A dichromate ion has 56 valence electrons. Valence electrons are the electrons that are present in an atom which are responsible or allows the formation of a chemical bond. When you draw the lewis structure of a dichromate ions, you will have to calculate the valence electrons by (6 + 6 + 6 + 6 + 6 + 6 + 6 + 6 + 6 ) – (-2) = 56.
