When electrons are added to the outermost shell of a carbon atom, it forms?

Your question is not clear but if you can explain yourself i would be glad to .  just trying to : ))

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).