Coordination of Electrons in Covalent Bonds

[nothing123]

Do coordinate covalent bonds have to involve the sharing of a PAIR of electrons or can it just be a single electron?

Example: XeF4

Now, since Xe already has a full octet, it would seem correct that the F basically shares electrons to Xe without donating any as well. This would only be true if F only "took" one from Xe since it only needs one e- to fullfill octet. Or are there simply 4 normal covalent bonds formed so that Xe has 12 electrons in outer shell (and violates octet rule).

 

[geoffjb]

Do coordinate covalent bonds have to involve the sharing of a PAIR of electrons or can it just be a single electron?

Example: XeF4

Now, since Xe already has a full octet, it would seem correct that the F basically shares electrons to Xe without donating any as well. This would only be true if F only "took" one from Xe since it only needs one e- to fullfill octet. Or are there simply 4 normal covalent bonds formed so that Xe has 12 electrons in outer shell (and violates octet rule).

XeF_{4} has square planar geometry (each bond to fluorine is in plane, with a lone pair perpendicular to the plane above and below). Each bond is d^{2}sp^{3} hybridized, meaning there are six bonding orbitals in total. Therefore, each fluorine does in fact donate an electron (as does xenon) to each bond (although the electronegativity of fluorine will attract the electrons to a greater extent).

In other words, your last sentence is generally correct (there are four covalent bonds, there are two lone pairs on xenon, and xenon exceeds the octet rule).

 

[sicjeff]

the octet rule is only valid when speaking about the second row. Otherwise, it is junk.