A Water Strider utilizes the high surface tension of water to stay afloat.
Image from Wikimedia Commons
There are over 1,200 animal species that are able to walk on water, ranging from small insects to large reptiles and birds. These water-walkers have been divided into two groups: slappers and gliders. Through the course of evolution, individual species have developed varying techniques to walk on water, which allows each of their unique anatomical makeups to execute the same talent.
To begin, walking on water is possible because of surface tension. Surface tension is the property of a liquid that allows it to withstand an external force due to cohesive forces between its molecules. Water has strong cohesive properties because water molecules are polar, and therefore attracted to each other. This polarity comes from hydrogen bonding between the oxygen and hydrogen atoms in a water molecule. Because oxygen is a larger atom than hydrogen, it has a stronger electron affinity and therefore draws the hydrogen’s electrons closer to itself. This results in weak hydrogen bonds where the oxygen has a slightly negative charge and the hydrogens have slight positive charges. Water molecules make thousands of hydrogen bonds between each other, giving water molecules strong cohesive forces. Although, because water molecules on the surface of water only have bonds with their neighboring molecules and not the air above them, those neighboring bonds are especially strong and create water’s high surface tension.