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Electron Configurations . Of Atoms & Ions. Men & their Rules. Aufbau Principle: Start at the beginning (Electrons enter lowest energy level 1 st ) Pauli Exclusion Principle: Only 2 allowed (Only 2 electrons allowed in any orbital) Hund’s Rule: Stay solo as long as possible
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Electron Configurations Of Atoms & Ions
Men & their Rules • Aufbau Principle: Start at the beginning (Electrons enter lowest energy level 1st) • Pauli Exclusion Principle: Only 2 allowed (Only 2 electrons allowed in any orbital) • Hund’s Rule: Stay solo as long as possible (For orbitals of equal energy, 1 electron enters each until all orbitals contain one before any pairs up.)
Consequences of Aufbau Principle • Electrons enter orbitals in order of increasing energy levels. • This order is shown in text on page 111. • 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p But there are two exceptions, namely Cu & Cr, who subtract 1 from 4s and add it to 3d.
Consequences of Pauli exclusion • The s orbital is filled with 2 electrons. • The 3 different orientations of the p orbital, px, py, & pz, each contain a max of 2 electrons • The 5 different orientations of d orbitals, dxy dxz, dyz, dx2-y2, & dz2, can have max of 2 each. • The 7 different orientations of f orbitals also only have 2 electrons for each suborbital.
Consequences of Hund’s Rule • One electron is added to px, then 1 to py, then 1 to pz, before the second one is added to px. The 5th electron is then added to py, & 6th to pz. • The same pattern is observed for the d & f suborbitals. • NOTE: The single electrons all have parallel spins. When the 2nd electron is added to each suborbital, it spins in the opposite direction.
Relating this to the periodic table: • The “s block” = Groups IA & IIA • The “p block” = Groups IIIB – VIII (13-18) • The “d block” = Transition elements (Groups IIIA-IIB; Groups 3-12) • The “f block” = Rare earth metals
What this means… • You merely need to follow the periodic table to figure out electron configurations. • The block (s, p, d, & f) indicates where the last electrons go. • Follow the period numbers, 1-7, because these are your energy levels & then remember suborbitals penetrate differently. • d block starts at 3d; f block starts at 4f
How can we apply this? • Follow the periodic table numerically • 1s2 (takes you to He) 2s2 (to Be) 2p6 (to Ne) 3s2 (to Mg) 3p6 (to Ar) 4s2(to Ca) 3d1-3 (to V) *** • Cr (1st exception): 1s22s22p63s23p64s13d5 • Cu (2nd exception): 1s22s22p63s23p64s13d10 • Mn: 1s22s22p63s23p64s23d5 • Zn: 1s22s22p63s23p64s23d10 • Ga: 1s22s22p63s23p64s23d104px1
Applications, continued • La is beginning of the lanthanide series • 1s22s22p63s23p64s23d104p65s24d105p66s25d1 • The pattern slightly changes with Ce • 1s22s22p63s23p64s23d104p65s24d105p66s25d14f 1 • Pr puts it back on track • 1s22s22p63s23p64s23d104p65s24d105p66s24f 3 • This is because 4f and 5d are close in energies
Noble Gas Configurations • Instead of writing entire core electron configuration of the noble gas, one can abbreviate it [NG] & write only valence e- • Al: 1s22s22p63s23px1or [Ne]3s23px1 • Ag:1s22s22p63s23p64s23d104p65s24d9 or [Kr]5s24d9 • Am:1s22s22p63s23p64s23d104p65s24d105p66s24f 14 5d106p67s25f 7or [Rn] 7s25f 7 • Sg: [Rn]7s25f 146d4 86+2+14+4 =106= Sb atomic#
Orbital Notations • This shows all 4 quantum numbers • n (principle quantum #) = energy lvl 1,2,3... • l (angular momentum Q.N.) = shape s,p,d,f • m (magnetic Q.N.) = x, y, z for p, etc… • s (spin Q.N.) = +1/2 (cw) or -1/2 (ccw) shown as upward or downward arrows 16 8O ___ ___ ___ ___ ___ 1s 2s 2px y z
