Chemistry: Electronic Structure, Periodic Trends, Bonding, and Molecular Formulas

Comprehensive vocabulary flashcards covering atomic structure, electron configurations, PES, periodic trends, bonding, nomenclature, empirical/molecular formulas, Lewis structures, and octet exceptions.

Aufbau Principle

A fill-up convention for adding electrons to orbitals in an atom stepwise across the periodic table, filling orbitals in order of increasing potential energy ($PE$).

Pauli Exclusion Principle

The quantum mechanical principle stating that no two electrons in an atom can have the exact same set of four quantum numbers.

Hund's Rule

The rule stating that electrons fill degenerate orbitals singly with parallel spins before pairing up with an opposite spin.

Stern-Gerlach Experiment

An experiment demonstrating that electrons possess magnetic spin; when a beam of atoms with unpaired electrons passes through an external magnetic field, it splits into spin-up and spin-down states.

Shell Model

An atomic model showing nuclear charge and energy levels (shells) with electrons arranged in concentric rings around the nucleus, without depicting subshells ($s, p, d, f$).

Effective Nuclear Charge ($Z_{\text{eff}}$)

The net positive nuclear charge experienced by valence electrons, roughly approximated as the total nuclear charge ($Z$) minus core shielding electrons ($S$).

Photoelectron Spectroscopy (PES)

An analytical technique that measures the relative number of electrons and their average binding/potential energies ($\Delta U_E$) to visualize orbital electron arrangements.

Scandium Photoelectron Spectrum

The experimental PES spectrum showing binding energy peaks for scandium: $433\,\text{MJ/mol}$ ($1s^2$), $48.5\,\text{MJ/mol}$ ($2s^2$), $39.2\,\text{MJ/mol}$ ($2p^6$), $5.44\,\text{MJ/mol}$ ($3s^2$), $3.24\,\text{MJ/mol}$ ($3p^6$), $0.77\,\text{MJ/mol}$ ($3d^1$), and $0.63\,\text{MJ/mol}$ ($4s^2$).

Electronegativity (EN)

An atom's tendency to attract and hang onto its valence electrons or pull on a shared bonded pair within a compound.

Metallic Character (MC)

The tendency of an atom to hold onto its valence electrons less fiercely, which increases as electronegativity decreases.

Electron Affinity (EA)

The energy change associated with adding an electron to a neutral gaseous atom to form an anion ($\text{Atom} + 1e^- \rightarrow \text{Anion}$).

Atomic Radius Trend

A periodic trend where atomic size decreases across a period due to increasing nuclear attraction at similar distances, and increases down a group due to the addition of electron shells.

Cationic Radius

The radius of a positive ion, which is smaller than its neutral atom because the loss of valence electrons increases $Z_{\text{eff}}$ and the inward attractive force on remaining electrons.

Anionic Radius

The radius of a negative ion, which is larger than its neutral atom because adding electrons increases inter-electron repulsion while $Z_{\text{eff}}$ remains unchanged.

Ionic Bonding

A type of chemical bonding typically occurring between metals and nonmetals with a large $\Delta\text{EN}$, forming a crystal lattice where valence electrons are localized on anions.

Covalent Bonding

A type of chemical bonding typically between nonmetals with a small $\Delta\text{EN}$ and high electronegativity, where valence electrons are shared and localized between bonded atoms.

Metallic Bonding

A type of chemical bonding among metal atoms with low electronegativity, characterized by valence electrons delocalized freely across all atoms in the solid.

Classical Cation Suffixes (-ic / -ous)

Nomenclature rules where the suffix '-ic' indicates the cation with the higher charge state (e.g., cupric, $\text{Cu}^{2+}$) and '-ous' indicates the cation with the lower charge state (e.g., cuprous, $\text{Cu}^+$).

Oxyanion Suffixes (-ate / -ite)

Nomenclature rules where '-ate' designates the oxyanion containing more oxygen atoms (e.g., $\text{SO}_4^{2-}$, sulfate) and '-ite' designates the oxyanion containing fewer oxygen atoms (e.g., $\text{SO}_3^{2-}$, sulfite).

Oxyanion Prefixes (per- / hypo-)

Nomenclature modifiers used in extended oxyanion series, where 'per-' indicates the most oxygen atoms (e.g., $\text{ClO}_4^-$, perchlorate) and 'hypo-' indicates the fewest oxygen atoms (e.g., $\text{ClO}^-$, hypochlorite).

Hydrated Salt

An ionic compound containing a specific molar ratio of water molecules trapped within its crystal lattice (e.g., $\text{NiCl}_2 \cdot 6\text{H}_2\text{O}$, nickel(II) chloride hexahydrate).

Protic Acid

A molecule capable of acting as a source of a hydrogen ion ($\text{H}^+$) in an aqueous solution.

Binary Acid

An acid consisting of hydrogen bonded to a single other element, whose strength increases as the $\text{H}-\text{X}$ bond length increases and weakens (e.g., $\text{HF} < \text{HCl} < \text{HBr} < \text{HI}$).

Oxyacid

An acid containing hydrogen bonded to an oxyanion, whose acidic strength increases with the number of attached oxygen atoms or higher electronegativity of neighboring atoms.

Formula Mass

The total mass in $\text{g/mol}$ of a compound, calculated by summing the molar masses of each constituent atom in its chemical formula.

Percent Composition

The percentage of a sample's total mass contributed by a specific component element, calculated as $\frac{\text{mass part}}{\text{mass whole}} \times 100$.

Empirical Formula (EF)

The simplest chemical formula representing the lowest whole-number mole ratio of elements in a compound.

Molecular Formula (MF)

The formula that indicates the actual number of atoms of each element in a molecule, related to the empirical formula by $\text{MF} = n \times \text{EF}$.

Lewis Structure

A 2D structural diagram illustrating bonding within molecules or polyatomic ions using lines for shared electron pairs and dots for non-bonded electrons.

Formal Charge (FC)

A bookkeeping value estimating an atom's electric charge in a Lewis structure, calculated as $\text{FC} = \text{valence } e^- - \frac{1}{2}(\text{bonded } e^-) - (\text{non-bonded } e^-)$.

Bond Polarity

The asymmetric distribution of electron density in a covalent bond caused by differences in electronegativity, producing partial positive ($\delta^+$) and partial negative ($\delta^-$) charges.

Hypovalent

A state in which a central atom in a Lewis structure possesses fewer than eight valence electrons prior to forming multiple bonds.

Incomplete Octet

A stable Lewis structure configuration in which the central atom remains surrounded by fewer than eight valence electrons (e.g., boron in $\text{BF}_3$).

Free Radical

A reactive chemical species containing an odd total number of valence electrons that features at least one single unpaired electron (e.g., $\text{NO}_2$ or $\text{ClO}$).

Resonance Structures

Two or more valid Lewis structures for a single chemical species that differ only in the distribution and arrangement of delocalized electrons.

Resonance Hybrid

The true, weighted-average structure representing a resonance-stabilized species, featuring fractional bonds and delocalized charge across equivalent atoms.

Extended Octet

An expanded valence shell where a central element in Period 3 or beyond is surrounded by more than eight electrons using accessible, empty $d$-orbitals.