S18E2 - Electron Configurations and Periodic Trends

Electron Configurations

These are covered in great detail in SECTION 7 - Quantum Mechanical View of the Atom and Periodicity, so we'll only review them briefly here today.

Electron Configuration = the arrangement of electrons in energy levels around an atomic nucleus.

The Diagonal Rule:

There are two common exceptions to the "Diagonal Rule" to be aware of...

  ➞  Chromium (Cr) = 24e^-  ,  1s²2s²2p⁶3s²3p⁶4s¹3d⁵
  ➞  Copper (Cu) = 29e^-  ,  1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰

NOTE - when drawing electron configurations for ions, electrons are removed from the 4s-orbital first, not the 3d-orbitals.

   ex:   Cu⁺ = 28e^-  ,  1s²2s²2p⁶3s²3p⁶3d¹⁰

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Before moving on, I want to point out that it's best to learn how to write electron configurations for atoms and ions simply by looking at the Periodic Table.

We talked about how to do that in SECTION 7, but remember:

 - "the d's are one behind the Period number"
 - "the f's are two behind the Period number"

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Oxidation Numbers

Oxidation numbers are also called "Oxidation States."

Most transition metals have more than 1 oxidation state, and these are usually the same as the metal's charge(s).

  ex:    Fe²⁺   ,   Fe³⁺
  ex:    Cr³⁺   ,   Cr⁶⁺

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Ionization Energy Trend

  ➞ was discussed thoroughly way back in SECTION 7.

Ionization Energy (I.E.)  =  the energy required to remove an electron from an atom:

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Atomic Radius Trend

In the image below, you'll see a very simplified, very generic Periodic Trend for Atomic Radius (or "Atomic Size")...

NOTES on the Periodic Trend for Atomic Radius:

1.  There's a significant increase in the size of atomic radius in going from the 3d → 4d (period 4 → period 5), but...

2.  There's a minimal increase (if any) in the size of atomic radius in going from the 4d → 5d (period 5 → period 6) transition series.

Why?? What's going on?

This is due to the "lanthanide contraction."

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Lanthanide Contraction

The 4f lanthanide orbitals (period 6) are buried in the atom's interior, so as the 14 electrons are added to the 4f-orbitals, additional electrons don't affect the atomic size.

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As we move forward and begin talking about Coordination Compounds and Complex Ions in my next post on SECTION 18 - Transition Metals and Coordination Compounds ...

It might help to review your textbook for some basic info about the following 3d metals (Period 4 transition metals):

Sc,  Ti,  V,  Cr,  Mn,  Fe,  Co,  Ni,  Cu,  Zn

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What's next?... My 3rd post of course!

You can find my third video blog entry on SECTION 18 - Transition Metals and Coordination Chemistry at the following link:

Complex Ions, Ligands, Coordination Number, and Coordination Compounds :-)