Rubies are gemstones with a characteristic red color that are members of the cor

Question

Rubies are gemstones with a characteristic red color that are members of the corundum family. Corundum is a crystalline form of aluminum oxide (AI203) and in its pure form is colorless and transparent. In the crystal lattice, each Al3+ ion is surrounded by six O2- ions in a slightly distorted octahedron. Impurities in the lattice give rise to the beautiful colors observed. In rubies, the impurity atom is CrS+, which replaces the A13+ ions at about 1-3%. Shown at right is an absorption spectrum for ruby, where the observed transitions all arise from Cr3+ 1.2 1.0 O 0.8 0.6 e 0.4 0.2 0.0 200 300 500 600 700 800

Explanation / Answer

A) Cr has electronic configuration [Ar] 3d^4 4s^2

To get Cr^3+ chromium should lose 3 electrons.

Electronic configuration of Cr^3+ = [Ar] 3d^3

So number of d electrons in Cr^3+ = 3

B) peaks observed at 550nm and 400 nm

Energy in cm for 550nm = 1/(550*10^-7 cm)

= 1.82*10^4 cm-1

Energy in cm-1 for 400nm = 1/(400*10^-7 cm)

   = 2.5*10^4 cm-1

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