Anomalous Behaviour of Beryllium Chemistry

Chemical properties of Be are different from the rest of group 2 elements.

 

Group 2 contains soft, silver metals that are less metallic in character than the Group 1 elements. Anomalous Behaviour of Beryllium Chemistry: The anomalous properties of beryllium is mainly due to its small size, high electronegativity, high ionization energy and high polarizing power compared to the other elements in the block.

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Element of group 2: Be, Mg, Ca, Sr, Ba.

1. Beryllium, Be has a small size, but the others large. When down group 2, atomic radius is increases.

2. Beryllium, Be has high charge density.

3. Beryllium, Be has strong polarising effect of small Be2+.

4. Beryllium, Be can distort the electron cloud of anions.

5. When Beryllium, Be combine with larger anion, more covalent character of compound formed.

6. Beryllium, Be compounds tends to form covalent compouds rather than ionic compounds. The compound form has covalent molecule nature but not ionic.

BeBr2 = covalent
MgO = ionic
CaF2 = ionic
SrSO4 = ionic

BeCl2 = covalent
MgCl2 = ionic
CaCl2 = ionic
SrCl2 = ionic
BaCl2 = ionic

7. Amphoteric hydroxides react with both alkalines and acids.

Amphoteric, can dissolve (react) in NaOH & HCl.

BeO is an amphoteric oxide of group 2 while other elements of group 2 forms basic oxide.

BeO = covalent character & amphoteric.

BeO = amphoteric (both)
MgO = basic (alkaline)
CaO = basic (alkaline)
SrO = basic (alkaline)
BaO = basic (alkaline)

BeO, beryllium oxide, has lower melting point than MgO because #6.

The melting point and boiling points of group 2 (overall) are higher when compared to the other elements of the group.

Be(OH)2 = amphoteric (both)
Mg(OH)2 = basic (alkaline)
Ca(OH)2 = basic (alkaline)
Sr(OH)2 = basic (alkaline)
Ba(OH)2 = basic (alkaline)

Read related article here Option 1, Option 2.

8. BeCl2 = dissolve in water, hydrolysis in water to produce acidic solution, H3O+ ions, acidic pH<7.

Which one has lowest pH (acidic) when dissolve in water? NaCl, KCl, BeCl2, MgCl2.

Lowest pH is BeCl2 (acidic)
MgCl2 (weak acid)
NaCl and KCl (neutral solution).

9. BeCl2 = can form dimer because #2. Can form dimer, Be2Cl4, because Be atom has an incomplete octet, the lone pair from the Cl atom utilised to form dative bond with Be.

10. Beryllium, Be act as a strong reducing agent, it can reduce Ag+ –> Ag.

11. Beryllium, Be can form complex ions because #2. A complex ion is a cation bonded to small molecules called ligands by dative bonds.

A dative bond is a covalent bond between two atoms where one of the atoms provides both electrons that form the bond.

[Be(H2O)4]2+ hydrated ion, when hydrolysed will form molecule with pH < 7 which is acidic.

12. Beryllium, Be soluble in benzene (inorganic solvent), other element in group 2 insoluble/ decreases when down group 2. Example, BeCl2 dissolve in benzene.

13. Electronegativity chart: Electronegativity is basically a chemical property that describes how an atom can attract with an electron in very well way. Values that electronegativity run from 0 to 4. As we all know electronegativity is used to assume the bonding between atoms and also see that they are iconic or covalent, we can also predict that the result of molecules will be polar or non-polar. And now I provide you a table by which you can easily know about electronegativity charges about all elements and you just need to go through it.

electronegativity chart

14. Be, beryllium’s valence electron is very near to nucleus. Be, beryllium more electronegative, less reactive, its electron hard to be released during reactions.

Reaction of elements group 2 with water:

Be = no reaction ❌
Mg = hot steam ✅
Ca = normal water ✅
Sr = cold water ✅
Ba = cold water ✅

15. Down to group 2, from Beryllium to Barium, reactivity increases.

Reactivity increases from Be to Ba, when down group 2. Because atomic radius and shielding effect increases.

Valence electrons further from nucleus, the large shielding effect, weaker the nuclear pull towards the electrons, easier for metal to lose electrons.

16. Melting point of:
BeCl2 = 399’C
BaCl2 = 962’C
Why?

BeCl2, simple molecular structure molecules held by weak van der Waals forces.

BaCl2, giant ionic structure, ions held by strong ionic bonds.

17. It is a characteristic of abnormal (ganjil) behaviour of beryllium and it shows diagonal relationship with aluminium.

Chemical properties of Be is similar to Al3+. Which can form complex ions (#11). Similar to Al3+ is an amphoteric compound.

Be2+ + 2NaOH –> Be(OH)2 (white ppt) + 2Na

Be2+ react with 2NaOH, sodium hydroxide, will produce white precipitate,

When further added –> soluble ion formed [Be(OH)4]2-. Complex ion further added because #2.

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