The dichromate ion, Cr2O72-, has neither Cr¬Cr nor O¬O bonds. (b) How many outer-shell electrons does each Cr atom have in your electron-dot structure? What is the likely geometry around the Cr atoms?

Key Concepts

Electron Configuration

The electron configuration of an atom describes the distribution of its electrons among the various orbitals. For chromium (Cr), the electron configuration is [Ar] 3d5 4s1, indicating that it has six outer-shell electrons in its valence shell. Understanding this configuration is essential for determining the number of outer-shell electrons in the dichromate ion.

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms and the lone pairs of electrons in a molecule. In the case of the dichromate ion, drawing the Lewis structure helps visualize the arrangement of electrons around the chromium atoms, which is crucial for answering how many outer-shell electrons each Cr atom has.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. The geometry around the chromium atoms in the dichromate ion can be predicted using VSEPR theory, which states that electron pairs will arrange themselves to minimize repulsion. In this case, the geometry is typically described as tetrahedral due to the presence of four oxygen atoms surrounding the chromium atoms.