Orbital occupations connect atomic electronic structure with valence chemistry.
Key knowledge
Electron configurations represent orbital occupations in an approximate atomic description. Ground-state filling and Hund's rule guide many configurations, but closely spaced subshell energies produce exceptions. Valence occupations help organize chemical similarities among elements.
Conditions and scope
The scope is isolated multielectron atoms and their stated charge states, not every excited state or molecule.
A fixed filling diagram alone does not predict all configurations; configurations of ions need separate consideration.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Electron configurations represent orbital occupations in an approximate atomic description. Ground-state filling and Hund's rule guide many configurations, but closely spaced subshell energies produce exceptions. Valence occupations help organize chemical similarities among elements.
Valence occupations organize chemical similarities; filling rules have exceptions.
Continuum shape and spectral-line patterns constrain temperature, composition and the physical conditions in a stellar atmosphere. Line strengths depend on excitation, ionization and opacity as well as abundance. A spectral classification therefore cannot be read as a direct abundance measurement from a single line's strength.
In an octahedral crystal-field model, d orbitals separate into a lower t2g set and an upper eg set. For eligible electron counts, the competition between splitting and electron-pairing energy produces different spin occupations. Geometry and ligand interactions affect splitting; crystal-field electrostatics is an approximation to metal–ligand electronic structure.
Neutral-fragment and oxidation-state counting consistently allocate ligand and metal electrons when their conventions are used throughout. In ionic counting the metal d count is its group number minus oxidation state, with ligand donations added separately. The 18-electron pattern is useful for many transition-metal complexes, but a stable square-planar platinum(II) complex can have 16 electrons.