Chapter 8: Bonding & Molecular Structure

Vocabulary flashcards covering chemical bonding, Lewis structures, electronegativity, formal charge, resonance, and VSEPR molecular geometries.

Covalent bond

A chemical bond where two or more electrons are shared by two atoms.

Bonding Pairs

Shared electrons between atoms in a Lewis structure.

Lone Pairs

Non-shared electrons in a Lewis structure.

Duet rule

A rule for hydrogen indicating it forms bonds until it has $2$ electrons, achieving the helium $(He)$ electron configuration.

Octet rule

A rule stating that atoms other than hydrogen form bonds until they possess $8$ valence electrons, achieving a noble gas configuration.

Double bond

A type of multiple bond where two atoms share two pairs of electrons.

Triple bond

A type of multiple bond where two atoms share three pairs of electrons.

Bond length

The distance between the nuclei of two covalently bonded atoms in a molecule, where the relative order is Triple bond < Double Bond < Single Bond.

Polar Covalent Bond

A bond characterized by the unequal sharing of electrons between atoms, resulting in electron-rich region ($\delta-$) and electron-poor region ($\delta+$).

Electronegativity

A measure of how strongly an atom attracts electrons within a bond; $F$ is the most electronegative element.

Percent Ionic Character

A measure of the polarity of a bond, where $100\%$ ionic indicates a full transfer of electrons and $100\%$ covalent indicates equal sharing.

Terminal Atoms

Atoms bonded to only one other atom in a Lewis structure; typical examples include hydrogen and halogens.

Formal Charge

A calculation assigned to atoms in a Lewis structure using the formula: $\text{formal charge} = \text{Group \#} - \text{dots} - \text{lines}$.

Resonance structure

One of two or more Lewis structures for a single molecule that cannot be represented accurately by only one structure; the actual structure is a combination of all resonance structures.

Incomplete Octet

An exception to the octet rule where the number of electrons surrounding the central atom is less than $8$, common in beryllium $(Be)$, boron $(B)$, and aluminum $(Al)$.

Expanded valence shells

An exception to the octet rule where the central atom has more than $8$ electrons; possible for elements in the 3rd period and beyond such as $P$ and $S$.

VSEPR model

The Valence Shell Electron Pair Repulsion model, which predicts molecular shape based on the premise that electron pairs try to stay as far apart as possible.

Molecular Geometry

The specific arrangement of atoms around the central atom in a molecule.

Electron Domain Geometry

The arrangement of all electron domains (bonding and nonbonding) around the central atom.

Linear geometry

Geometry for type $AB_2$ molecules with a bond angle of $180^{\circ}$, such as $BeCl_2$.

Trigonal Planar Geometry

Geometry for type $AB_3$ molecules with bond angles of $120^{\circ}$, such as $BF_3$.

Tetrahedral Geometry

Geometry for type $AB_4$ molecules with bond angles of $109.5^{\circ}$, such as $CH_4$.

Trigonal Bipyramidal Geometry

Geometry for type $AB_5$ molecules featuring axial and equatorial positions with bond angles of $90^{\circ}$ and $120^{\circ}$.

Octahedral Geometry

Geometry for type $AB_6$ molecules with bond angles of $90^{\circ}$.

Bent Geometry

A molecular geometry variant occurring when there are lone pairs on the central atom, such as in $AB_2E$ (angle < $120^{\circ}$) or $AB_2E_2$ (angle < $109.5^{\circ}$).

Dipole Moment ($\mu$)

A quantitative measure of the polarity of a bond.

Polar molecule

A molecule that possesses a net dipole moment.

Nonpolar molecule

A molecule that does not have a net dipole moment, which occurs when bond dipoles cancel out.