PY4080: Periodic Table, Reactivity, Molecular Shape, and Bonding

Comprehensive vocabulary flashcards covering periodic table trends, valence electrons, formal charge, free radical exceptions to the octet rule, VSEPR theory, and molecular geometry classifications from PY4080 lectures.

Valence Electrons

The electrons located in the outermost shell of an atom, represented as dots in Lewis symbols, with the number of valence electrons corresponding to the element's Group Number on the Periodic Table.

Valence Orbitals Formula

The mathematical rule stating that the total number of valence orbitals in a given row of the Periodic Table is given by $n^2$, where $n$ is the period/row number.

Octet Rule

The principle that atoms tend to gain, lose, or share electrons until they are surrounded by $8$ valence electrons, thereby attaining the stable electron configuration of the nearest noble gas.

Covalent Bonding

A form of chemical bonding where two or more non-metal atoms share pairs of valence electrons to achieve a stable octet.

Formal Charge

A calculated electron bookkeeping value equal to the number of valence electrons of an isolated atom minus the number of electrons assigned to that atom in a Lewis structure.

Radical

An atom or neutral compound that possesses an odd number of valence electrons (an unpaired electron in its outermost shell), making it inherently reactive and an exception to the octet rule.

Nitric Oxide ($\text{NO}$)

A biological radical molecule containing $11$ valence electrons that is synthesized by endothelial cells and signals smooth muscle relaxation to induce vasodilation.

Nitrate Esters

A class of angina medications (such as nitroglycerin and isosorbide-5-mononitrate) that degrade in vivo to release nitric oxide ($\text{NO}$).

Nitrogen Dioxide ($\text{NO}_2$)

A toxic gas radical containing $17$ valence electrons that serves as an exception to the octet rule and is utilized in nitric acid ($\text{HNO}_3$) synthesis.

Ground State Diradical

A term describing diatomic oxygen ($\text{O}_2$) in its lowest energy state, which naturally possesses two unpaired electrons and acts as an exception to the octet rule.

2S+1 Rule

A formula where $S$ represents total electron spin, used to evaluate electron spin multiplicity and distinguish between the singlet and triplet electronic states of oxygen.

VSEPR Theory

Valence Shell Electron Pair Repulsion theory; a structural model predicting molecular geometry and bond angles by counting electron domains around a central atom to minimize repulsive forces.

Electron Domain

A region around a central atom containing electron density, where single bonds, double bonds, triple bonds, and non-bonding lone pairs each count as a single electron domain.

Linear Geometry

A molecular geometry resulting from $2$ electron domains with no central lone pairs, yielding a bond angle of $180^\text{o}$ (e.g., $\text{CO}_2$, $\text{BeH}_2$).

Trigonal Planar Geometry

A flat molecular shape resulting from $3$ electron domains pointing toward the corners of an equilateral triangle around a central atom in one plane, with bond angles of $120^\text{o}$ (e.g., $\text{BH}_3$).

Tetrahedral Geometry

A three-dimensional molecular geometry formed by $4$ bonding electron domains distributed evenly around a central atom, with bond angles of $109.5^\text{o}$ (e.g., $\text{CH}_4$).

Trigonal Pyramidal Geometry

A molecular shape derived from $4$ electron domains ($3$ bonding pairs and $1$ lone pair) where the central atom sits above a triangular plane, with bond angles compressed to $107^\text{o}$ (e.g., $\text{NH}_3$).

Bent Geometry (Water)

A molecular shape derived from $4$ electron domains ($2$ bonding pairs and $2$ lone pairs) where strong lone pair repulsions bend the bonds, compressing the bond angle to $104.4^\text{o}$.

Period 3 Octet Expansion

The ability of third-period elements and beyond (such as $\text{P}$ and $\text{S}$) to accommodate more than $8$ valence electrons by utilizing empty $3d$ orbitals during chemical bonding.

Trigonal Bipyramidal Geometry

A molecular shape formed by $5$ electron domains around a central atom (e.g., $\text{PCl}_5$), consisting of axial positions perpendicular to three equatorial positions in a central plane.

Octahedral Geometry

A symmetrical molecular shape formed by $6$ electron domains pointing toward the six vertices of an octahedron around a central atom (e.g., $\text{SF}_6$), where all bond angles measure $90^\text{o}$.