Why Does BeF2 Have Covalent Bonds Despite Being an Ionic Compound?

[mcfaker]

Is BeF2 an Ionic compound??

Hi,

Be is a metal & F is a non-metal. this means its an ionic compound made of cations & anions.
Non-metals form molecular compounds which consist of molecules ( and molecules always contain covalent bonds).

Now if BeF2 is an ionic compound, why does it have a covalent bond? Thats just crazy because the electronegative value of Be is 1,5 and the one of F is 4! This means an ionic bond must be formed!

Can someone please explain, because I am really confused. Thanks in advance!

 

[Borek]

You are a victim of rules of thumb. They work - unless they don't.

There is nothing wrong with the logic you presented - yes, in the perfect world we would expect BeF₂ to be highly ionic. Unfortunately, reality is full of imperfections.

 

[mcfaker]

Thank you for answering!, now I can read on because of your answer. Then how do I know if ts going to be an ionic bond or a covalent? The change of electronegativity must be bigger than what value to become an ionic substance?

Thanks much appreciated!

 

[Borek]

Thank you for answering!, now I can read on because of your answer. Then how do I know if ts going to be an ionic bond or a covalent? The change of electronegativity must be bigger than what value to become an ionic substance?

You are asking for another rule of thumb. I told you there was nothing wrong with your approach, some substances just don't care about our rules. BeF₂ is one of them, other notable example is anhydrous AlCl₃.

Heck, even anhydrous FeCl₃ is covalent enough to sublimate.

To put it another way: you have correctly expected BeF₂ to be ionic. You just have to be prepared to be occasionally wrong.

 

[mcfaker]

So please confirm me if I am right:
The substance BeF2 is a molecular compound with covalent bonds even though there is a difference in electronegativity greater than 2.0 which normally implies that an ionic bond is formed. There is no ionic bond in BeF2 so its not an ionic compound.

So overall this is an exception to the rule that suggests that if the difference in Electronegative values is greater than 2.0 an ionic bond will be formed.

Am I correct?

 

[Borek]

overall this is an exception to the rule that suggests that if the difference in Electronegative values is greater than 2.0 an ionic bond will be formed.

Yes.