Structure of water

Water consists of two hydrogen and one oxygen atoms. Out of eight electrons, only four are involved in electron pair formation with two hydrogen atoms. A strong attractive force is exerted by the oxygen on the remaining for electrons, making hydrogen atoms electropositive. The geometrical shape of water molecule is that of a tetrahedron in which the oxygen atoms is in the centre and two hydrogen’s occupy two of the corners.

The water molecule in a liquid state attracts four other molecules, which are oriented in a tetrahedral fashion. However, frozen water or ice forms a crystalline lattice in which the arrangement of molecules is more ordered but loose.

X-ray analysis has shown that the bond angle in water molecule H – O – H is 104.5° and the intra-atomic distance is 0.965Å  (H – O). There is some electrical asymmetry in the molecule; each hydrogen atom has a partial positive charge and the oxygen atom a partial positive charge and the oxygen atom a partial negative charge. The dipole nature gives rise to forces of attraction between the negatively charged hydrogen atom of the neighboring water molecule. The electrostatics interaction gives rise to hydrogen bonding which are wealk with about 4.5 kcal mole -1.

   
Tetrahedral shape of water molecule showing bond angles and bond distance

 
 
Tetrahedral structure of water molecule in ice


Arrangement of water molecules in ice showing crystalline lattice