After reading this article you will learn about the structure and related properties of water molecules.
One oxygen atom combines with two hydrogen atoms by sharing a pair of electrons with each of them. But the electrons are not shared equally. They are nearer to the oxygen than to the hydrogenâ€™s.
Consequently, a weak negative charge develops on the oxygen side of the water molecules and a weak positive charge develops on the opposite hydrogen side of it. Hence water molecules are dipolar which means that they possess positive and negative poles. Two hydrogenâ€™s are connected with one oxygen at an angle of 105Â° as shown in the Fig. 5.1.
The negative poles of the first water molecule attract the positive pole of the second water molecule, the negative pole of which attracts the positive pole of the third water molecule and so on. In this way a long chain of water molecules are formed in nature. This phenomenon by which hydrogen atoms act as connecting links between water molecules is called Hydrogen Bonding.
Surface Tension is the force in dynes per centimetre acting upon an imaginary line of one centimetre length on the surface of water, which tends to compress the surface area. Water molecules (tiny circles in Fig. 5.2) within water are attracted in all directions by the surrounding water molecules.
In Fig. 5.2 water molecules (tiny circles) are attracted from all sides by the surface of water are pulled in all direction except vertically upwards. Hence they are pulled in the vertically downward direction as shown in Fig. 5.2.
The surface of water is under some tension, which is known as surface tension. In a similar way the solid surface also attracts water molecules, which is known as adhesion. The attraction between water molecules is known as cohesion.
Fig. 5.2. Water molecules (tiny circles) are attracted from all sides by the neighboring water molecules inside water. But water molecules at the surface are attracted from three sides so the surface is slightly curved in the downward direction.
Place one end of a fine glass tube called a capillary tube in water. Water molecules inside the tube are attracted by the inner surface of the tube. These water molecules attract other water molecules. Hence water rises in the capillary tube.
Pressure on the water surface is lower inside the tube than outside the tube. The pressure on the surface of the water outside the tube is the atmospheric pressure. Consequently water is slowly pushed up inside the capillary tube till the weight of the column of water inside the tube is equal to the difference in pressure inside and outside the tube.