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 (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 s 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, p x, p y, & p z, each contain a max of 2 electrons The 5 different orientations of d orbitals, d xy d xz, d y z, d x 2 - y 2, & d z 2, 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 p x, then 1 to p y, then 1 to p z, before the second one is added to p x. The 5 th electron is then added to p y, & 6 th to p z. The same pattern is observed for the d & f suborbitals. NOTE: The single electrons all have parallel spins. When the 2 nd 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 –1s 2 (takes you to He) 2s 2 (to Be) 2p 6 (to Ne) 3s 2 (to Mg) 3p 6 (to Ar) 4s 2 (to Ca) 3d 1-3 (to V) *** –Cr (1 st exception): 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 –Cu (2 nd exception): 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 Mn: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 Zn: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 –Ga: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p x 1

Applications, continued La is beginning of the lanthanide series –1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 5d 1 The pattern slightly changes with Ce –1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 5d 1 4f 1 Pr puts it back on track –1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 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: 1s 2 2s 2 2p 6 3s 2 3p x 1 or [Ne]3s 2 3p x 1 Ag:1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 9 or [Kr]5s 2 4d 9 Am:1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 2 5f 7 or [Rn] 7s 2 5f 7 Sg: [Rn]7s 2 5f 14 6d =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 8 O ___ ___ ___ ___ ___ 1s 2s 2p x y z