The known electronic states of diatomic hydride molecules (MH) are derivable from unexcited H plus familiar low-energy states of M atoms (Hund, Hulth\'en, Mecke, Mulliken: cf. Table I). Observed states, and \`especially observed $\ensuremath{\Delta}\ensuremath{\nu}$ intervals in $^{2}\ensuremath{\Pi}$ or $^{3}\ensuremath{\Pi}$ states of such MH molecules (cf. Table III), indicate that the effects of the H on the M atom are confined essentially to the following: (1) the couplings, when present, between ${l}_{\ensuremath{\tau}}$ vectors of M atom outer electrons to give a resultant $l$ are completely broken down by the field of the H nucleus; the M atom orbits are otherwise scarcely changed, except for slight shielding or similar effects produced by the H electron and nucleus; the usual ${l}_{\ensuremath{\tau}}$ selection rules are, however, abolished; (2) the uncoupled vectors ${l}_{\ensuremath{\tau}}$ are separately space-quantized with reference to the electric axis, giving component quantum numbers ${i}_{l\ensuremath{\tau}}$; (3) the electron of the H atom (${i}_{l\ensuremath{\tau}}=0$) is promoted and takes its place with the M electrons, sometimes becoming equivalent to one of them giving a new closed shell (of two electrons); the H nucleus, however, stays on the outside edge of the M electron cloud, so that the hydrides should in general be strongly polar, in agreement with Mecke's conclusions: (4) the original couplings of ${s}_{\ensuremath{\tau}}$ vectors are often broken down by the advent of the H electron spin; always, the latter alters the original multiplicity by one unit. In Table II and the related discussion, data are presented as evidence that molecular stability is primarily a matter of promotion energy, rather than of valence bonds in the sense of Lewis or London. In connection with Table III, a simple explanation is given of observed multiplet widths $\ensuremath{\Delta}\ensuremath{\nu}$ in $^{2}\ensuremath{\Pi}$ and $^{3}\ensuremath{\Pi}$ states of MH molecules in terms of $\ensuremath{\Delta}\ensuremath{\nu}$ values of corresponding M atoms in states resulting from dissociation of MH. Usually $\frac{\ensuremath{\Delta}{\ensuremath{\nu}}_{\mathrm{MH}}}{\ensuremath{\Delta}{\ensuremath{\nu}}_{\mathrm{M}}}$ is a little under $\frac{2}{3}$; the factor $\frac{2}{3}$ is that expected, according to theory, from the space-quantization of ${l}_{\ensuremath{\tau}}'\mathrm{s}$ to give ${i}_{{l}_{\ensuremath{\tau}}}'\mathrm{s}$.