CHEM 102 Discussion: Chemical Bonding, Geometry, Hybridization, and Stoichiometry

Vocabulary practice flashcards covering Lewis structures, VSEPR molecular geometry, valence bond theory, orbital hybridization, chemical equation balancing, mole conversions, and stoichiometry concepts.

Bond Order

The number of shared electron pairs between two atoms; as bond order increases from single to triple, bond length becomes shorter and bond strength becomes stronger.

Formal Charge

The calculated charge of an atom in a molecule given by: $\text{Formal Charge} = \text{valence } e^- - \text{lone pair } e^- - \frac{1}{2}(\text{bonding } e^-)$.

Expanded Octet

A condition in which a central atom has more than eight valence electrons; permitted only for elements in row 3 and below of the periodic table.

Resonance

A phenomenon that occurs when more than one valid Lewis structure can be drawn for a molecule by shifting electrons (such as $\pi$ electrons and lone pairs) without moving any atomic nuclei.

VSEPR Theory

Valence Shell Electron Pair Repulsion theory; states that electron groups around a central atom repel one another and arrange themselves spatially as far apart as possible.

Electron Group

A region of high electron density around a central atom; every single bond, double bond, triple bond, or lone pair counts as exactly one electron group.

Electron Geometry

The three-dimensional geometric arrangement of all electron groups (including both chemical bonds and lone pairs) situated around the central atom.

Molecular Geometry

The spatial arrangement of the bonded atoms around a central atom; lone pairs influence the positions of the atoms but are not included in the geometry name.

Wedge and Dash Notation

A stereochemical drawing convention where a normal line indicates a bond lying in the plane of the page, a solid wedge indicates a bond pointing toward the viewer, and a dashed wedge indicates a bond pointing away.

Tetrahedral Geometry

The molecular geometry formed by four single bonds and zero lone pairs around a central atom, exhibiting bond angles of $109.5^\circ$ (e.g., $CH_4$).

Trigonal Bipyramidal Geometry

The molecular geometry observed when five bonding groups and zero lone pairs surround a central atom (e.g., $PCl_5$).

Octahedral Geometry

The molecular geometry featuring six bonding groups and zero lone pairs around a central atom, forming a square in the equatorial plane with axial atoms above and below at $90^\circ$ bond angles (e.g., $SF_6$).

Valence Bond (VB) Theory

A model of chemical bonding stating that a covalent bond forms when atomic orbitals on adjacent atoms overlap and share a pair of electrons with opposite spins.

Sigma ($\sigma$) Bond

A covalent bond produced by the head-on overlap of atomic or hybrid orbitals along the internuclear axis.

Pi ($\pi$) Bond

A covalent bond formed by the side-by-side overlap of parallel, unhybridized $p$ orbitals perpendicular to the bonding axis.

Orbital Hybridization

The process of mixing standard atomic orbitals (such as $s$ and $p$) on a central atom to create new equivalent hybrid orbitals oriented toward specific directions in space.

Steric Number

The total count of electron-density regions surrounding a central atom, calculated as $\text{Steric Number} = \#\sigma\text{ bonds} + \#\text{lone pairs}$, used to deduce hybridization.

Delocalized Pi Electrons

Electrons in unhybridized $p$ orbitals that extend across three or more adjacent atoms rather than being restricted to a localized two-atom bond (e.g., across the $O-O-O$ framework of ozone).

Law of Conservation of Mass

The principle stating that atoms cannot be created or destroyed in a chemical reaction; consequently, every element must maintain an equal number of atoms on both the reactant and product sides of a chemical equation.

Avogadro’s Number

The number of fundamental particles contained in one mole of a substance, defined as $N_A = 6.022 \times 10^{23}\,\text{mol}^{-1}$.

Molar Mass

The mass in grams of one mole of a substance ($\text{g/mol}$), calculated by summing the weighted average atomic masses of all atoms present in its chemical formula; it is not an exact value and obeys significant figure rules.

Limiting Reactant

The reactant in a chemical process that is entirely consumed first, thereby limiting and determining the maximum theoretical yield of products.

Excess Reactant

A reactant present in a quantity greater than required to completely react with the limiting reactant, leaving an unconsumed portion after the reaction stops.

Mole Ratio

A stoichiometric conversion factor derived directly from the whole-number coefficients of a balanced chemical equation that relates the molar amounts of two substances.