Strange things about BeF2

BeF2 look like an ionic compound but it is said to be a covalent compound! I search for many websites but both answers can be found! Which one is correct?

The difference in electronegativity between Be and F is very high, so it should be ionic,right?

However, BeF2 is said to be covalent in nature (from both wiki and my textbook), but the structure violates the ocetet rule again even for period 2 elements!


Is LiF ionic or not? With your explanation, LiF should be covalent since it also contain 1 electron shell ,how about AlF3?

更新 2:

Oops, I mean BF3

2 個解答

  • 9 年前

    BeF2 is mainly covalent in nature. The central Be atom is linked with the two F atoms by very polar Be-F bonds.

    Consider the case if BeF2 is ionic. Be^2+ carries 2 positive charges, and is very small in size as it has onlyone filled electronic shell. Therefore,the charge density of Be^2+ is very high, leading to very high polarizing power(i.e., the power of cation drawing back electron clouds from anion). Be^2+ draws back electron clouds from F^- toa great extent, and thus the bond between Be and F is a very polar covalent bond.

    2012-03-19 02:57:44 補充:

    LiF is ionic.

    Although Li^+ ion has only one electronic shell, it carries one positive charge only. Besides, the size of Li^+ is greater than that of Be^2+. Therefore, the charge density and polarizing power of Li^+ is much lower than that of Be^2+, and thus LiF is ionic while BeF2 is covalent.

    2012-03-19 03:05:04 補充:

    AlF3 is covalent (molecular) in nature.

    The charge density and polarizing power of Al^3+are greater, because Al^3+ carries 3 postive charges and its size is rather small.

    2012-03-20 23:44:18 補充:

    BF3 is covalent (molecular). Both B and F are classified as non-metals.

    資料來源: micatkie, micatkie, micatkie, micatkie
  • 匿名
    9 年前

    For easy understanding

    just take a look to the EN difference.

    2012-03-20 19:03:21 補充:

    There are sth in between ionic and covalent

    It is not true that we only divide compounds by ionic and covalent

    still sth are mainly ionic ionic/covalent ....