Water: One of the key ingredients for life and yet possibly one of the most underrated chemicals considered in Science classes. Water behaves very differently to many other liquids and due to its chemical composition and structure has unique properties. Most importantly, water is a safe substance that everyone has access to so can easily be studied in the home or classroom.
Water (H2O) is composed of two hydrogen atoms per oxygen atom. The hydrogen atoms tend to bond to one side of the oxygen atom. They have a positive charge so make this side of the molecule slightly positively charged. The oxygen atom is negatively charged, and thus the other side of the molecule will have be partially negatively charged. This gives the water molecule POLARITY, like a magnet with opposite charges on each side. This means that the positive end of one water molecule is attracted to the negative oxygen atom in a neighbouring water molecule. This type of attraction is called hydrogen bonding. It makes water highly cohesive, in fact it is the most cohesive of all non-metallic liquids. This cohesion is what causes water tension and explains why water will clump together, forming droplets.
Water is a polar molecule (Koning, Ross E. 1994. Water and Water Movement. Plant Physiology Information Website. http://plantphys.info/plant_physiology/watermove.shtml (4-1-2020))
Cutting through the tension
Similar to water, detergent and soap have differences on the sides of their molecules. One end is hydrophilic (attracted to water), the other end is hydrophobic (repelled by water), and attracted to fats. This allows them to stick to the grease from a dirty dish and use the other end of the molecule to stick to a water molecule to wash the fat away. When detergent is dropped into water the hydrophobic ends of the molecule will attempt to move away from water molecules. The hydrophobic ends of the detergent molecules push up to the surface. The hydrogen bonds in the water are then weakened and this leads to the surface tension breaking.
Investigating Surface Tension
For a few ideas on short, simple experiments that can be carried out at home watch our YouTube video.
For more information and activities, like those featured in our video, click here.