[shehri]

Hi friends,

              I've read in my book that MgO & BeO're insoluble in water.But there's no reason.Can somebody explain it to  me?Thanks.

[vijaychatare]

Hi,
In case of BeO and MgO are not soluble in H2O. Becoz covalent bonding is present in their arrangement. so all covalent bonded compounds are not soluble in H2O.i think so this may be the reason...

[Borek]

all covalent bonded compounds are not soluble in H2O.

Sugars are covalent & soluble.

[shelanachium]

High lattice energy - that is, the binding energy resulting from the electrostatic attraction of the oppositely-charged ions in the structure. The Be2+ and Mg2+ ions are small, so the metal-oxygen distance is small in the oxides, and the lattice energy high. As the metal ion gets larger the metal-oxygen distance increases and the lattice energy falls. When oxides dissolve in water the species formed is not O2- but OH-. Hydroxides, as the OH- ion is but singly charged, have much lower lattice energies than oxides, so the oxides of metals with small and/or highly-charged ions and therefore with high lattice energies do not easily convert to the hydroxides with much lower ones.

The larger elements Ca, Sr and Ba have oxides with lower lattice energies that spontaneously react with water to give the hydroxides - as in 'slaking' of quicklime:

CaO + H2O ---> Ca(OH)2

and these become increasingly water-soluble with increasing atomic number.

Water-soluble covalent compounds like sugarsusually contain groups that hydrogen-bond to water. Sugars have numerous hydrogen-bonding  O-H groups.

[agrobert]

Don't forget that organic ionic salts and sulfonic acids are often water soluble.