2008 Woodie Awards
Water Water Everywhere
Professor Janet Anderson: Chemistry Department
Issue date: 9/20/07 Section: Sci/Tech
- Page 1 of 2 next >
The importance of water in our world cannot be understated-one of the first things we look for when exploring other planets is the presence of water, because we know that living things on Earth require it. Your body is approximately 60% water by weight, and you can survive for weeks without food but only a few days without water. Water is the major component of blood and most (but not all) of the nutrients in food are soluble in water. Athletes know that adequate hydration is a key component of top athletic performance, and even the weekend bike rider or runner discovers soon enough that one can develop a headache just from sweating and not replacing the lost water.
The biological and geological aspects of water are huge topics in themselves, but we will focus here on the physical and chemical properties of water that make it such a unique molecule. The chemical formula of water is H2O, but the structure of water is bent with the oxygen atom (O) placed between two hydrogen atoms (H), forming a bond angle of around 104?. Just as important as the bonded hydrogen atoms are two unbonded pairs of electrons "sticking out of" the oxygen atom at angles as far apart as possible from the bonded hydrogen atoms. These unbonded electrons (called "lone pairs") are strongly attracted to hydrogen atoms in other water molecules, creating interactions called hydrogen bonds.
The properties of liquid water are determined by the network of hydrogen bonds that form and are broken as the molecules move around each other. When you pour a glass of water on the floor, hydrogen bonds are broken and new ones are created as the liquid changes shape. Drops of water have curved surfaces because the surface water molecules can make hydrogen bonds to those molecules inside the drop, but not to the air, and a curved surface is the most stable way to do that. Liquid water rises in a narrow glass tube (capillary action) for similar reasons; only the shape of the curved interface between liquid and air is concave rather than convex because of water's attraction to the silicon-oxygen bonds in glass.
The biological and geological aspects of water are huge topics in themselves, but we will focus here on the physical and chemical properties of water that make it such a unique molecule. The chemical formula of water is H2O, but the structure of water is bent with the oxygen atom (O) placed between two hydrogen atoms (H), forming a bond angle of around 104?. Just as important as the bonded hydrogen atoms are two unbonded pairs of electrons "sticking out of" the oxygen atom at angles as far apart as possible from the bonded hydrogen atoms. These unbonded electrons (called "lone pairs") are strongly attracted to hydrogen atoms in other water molecules, creating interactions called hydrogen bonds.
The properties of liquid water are determined by the network of hydrogen bonds that form and are broken as the molecules move around each other. When you pour a glass of water on the floor, hydrogen bonds are broken and new ones are created as the liquid changes shape. Drops of water have curved surfaces because the surface water molecules can make hydrogen bonds to those molecules inside the drop, but not to the air, and a curved surface is the most stable way to do that. Liquid water rises in a narrow glass tube (capillary action) for similar reasons; only the shape of the curved interface between liquid and air is concave rather than convex because of water's attraction to the silicon-oxygen bonds in glass.
Be the first to comment on this story