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Martin Harris

Is a bond between beryllium and chlorine ionic or covalent?

Chaw Tin Zar Maung  Follow

I found this sentence on internet:

“Beryllium has a high electronegativity compared with the rest of Group 2, and therefore attracts a bonding pair of electrons towards itself more strongly than magnesium and the rest do. For an ionic bond to form, the beryllium must give up its electrons, but it is too electronegative to do so.”

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David  Follow

Paraphrased from Chemistry of Metallic Elements, by James E. House, in Inorganic Chemistry (Second Edition), 2013:

The chemistry of beryllium (like hat of aluminum) is strongly influenced by the high charge-to-size ratio of their usual ions.

The +2 beryllum ion has a radius of 31 pm (and that of Al3+ is 50 pm). Therefore, the charge-to-size ratios for the two ions are 0.065 and 0.060, respectively.

The electronegativity of Be and Al is 1.6. So the electronegativity difference between each metal and chlorine (with an electronegativity value of 3.2) is 1.6, considered as roughly halfway between ionic and covalent.

(The Si-O bond, in silicate minerals, shows the same difference, and Linus Pauling assessed it as ~ 50% ionic, ~ 50% covalent).

Compounds of beryllium and aluminum are therefore substantially covalent as a result of their high charge-to-size ratio.

Their strong “pull” by the metallic cation on the electronic cloud of chlorine results in the electron pairs being effectively shared between the metal and chlorine.

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