A reliable quantitative physical theory of high-T-c superconductivity is not yet available, partly because a suitable model of the chemical composition, structure, and bonding of high-T-c superconductors (HTSCs) does not exist. Here the basic premise required for such a model is presented: that in the normal state of HTSCs there are electrons trapped in metal-metal bonds. Detailed chemical formulae (i.e., including metal-metal bonding electrons) are obtained for the superconducting systems K3C60 and La2-xBaxCuO4-delta and interpreted in terms of donor-acceptor electron charge transfer.