Final answer:
The ethylene dication (C2H4)2+ has 10 valence electrons, as a neutral ethylene molecule has 12 valence electrons, and the dication has lost two electrons.
Step-by-step explanation:
To determine how many valence electrons are in the ethylene dication (C2H4)2+, we start by counting the valence electrons in a neutral ethylene molecule, C2H4. Each carbon atom contributes 4 valence electrons, totaling 8 for the two carbon atoms. Each hydrogen atom contributes 1 valence electron, and since there are four hydrogen atoms, that's an additional 4 valence electrons. Thus, the neutral ethylene molecule has a total of 12 valence electrons.
When ethylene becomes a dication (C2H4)2+, it loses two electrons, reducing the total count of valence electrons. Consequently, the ethylene dication will have 10 valence electrons. The loss of electrons will likely alter the molecular orbital configuration and the molecule's stability, but strictly considering the valence electrons, the answer is 10.
In the context of the exercises and examples presented, determining the geometry and shape of the molecule and the electron configurations would depend on both the valence electron count and the molecular orbital theory. These are sophisticated concepts typically discussed in high school chemistry classes or introductory college chemistry courses.