  The second quantum revolution is all about exploiting the quantum nature of
atoms and molecules to execute quantum information processing tasks. To support
this growing endeavor and by anticipating the key role of quantum chemistry
therein, our work establishes a toolbox for systematically exploring,
quantifying and dissecting correlation effects in quantum chemical systems. By
utilizing the geometric picture of quantum states we compare -- on a unified
basis and in an operationally meaningful way -- total, quantum and classical
correlation and entanglement in molecular ground states. To maximize the
quantum informational resourcefulness of molecules an orbital optimization
scheme is provided, leading to a paradigm-shifting insight: A single covalent
bond equates to the entanglement $2\ln(2)$. This novel and more versatile
perspective on electronic structure suggests a generalization of valence bond
theory, overcoming deficiencies of modern chemical bonding theories.
