# BeF2 : covalent or ionic?

My textbook says despite large electronegativity difference it's covalent since beryllium ion will have too much charge density and it'll attract fluorine election cloud and therfore forms polar covalent bound.

But I looked it up in Wikipedia and found out that it has a crystal lattice, is Soluble in water and has a quiet high melting point.

What else one needs to call a compound ionic? Am I or the textbook right?

Thanks for your help!

• I am not putting this as an answer but bond between 2 different atoms is usually not completely covalent nor completely ionic: it is a mixture of them. We prefer to talk about the "covalent" or the "ionic" character of a bond. – SteffX Aug 9 '16 at 19:13
• And BeF2 probably has more ionic then covalent character, not that it matters much. – Mithoron Aug 9 '16 at 19:16
• Nearly anything has a crystal lattice. Many covalent compounds are soluble in water (and quite a few ionic ones are insoluble). As for the melting point, well, it's moderately high, so consider $\ce{BeF2}$ moderately ionic and stop pursuing this false dichotomy. Also, I suggest to close this question as a duplicate of AlCl3: ionic and covalent?, because though the title compounds are different, just about every argument applies equally well to both. – Ivan Neretin Aug 9 '16 at 19:40
• – Mithoron Aug 9 '16 at 20:31
• @IvanNeretin "All bonds to fluorine, with the exception N-F, O-F, and F-F, have considerable ionic character, so the vast majority of AFn molecules are more appropriately described in terms of an ionic model rather than a covalent model." pubs.acs.org/doi/abs/10.1021/ic961315b BeF2 is much more extremely ionic than AlCl3 , with Be having a +1.8 charge. The AlCl3 answer does not apply well to BeF2. – DavePhD Aug 10 '16 at 13:02

## 2 Answers

There is a very relevant article by Gillespie Covalent and Ionic Molecules: Why Are BeF2 and AlF3 High Melting Point Solids whereas BF3 and SiF4 Are Gases? J. Chem. Educ., 1998, 75 (7), p 923.

According to the article, the charge on Be is +1.81 and the charges on the Fs are -0.91. (citing to his earlier article Reinterpretation of the Lengths of Bonds to Fluorine in Terms of an Almost Ionic Model Inorg. Chem., 1997, 36 (14), pp 3022–3030)

So while nothing is completely covalent or ionic, BeF2 is extremely toward ionic.

According to my chemistry book (Pearson Baccalaureate IB) beryllium forms covalent bonds due to it being one of the expectations to the intramolecular bonding.

Furthermore, according to the book the molecule should be non-polar because all the lone pairs are bonded and thus not exerting a repulsion and altering bond angles.

• I think you are confusing polar bonds with dipole moment. Also, I doubt that any element will always form a covalent bond. Maybe you meant that beryllium forms covalent bonds with itself? – CoffeeIsLife Jan 15 '17 at 18:15
• I didn't say always , furthermore no, I'm not confusing those two together – Melodishhh Jan 17 '17 at 20:36