Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2013

Lecture Notes 25: 29 March

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Sodium Demonstration

Electronic Configurations & Periodicity, cont.

Ions

When an atom loses electrons we would expect it to lose its outermost electrons first. But which are outermost? Remember the "last added" electrons in the transition elements are in the d orbitals of the next outermost shell. The the d orbital electrons should not be the outermost electrons in an atom. Thus we will lose the s & p electrons first then the d electrons if any are present. If additional electrons are lost then we can go into the d shell. Examples: look at Periodic Chart and figure out configurations for Na ion, Ni 2+ ion and Fe 2+ ion,

Periodic Table of the Elements
   IA IIA IIIA IVA VA VIA VIIA VIIIA
   H  He
2 Li Be    B C N O F Ne
3 Na Mg IIIB IVB VB VI VIIB VIIIB IB IIB  Al Si P S Cl Ar
4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5  Rb Sr  Y Zr Nb Mo Tc Ru Rh Pd  Ag  Cd  In Sn Sb Te I  Xe
6  Cs  Ba Lu Hf Ta  W Re Os Ir  Pt Au  Hg Tl  Pb Bi Po At Rn
  s1 s2 d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 p1 p2 p3 p4 p5 p6

 

Symmetry considerations

It turns out that symmetry is a strong driving force in nature and symmetry considerations are a powerful tool for predicting how nature operates. This is important in predicting electronic configurations because when two electronic energy levels are close to each other, as in the 3d orbitals (highest energy in the 3 shell) and the 4s orbitals (lowest energy in the 4 shell), symmetry considerations can result in an electron preferring to "fill" the 3d orbital set, making it symmetrical, instead of going to the already symmetrical 4s orbital. This can be done in two ways: we can put one electron in each of the five d orbitals giving a spherical half-filled d orbital set, or we can put 2 electrons in each orbital. Examples: look at Periodic Chart and figure out configurations for Cr, Cu, Cu +1 ion, Zn +2 ion and Fe +3 ion,

Periodic Table of the Elements
   IA IIA IIIA IVA VA VIA VIIA VIIIA
   H  He
2 Li Be    B C N O F Ne
3 Na Mg IIIB IVB VB VI VIIB VIIIB IB IIB  Al Si P S Cl Ar
4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5  Rb Sr  Y Zr Nb Mo Tc Ru Rh Pd  Ag  Cd  In Sn Sb Te I  Xe
6  Cs  Ba Lu Hf Ta  W Re Os Ir  Pt Au  Hg Tl  Pb Bi Po At Rn
  s1 s2 d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 p1 p2 p3 p4 p5 p6

 

Paramagnetism

Atoms and compounds are paramagnetic when they have unpaired electrons. Recall that electron spin can be thought of as electrons behaving as tiny magnets, and the arrows we use in orbital filling diagrams corresponding to the direction of the magnetic poles.

As a result, atoms such as oxygen and iron will be paramagnetic and be attracted to a magnetic field. For example, oxygen has two unpaired electrons as seen in the orbital filling diagram: orbital filling diagram for oxygen, so it is paramagnetic. Similarly, iron is paramagnetic due to its unpaired d electrons:

Fe orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing six p electron  spin "arrows" with paired up and down orientations orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing six p electron  spin "arrows" with paired up and down orientations orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing six d electron spin "arrows" two paired with opposite orientation and four with unpaired down orientation
1s
2s
2p
3s
3p
4s
3d

Whereas zinc, with the d shell filled, is not paramagentic since it has no unpaired electrons:

Zn orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing six p electron  spin "arrows" with paired up and down orientations orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing six p electron  spin "arrows" with paired up and down orientations orbital diagram showing two s electron  spin "arrows" with up and down orientations orbital diagram showing ten d electron  spin "arrows" with paired up and down orientations
1s
2s
2p
3s
3p
4s
3d

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© R A Paselk

Last modified 29 March 2013