Almost all phase-change memory materials (PCM) contain chalcogen atoms, and their chemical bonds have been denoted both as âelectron-deficientâ [sometimes referred to as âmetavalentâ] and âelectron-richâ [âhypervalentâ, multicentre]. The latter involve lone-pair electrons. We have performed calculations that can discriminate unambiguously between these two classes of bond and have shown that PCM have electron-rich, 3câ4e (âhypervalentâ) bonds. Plots of charge transferred between (ET) and shared with (ES) neighbouring atoms cannot on their own distinguish between âmetavalentâ and âhypervalentâ bonds, both of which involve single-electron bonds. PCM do not exhibit âmetavalentâ bonding and are not electron-deficient; the bonding is electron-rich of the âhypervalentâ or multicentre type.