CHMA10H3 Lecture Notes - Lecture 23: Quantum Mechanics, Dmitri Mendeleev, Periodic Table

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CHMA10 Lecture 20: Finishing Quantum Mechanics
- Multi-Electron atoms: energy of sublevels (s, p, d, f) differs based on how far they are to
the nucleus
o Order of the energy of sublevels from least to greatest is as follows
E-s orbital, E-p orbital, E-d orbital, E-f orbital
The s orbital is closest to the nucleus compared with the other three
This is why it has the lowest energy ‘
o Hundt’s Rule: when filling degenerate orbitals, electrons will fill first with parallel
spins
Essentially states that we should always try and fill all compartments in
electron diagrams before pairing electrons
Noble Gas Shorthand: include configuration of the closest noble has plus
the valence electrons left over
- Transition Metals: refers to the 3d orbital lower in energy than the 4s orbital
o After a certain point elements will begin to prefer putting their electrons in s
orbitals over the d orbitals
o When making ions, we must always remove electrons from the highest n-values
first
Example
V = [Ar] 4s2 3d3
V2+ = [Ar]3d3
o We remove the 2 electrons from the 4s orbital
o The 3d orbitals are lower in energy than the 4s ones
However as electrons are added to the 3d, it rises in energy and
eventually exceeds the 4s level
This is why at a certain point, elements prefer to put electrons in the 4s
orbital over the 3d
o 2 exceptions seen with chromium and copper
Cr
Theoretical configuration = Cr: [Ar] 4s2 3d4
Actual configuration = Cr: [Ar] 4s1 3d5
In this special case, the 3d orbital fills instead of allowing the 4s to
pair electrons
o Now the 3d has more energy than the 4s
o The next electron added will go to the 4s before the 3d
Cu
Theoretical configuration = Cu: [Ar] 4s2 3d9
Actual configuration = Cu: [Ar] 4s1 3d10
In this special case, the 3d orbital gets fully filled before the 4s
orbital
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