Organic Chemistry: Atomic Structure

Anion  -  An ion with a net negative charge.

Atomic orbital  -  An orbital that is associated with only one particular atom. This is in contrast to molecular orbitals, which are spread across a collection of atoms.

Aufbau principle  -  German for "building up", a systematic procedure for determining the electron configuration of any atom.

Cation  -  An ion with a net positive charge.

Degenerate orbitals  -  Orbitals with identical energies.

Electron affinity  -  The energy change in an atom when it gains an electron.

First ionization energy  -  The energy cost of removing one electron from an atom.

Hund's Rule  -  A rule which says that electrons prefer to go in separate orbitals when choosing between orbitals of the same energy, in order to half-fill orbitals.

Ion  -  Any atom or molecule with a net charge.

Ionic bond  -  Bonding interaction that results from electrostatic attraction between cations and anions.

Ionization energy  -  The energy it takes to remove an electron from an atom.

Isoelectronic  -  Description for two elemental species with the same electronic configuration.

Isotope  -  Atoms with the same number of protons (i.e. same atomic number) but a different number of neutrons.

Octet rule  -  The cardinal rule of bonding. The octet rule states that atoms gain stability when they have a full complement of 8 electrons in their valence shells.

Orbital  -  The region around an atom where an electron has a high probability of being found.

Pauli Exclusion Principle  -  States that no two electrons in an atom or molecule can have the same set of four quantum numbers n, l, m, and s .

Second ionization energy  -  The energy cost of removing a second electron from an atom.

Shell  -  A group of subshells of similar energy levels. 2 s and 2 p subshells occupy the same shell.

Shielding  -  When the attraction from the nucleus felt by one electron is lessened or blocked by intermediate electrons. Shielding can split degenerate orbitals. For example, since s -orbital electrons shield for p -orbital electrons and receive little shielding themselves, s -orbitals are usually of lower energy level than p -orbitals of the same shell.

Splitting  -  The breaking of degenerate orbitals within a shell in multi-electron atoms.

Subshell  -  Orbitals in an atom with the same energy; orbitals of the same subshell are of the same shape. p -orbitals are of the same subshell, while s -orbitals are of a separate subshell.

Uncertainty Principle  -  A tenet of quantum mechanics which says that the position and momentum of any particle cannot both be known precisely at the same time.

Valence electron  -  The electrons in the outermost energy shell of an atom. The configuration of these electrons determine the chemical properties of the element.

Valence shell  -  The highest energy shell in an atom. All interactions between atoms take place through the electrons of the valence shell.