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Lecture 8

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University of Toronto Mississauga
Thottackad Radhakrishnan

Lecture 8 Wednesday, 22 January, 2014 11:01 AM Lecture Topic: Hund's Rule of Maximum Multiplicity  Definition: ○ Electrons occupy degenerate orbitals singlyif possible ○ Electrons will occupy a set of degenerate orbitals with parallel spin as far as possible ○ But other combinationsare also possible, but they are of higher energy or excited states  An orbital can only hold two electrons and they must have opposite spin ○ Otherwise, the third or second electron would have the same 4 quantum numbers as an already existing electron in the atom ○ Would not obey the Pauli principle 3  Ex: for the 2p configuration: State Px Py Pz 3s Excited (against Hund's rule) ↑ ↓ ↑ ○ Excited (against Hund's rule) ↓ ↑ ↑ Ground (follows Hund's rule) ↑ ↑ ↑  Know the order of orbital energies Why does the ionization energy change the way it does with the nuclear charge?  A half-filled shell has higher ionization energy than a fully-filled shell  Excess energy is needed to removeit because of increased attraction ○ If a shell is very stable, excess energy is needed to removean electron ○ There is repulsion between the two electrons in an orbital together, so it's easier to removeone  However,a fully filled configuration is more stable than a bunch of half-filled orbitals 2 ○ Be has s completelyfilled and is stable ○ B has only one electron in 2p so it can be removedeasily ○ N has 2p half-filled and stable 4 ○ O has 2p and the 4th electron in px where there is already an electron, so it is easy to remove Shape of the periodic table  The periodic table is arranged by the quantum number of the outermostelectron ○ H and the alkali and alkali-earth metals are the s-block elements ○ p-block elementsinclude the noble gases, halogens, non-metals, and metalloids ○ Transiti
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