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  2. Aufbau principle - Wikipedia

    en.wikipedia.org/wiki/Aufbau_principle

    For example, in copper 29 Cu, according to the Madelung rule, the 4s subshell (n + l = 4 + 0 = 4) is occupied before the 3d subshell (n + l = 3 + 2 = 5). The rule then predicts the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 6 3d 9 4s 2, abbreviated [Ar] 3d 9 4s 2 where [Ar] denotes the configuration of argon, the preceding noble gas.

  3. Particle in a box - Wikipedia

    en.wikipedia.org/wiki/Particle_in_a_box

    The energy levels increase with , meaning that high energy levels are separated from each other by a greater amount than low energy levels are. The lowest possible energy for the particle (its zero-point energy ) is found in state 1, which is given by [ 10 ] E 1 = ℏ 2 π 2 2 m L 2 = h 2 8 m L 2 . {\displaystyle E_{1}={\frac {\hbar ^{2}\pi ^{2 ...

  4. 18-electron rule - Wikipedia

    en.wikipedia.org/wiki/18-electron_rule

    In the case of nickelocene, the extra two electrons are in orbitals which are weakly metal-carbon antibonding; this is why it often participates in reactions where the M–C bonds are broken and the electron count of the metal changes to 18. [9] The 20-electron systems TM(CO) 8 − (TM = Sc, Y) have a cubic (O h) equilibrium geometry and a ...

  5. Principal quantum number - Wikipedia

    en.wikipedia.org/wiki/Principal_quantum_number

    In a simplistic one-electron model described below, the total energy of an electron is a negative inverse quadratic function of the principal quantum number n, leading to degenerate energy levels for each n > 1. [1] In more complex systems—those having forces other than the nucleus–electron Coulomb force—these levels split.

  6. Dyck language - Wikipedia

    en.wikipedia.org/wiki/Dyck_language

    The number of distinct Dyck words with exactly n pairs of parentheses is the n-th Catalan number. Notice that the Dyck language of words with n parentheses pairs is equal to the union, over all possible k, of the Dyck languages of words of n parentheses pairs with k innermost pairs, as defined in

  7. Python syntax and semantics - Wikipedia

    en.wikipedia.org/wiki/Python_syntax_and_semantics

    Numeric literals in Python are of the normal sort, e.g. 0, -1, 3.4, 3.5e-8. Python has arbitrary-length integers and automatically increases their storage size as necessary. Prior to Python 3, there were two kinds of integral numbers: traditional fixed size integers and "long" integers of arbitrary size.

  8. Pumping lemma for regular languages - Wikipedia

    en.wikipedia.org/wiki/Pumping_lemma_for_regular...

    The proof that the language of balanced (i.e., properly nested) parentheses is not regular follows the same idea. Given p {\displaystyle p} , there is a string of balanced parentheses that begins with more than p {\displaystyle p} left parentheses, so that y {\displaystyle y} will consist entirely of left parentheses.

  9. Positronium - Wikipedia

    en.wikipedia.org/wiki/Positronium

    The branching ratio for o-Ps decay for this channel is 6.2 × 10 −18 (electron neutrino–antineutrino pair) and 9.5 × 10 −21 (for other flavour) [3] in predictions based on the Standard Model, but it can be increased by non-standard neutrino properties, like relatively high magnetic moment.