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Name:  Margaret
Status: educator
Grade: 9-12
Location:DC
Country: N/A
Date: 11/7/2005


Question:
Does Cu+1 lose its s electron or d electrons? Most transition metals lose there s electrons when they form a cation. Copper(I) oxide is a black solid; is this considered a colored compound? If it is considered a colored compound, why is copper an exception to the rule of transition metals losing their s electrons?


Replies:
A number of issues are at play here: First, the outer electron configuration of [Cu(+1)] in the gas phase is (3d10). See:

http://physics.nist.gov/cgi-bin/ASD/energy1.pl

The configuration (3d9,4s) is some 22,000 cm^-1 or (~2.7 ev) higher in energy. Now if you look at the electron configuration(s) of neutral Cu in the gas phase [Cu(0)], there are numerous electron configurations all having nearly the same energy.

See:

http://physics.nist.gov/cgi-bin/ASD/energy1.pl.

Now when an atom is placed in a solid phase environment, such as, Cu(+1)oxide these states get "scrambled" and it is not possible to give a precise atomic electronic state or configuration to the atoms. In fact, the CRC Handbook of Chemistry and Physics lists the color of Cu2O as red-brown. The reason it appears "black" can arise from two possibilities (one or both): small particle size, and the broad absorption is so complete as to absorb all the visible light. In attempting to "make sense" out of chemical bonding, chemists too frequently do not warn the students that the "simple" bonding schemes we invent are idealizations and not absolutely accurate descriptions of what is happening in any given bonding situation. If you look in an intermediate Inorganic Chemistry text, you will find the topic "ligand field theory" discussed in detail. This is a model to take into account partly the effect of surrounding atoms on the energy levels of transition metal compounds. The bottom line is that the electrons of a given atom in a compound are affected by its neighbors in solids and solutions, and often an exact description is not possible or is at best very complicated.

Vince Calder



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