Compounds of copper(II) are generally colored, but compounds of copper(I) are usually colorless. Use crystal field theory to explain why this is true.

See explanation

Explanation:

The crystal field theory assumes the interaction between the central metal ion and ligands to be purely electrostatic.

The five d orbitals remain degenerate until they are surrounded by ligands which split the degeneracy of the d orbitals depending on the crystal fields formed to give either square planar, octahedral, tetrahedral or other kinds of crystal fields.

The electronic configuration of Cu II ion is 1s2 2s2 2p6 3s2 3p6 3d9. Its colour arises from an incomplete d orbital which makes d - d electron transition possible.

On the other hand, the electron configuration of copper I is  1s2 2s2 2p6 3s2 3p6 3d10. We can see that the d orbital is completely filled. Hence copper I ion has no color due to its completely filled d- orbitals

it needs two electrons in the first and eight to fill the second.

Explanation:

Because neon has two atomic shells, it needs two electrons in the first and eight to fill the second. Neon has a total of ten electrons which means two filled shells.