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Anion
An ion with a net negative charge.
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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.
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Aufbau principle
German for "building up", a systematic procedure for determining the electron configuration of any atom.
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Cation
An ion with a net positive charge.
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Degenerate orbitals
Orbitals with identical energies.
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Electron affinity
The energy change in an atom when it gains an electron.
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First ionization energy
The energy cost of removing one electron from an atom.
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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.
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Ion
Any atom or molecule with a net charge.
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Ionic bond
Bonding interaction that results from electrostatic attraction between cations and anions.
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Ionization energy
The energy it takes to remove an electron from an atom.
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Isoelectronic
Description for two elemental species with the same electronic configuration.
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Isotope
Atoms with the same number of protons (i.e. same atomic number) but a different number of neutrons.
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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.
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Orbital
The region around an atom where an electron has a high probability of being found.
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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.
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Second ionization energy
The energy cost of removing a second electron from an atom.
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Shell
A group of subshells of similar energy levels. 2s and 2p subshells occupy the same shell.
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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.
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Splitting
The breaking of degenerate orbitals within a shell in multi-electron atoms.
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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.
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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.
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Valence electron
The electrons in the outermost energy shell of an atom. The configuration of these electrons determine the chemical properties of the element.
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Valence shell
The highest energy shell in an atom. All interactions between atoms take place through the electrons of the valence shell.
