Halide anion transfer from NaCl

The ionic model describes a number of metal halides, oxides, and sulfides, but it does not describe most other chemical substances adequately. Whereas substances such as CaO, NaCl, and M 2 behave like simple cations and anions held together by electrical attraction, substances such as CO, CI2, and HE do not. In a crystal of Mgp2, electrons have been transferred from magnesium atoms to fluorine atoms, but the stability of HE molecules arises from the sharing of electrons between hydrogen atoms and fluorine atoms. We describe electron sharing, which is central to molecular stability, in Chapters 9 and 10. 

The extent to whieh eharge is transferred baek from the anion towards the eation in the alkali metal halides themselves is diffieult to determine preeisely. Caleulations indieate that it is probably only a few pereent for some salts sueh as NaCl, whereas for others (e.g. Lil) it may amount to more than 0.33 e" per atom. Direet experimental evidenee on these matters is available for some other elements from teehniques sueh as Moss-bauer speetroseopy, eleetron spin resonanee speetroseopy, and neutron seattering form faetors. ... 

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