[penguin]

Why water can form ions?
Why water can form ions and something like that?
Isn't water built up using covalent bonding? But I doubt that why H+ can form and OH- can form.

Also, why water can make molecule dissolve? I know the situation of ionic compound but I do not know about covalent bonding compound. 

 

[xiankai]

Why water can form ions?

because it can dissociate into two oppositely charged ions, H⁺ and OH^-. this is very difficult though, and hence water only dissociates a tiny bit (the K_w of water, the ratio of its ions to its covalent form, is 1.8 x 10^-16 : 1)

Isn't water built up using covalent bonding? But I doubt that why H+ can form and OH- can form.

water is made up of ionic bonding, between the H and O atoms.  H⁺ and OH^- form because they are the stable products of the dissociation of water (here stability is relative, what i mean is that it is more stable compared to other products like H₂ + O).

also, H⁺ itself is not stable. hence in reality it binds to a water molecule, giving us H₃O⁺ instead.

water can make the molecule dissolve because it attracts the oppositely charged ends of the molecule. the H in water is partially positive, and attracts the negative part of the molecule. likewise, the O in water is partially negative and attracts the positive part of the molecule. thus the molecule is 'ripped' apart into positive and negative ions.

Also, why water can make molecule dissolve? I know the situation of ionic compound but I do not know about covalent bonding compound.

for covalently-bonded compounds, water fails to dissolve them in general, because of the lack of opposite charges. here however, abit of dissolution still takes place, mainly due to the van der waals interaction between water and the compound. since all atoms/molecules/compounds have an electron cloud, sometimes the electron cloud shifts (it is not a fixed orbit), and then there is a tiny imbalance in the charges, thus giving it opposite charges. thereafter it is the same thing with ionic compounds, although on a very small scale