles $< 120^\circ$.

T-shaped Geometry

A molecular geometry derived from five electron groups with three bonding pairs and two equatorial lone pairs, resulting in bond angles of less than $90^\circ$.

Square Pyramidal Shape

A molecular geometry derived from six electron groups consisting of five bonding pairs and one lone pair, yielding axial-to-equatorial bond angles of less than $90^\circ$.

Square Planar Shape

A molecular geometry derived from six electron groups consisting of four bonding pairs and two trans (opposite) lone pairs, with bond angles of exactly $90^\circ$.

Solid Wedge

A stereochemical drawing convention used in three-dimensional representations on paper to signify a chemical bond pointing outward, toward the viewer.

Hatched Wedge

A stereochemical drawing convention used in three-dimensional representations on paper to signify a chemical bond projecting backward, away from the viewer into the page.

Molecular Polarity

The net macroscopic polarity of a compound determined by the three-dimensional vector summation of its individual bond dipole moments.