Electron Configurations

Electron Configurations
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
• 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
• 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.
How can we apply this?
• In our upcoming lab we will observe metals
forming ions due to their electron
• Different metals (s vs. d vs. p) will behave
• Transition metal ions usually have color.
Setting up the lab
• Mark 3 grids as shown
on whiteboard, 3” x 4”.
• We do not have NiSO4;
place AgNO3 there
• We will use 4 glass
slides, 3 vertical & 1
• After you’ve observed
color of solutions, add
a drop of NaOH to
each & note changes.
• Repeat with addition
of Na2CO3.
• Write chemical
formulas for rxns.
Solutions for this lab:
1.0 M NaCl & Na2CO3
0.5 M CaCl2 & NaOH
0.2 M MgSO4, AlCl3, CuSO4, & ZnCl2
0.1 M FeCl3
0.05 M AgNO3
Lab Report
• You must answer all questions in handout.
• You must relate electron configurations to
what you observe & discuss this in the
Conclusions section.
• You can use the Internet to obtain extra
information concerning these reactions.