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  2. Hund's rule of maximum multiplicity - Wikipedia

    en.wikipedia.org/wiki/Hund's_Rule_of_Maximum...

    For example, the nitrogen atom ground state has three unpaired electrons of parallel spin, so that the total spin is 3/2 and the multiplicity is 4. The lower energy and increased stability of the atom arise because the high-spin state has unpaired electrons of parallel spin, which must reside in different spatial orbitals according to the Pauli ...

  3. Multiplicity (chemistry) - Wikipedia

    en.wikipedia.org/wiki/Multiplicity_(chemistry)

    Each has two electrons of opposite spin in the π* level so that S = 0 and the multiplicity is 2S + 1 = 1 in consequence. In the first excited state, the two π* electrons are paired in the same orbital, so that there are no unpaired electrons. In the second excited state, however, the two π* electrons occupy different orbitals with opposite spin.

  4. Aufbau principle - Wikipedia

    en.wikipedia.org/wiki/Aufbau_principle

    Electrons are assigned to subshells in order of increasing value of n + l. For subshells with the same value of n + l, electrons are assigned first to the subshell with lower n. A version of the aufbau principle known as the nuclear shell model is used to predict the configuration of protons and neutrons in an atomic nucleus. [1]

  5. Basis set (chemistry) - Wikipedia

    en.wikipedia.org/wiki/Basis_set_(chemistry)

    In theoretical and computational chemistry, a basis set is a set of functions (called basis functions) that is used to represent the electronic wave function in the Hartree–Fock method or density-functional theory in order to turn the partial differential equations of the model into algebraic equations suitable for efficient implementation on a computer.

  6. Three-center four-electron bond - Wikipedia

    en.wikipedia.org/wiki/Three-center_four-electron...

    This exercise generates the diagram at right (Figure 1). Three molecular orbitals result from the combination of the three relevant atomic orbitals, with the four electrons occupying the two MOs lowest in energy – a bonding MO delocalized across all three centers, and a non-bonding MO localized on the peripheral centers.

  7. Electron multiplier - Wikipedia

    en.wikipedia.org/wiki/Electron_multiplier

    Contrasting differences between discrete and continuous electron multipliers. An electron multiplier is a vacuum-tube structure that multiplies incident charges. [1] In a process called secondary emission, a single electron can, when bombarded on secondary-emissive material, induce emission of roughly 1 to 3 electrons.

  8. Intersystem crossing - Wikipedia

    en.wikipedia.org/wiki/Intersystem_crossing

    That is, the spin of the excited electron is still paired with the ground state electron (a pair of electrons in the same energy level must have opposite spins, per the Pauli exclusion principle). In a triplet state the excited electron is no longer paired with the ground state electron; that is, they are parallel (same spin). Since excitation ...

  9. Linnett double-quartet theory - Wikipedia

    en.wikipedia.org/wiki/Linnett_Double-Quartet_Theory

    The mutual repulsion of electrons with like spins, in accordance with the Pauli exclusion principle. Hence, electrons with like (parallel) spins tend to keep as far away from each other as possible by refusing to occupy the same spatial region, while electrons with unlike (antiparallel) spins can occupy the same spatial region.