# About dative covalent bonding and expanded octet rule

I'm beginning my studies of chemistry at high school (I'm not a native English speaker, though) and I have some basic questions:

1) Consider the compound xenon tetroxide. In this molecule, does the xenon have its valence layer expanded? In another words, the oxygen atoms only have double covalent bonds with the Xenon?

I've tried to look for this answer but I'm still in doubt whether xenon does four dative covalent bonds (with each oxygen) or four double covalent bonds. In the first case, does not occur the expanded octet rule for xenon, right?

2) Another question; is it possible for a dative covalent bond to occur with just one electron? I mean, the atom which has more electrons in its valence layer "donates" just one electron instead of two? If the answer is "yes", can you provide me an example, please?

I'm sorry for the English mistakes. I started to learn this "chemistry vocabulary" just now.

• First of all, welcome to CE.Chemistry! Don't worry too much about your English, it doesn't look too bad to me. There are some capitalization a couple grammar issues that I think I should just fix for you to look at rather than turning this comment into an essay on linguistics ;) Also, have you done any online searches for "dative covalent bond"? You might try that and discuss briefly your thoughts on it within your question. – airhuff Jan 29 '17 at 23:03
• Please do not be discouraged by how many edits I made to your question. It was pretty understandable as it was, but I made more edits than I normally would have just because you stated that you are studying English and I thought that would be helpful. If I inadvertently changed your meaning anywhere please accept my apologies and just change it back. – airhuff Jan 29 '17 at 23:18
• @airhuff I've done some google research, but I havent found a conclusive answer. For instance, in the first question, Ive found two structural formulas for xenon tetroxide, one of them was wih dative covalent bonds, and another with double covalent bonds.. So, I dont know which is the answer... (or maybe this compound can occur with two different bonds...) – gustavoreche Jan 29 '17 at 23:33
• For a description of the bonding in $\ce{XeO4}$ see this earlier answer, – ron Jan 30 '17 at 0:12

To answer your first question: the concept of octet expansion for main group metals is no longer generally considered correct and only upheld by the more traditional organic chemists that don’t deal with inorganic bonding situations on a day-to-day basis — or anybody else who didn’t need to recheck what they were taught decades ago. Nowadays, these seemingly octet-expanding structures such as $\ce{XeO4}$ or $\ce{XeF2}$ are explained by dative bonds and/or four-electron-three-centre bonds; both have the beauty of not requiring d orbitals (whose energy would be comparable to the next shell’s s orbital; remember the aufbau principle!).

To answer your second question: no. A dative bond always requires two electrons that are given to one atom upon supply of the bond dissociation energy. It doesn’t matter how a certain bond is created, it only matters how it dissociates; and if it dissociates and was a bond, it will have to have had an electron pair.

• So, if I understand you correctly ( my studies of chemistry started last week), the xenon, in XeO4, does four dative bonds? I only know dative bonds and ''normal'' covalent bonds... – gustavoreche Jan 31 '17 at 5:11
• @gustavoreche Dative and ‘normal’ covalent bonds are two sides of the same picture. But yes, there’s a single bond between the two and charge separation ($\ce{\overset{+}{Xe}-\overset{-}{O}}$). These bonds can be called dative bonds, if you wish. – Jan Jan 31 '17 at 20:14

(1) For xenon tetroxide all four bonds are double covalent bonds. The electrons from xenon all come from its valence shell.

(2) The definition of a dative covalent bond is that both electrons come from the same atom. So something like $\ce{H+ + NH3 -> NH4+}$. Both electrons come from the N molecule.

• So, the xenon, in XeO4, will have 16 electrons in its valence shell? – gustavoreche Jan 30 '17 at 0:23
• These aren't really double... and no such thing as octet expansion is needed to describe it. – Mithoron Jan 30 '17 at 0:52
• Now I'm confused... @Mithoron, what do you mean? – gustavoreche Jan 30 '17 at 0:57