LB 171 Lecture Notes - Lecture 16: Atomic Radius, Diamagnetism, Roman Numerals
20 Oct 2016
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Lb 171 session 12 & 13 for exam ii. Hund"s rule, cations & anions, and periodic trends. The most stable e- configuration maximizes # of unpaired e- spins: put single e- in empty orbitals before pairing, extra stability for a filled subshell. All magnetism is caused by unpaired e: paramagnetic: 1+ unpaired e-, attracted to magnetic field, diamagnetic: no unpaired e-, not attracted. Explains exceptions in e- configurations: ex. Cr has [ar] 4s^1 3d^5 instead of 4s^2 3d^4 bc more stable with max unpaired e: note that for transition (d-block) metal cations, e- will be lost in the outmost s subshell first. Co+2 is [ar]3d^7 not [ar] 4s^2 3d^5. Cations & anions are formed to achieve noble gas configuration (ngc) Ionic compounds are made up of a metal cation (positive) & nonmetal anion (negative: always electrically neutral, d-block elements have variable charge; indicate + charge w/ roman numeral. Size of atom, defined by outermost/valence e- shell.
