Consisting of chains of hydrogen and carbon atoms, soap molecules have two ends with distinct behaviors. On one end of the soap molecule, the atoms -- known as hydrophilic due to an attraction to water -- are grouped. At the other end of the molecule, hydrophobic atoms, which avoid water, are gathered. Hydrophobic atoms are resistant to water, creating the necessary force behind bubble formation.
Soap bubbles are created when water is pressed between layers of soap molecules. The hydrophobic atoms of the soap molecules push at the surface of the water in an effort to escape the water. As these atoms move toward the surface -- the water surface becomes crowded -- and the hydrophobic atoms begin to emerge. Due to the pressure of the atoms vying for an exit from the water, the water molecules begin to split and become farther spaced. Increasing the space between the water molecules allows for the surface tension of the water to decrease and bubbles to form.
Surface tension plays a key role in the formation of bubbles from soap molecules. Regular water has a surface tension three times greater than that of water containing soap molecules. The strength of the surface tension makes it difficult for bubbles to retain form. The reaction of the water to the hydrophobic atoms in the soap molecule lessens the surface tension -- as the water molecules are pushed farther apart.
The longevity of soap bubbles is closely related to susceptibility to evaporation. The more likely a bubble is to evaporate, the sooner it will pop. Bubbles from regular water are more vulnerable to evaporation than those formed by soap molecules; as there is barrier preventing the water from going through the process. In comparison, the hydrophobic atoms contained in soap molecules are resistant to evaporation, and in encapsulating the layer of water, prevent evaporation of the bubble.