Atomic Structure, Periodic Trends, Bonding, and Thermochemistry

Vocabulary flashcards covering atomic structure, electron configurations, periodic trends, bonding, intermolecular forces, molecular shapes, and thermochemical heating curves.

Electron shell

An energy level found outside the nucleus where electrons reside, with each successive energy level adding an electron shell.

Electron subshell (sublevel)

A division of an electron shell into one of four quantum energy sublevels designated $s$, $p$, $d$, and $f$.

Orbital

A region within a subshell capable of holding up to $2$ electrons; the $s$ subshell has $1$ orbital, $p$ has $3$ orbitals, and $d$ has $5$ orbitals.

Electron spin

The property of electrons in an orbital to rotate in opposite directions, where orbitals first fill singly with parallel spins before electrons pair up.

Subshell filling order

The sequential order in which electrons fill sublevels from lowest to highest energy: $1s$, $2s$, $2p$, $3s$, $3p$, $4s$, $3d$, $4p$.

Chromium ($\text{Cr}$) electron configuration

An exceptional configuration of $1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1$ (or $[\text{Ar}]\,3d^5 4s^1$), where one $4s$ electron is promoted to achieve a more stable half-filled $3d$ subshell.

Copper ($\text{Cu}$) electron configuration

An exceptional configuration of $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^1$ (or $[\text{Ar}]\,3d^{10} 4s^1$), where one $4s$ electron is promoted to achieve a more stable fully filled $3d$ subshell.

Periods

Horizontal rows of the periodic table in which elements share the same number of electron shells, arranged from lowest energy electrons closest to the nucleus to highest energy electrons farthest away.

Groups

Vertical columns of the periodic table containing elements with the same number of valence electrons in their outermost shell.

Atomic radius

The distance from the atomic nucleus to the outermost electron, which decreases across a period and increases down a group.

Effective nuclear charge

The net positive electrostatic attraction exerted by the protons in the nucleus on surrounding electrons.

Shielding

The reduction in nuclear attraction experienced by valence electrons caused by electron-electron repulsions from inner electron shells.

Cation radius

Smaller than that of the neutral parent atom because the loss of outer electrons removes an outer shell and increases the effective nuclear charge pulling on remaining electrons.

Anion radius

Larger than that of the neutral parent atom because gaining electrons increases electron-electron repulsions while nuclear charge remains constant.

Ionisation energy

The energy required to remove the outermost, most loosely bound valence electron from $1\,\text{mol}$ of gaseous atoms or ions under standard conditions, measured in $\text{kJ}\,\text{mol}^{-1}$.

Boron vs. Beryllium ionisation energy anomaly

Boron has a lower first ionisation energy than Beryllium because Boron's outermost electron occupies a $2p$ subshell that is higher in energy and further from the nucleus than Beryllium's $2s$ subshell.

Nitrogen vs. Oxygen ionisation energy anomaly

Oxygen has a lower first ionisation energy than Nitrogen because its paired electrons in one of the $2p$ orbitals experience mutual repulsion, making removal easier than from Nitrogen's stable half-filled $p$ subshell.

Electronegativity

A measure of how strongly an atom attracts bonding electrons to itself, increasing across a period and decreasing down a group.

Expanded octet

The ability of Period $3$ and higher elements to accommodate more than $8$ valence electrons by promoting electrons into vacant, accessible $3d$ subshells.

Ionic bonding

The electrostatic attraction between oppositely charged cations and anions arranged in a rigid, non-malleable lattice structure.

Metallic bonding

The non-directional electrostatic attraction between fixed positive metal cations and a surrounding mobile sea of delocalised electrons.

Temporary dipole-dipole attractions

Weak, short-lived intermolecular forces arising from unsymmetrical fluctuations in electron clouds that induce dipoles in neighbouring molecules.

Permanent dipole-dipole attractions

Intermolecular electrostatic attractions that occur between polar molecules possessing permanent molecular dipoles.

Hydrogen bonding

The strongest intermolecular force, formed when hydrogen is covalently bonded to highly electronegative nitrogen, oxygen, or fluorine ($\text{N}$, $\text{O}$, or $\text{F}$) and attracted to a lone pair on an adjacent molecule.

Covalent network

A large macromolecular lattice of atoms linked throughout by strong covalent bonds (e.g., diamond, graphite, $\text{SiO}_2$), resulting in high melting points and insolubility.

Phase change plateau

A horizontal region on a heating curve where temperature remains constant because added heat energy is used to break or overcome intermolecular forces rather than increase molecular kinetic energy ($E_k$).

Transition metal colour origin

The appearance of colour in transition metal compounds resulting from partially filled $3d$ orbitals absorbing specific wavelengths of visible light and transmitting the remaining spectrum.