Question

Can anyone explain non-polar and polar compounds and why do polar compounds dissociate in water and polar compond?

Answer 1

basically,polar compounds have a net dipole moment whereas non polar do not.Polar compounds r attracted by polar solvents.Like H of water attracts negative part of polar substance.,so they dissolve.

Answer 2

Polar compound :
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The greater the electronegativity difference, the more ionic the bond is. Bonds that are partly ionic are called polar covalent bonds.

Non-Polar compound :

These are achieved when the electro negatives of the two atom are same .
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dissociation of the solvent in the water depend upon its hydration enthalpy and bond enthalpy
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The hydration enthalpy of the polar solvent is more than that of its bond enthalpy so it dissociate in water  . 
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But in the case of non- polar the bond enthalpy is more that hydration enthalpy hence it not dissociate . 
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