Table of Contents

Structure of water

H2O is a polar covalent molecule. The Bonds between the H atoms and the O atom arise from sharing electrons. These shared electrons form to satisfy the octet rule. However, Oxygen is a “selfish” sharer. This electronegative aspect of Oxygen means that the electrons of the H2O molecule are preferentially located near the Oxygen atom, creating partial charges. We indicate this by placing a δ– near the O and δ+‘s near the H atoms. These partial charges make the H2O polar.

Figure 1. Electrostatic potential of water molecule.
Figure 2: 3D-view of water molecules showing the intermolecular hydrogen bonds.
H-bond simulation. H-bonds can be broken by increasing temperature.

The electron cloud around a water molecule (Figure 1) lingers around the oxygen molecule to render it partially negative. Red illustrates the partial negative end of the molecule while blue indicates the partial positive.

Because of this polarity, H2O molecules arrange in a highly structured way (Figure 2). The partial negative charge of one oxygen atom of one water molecule makes a hydrogen bond (H-bond) with the partial positive charge on the hydrogen of another water molecule. The orientation of water molecules is not random.

Use the following simulation to explore polarity of molecules.

H-bonds are weak interactions that arise from the polar:polar attractions. While independently weak, the summation of all the H-bonds are very strong. These associations give rise to the special properties of water: surface tension, cohesion, adhesion, high specific heat capacity.