The first molecule featured in the Daily Molecule series is the molecule most vital to all life – water! Water, with the chemical formula H2O, contains two hydrogen atoms and an oxygen atom covalently bonded together.
Water can be found all over the planet – roughly 71% of Earth’s surface is covered in water. But less than 1% of all water is useable to human beings. 97% of the water on Earth is contained by the world’s oceans. Of the remaining 3% of freshwater on the planet, more than 2% is frozen in the world’s glaciers and icecaps. That leaves less than 1% of all the water on our planet that is useable by humans! This freshwater can be found in the ground and in bodies of water such as rivers, swamps, and lakes. It’s fascinating to think that of the incomprehensible amount of water on this planet, such a small fraction can be used by humans.
The water molecule has some very interesting properties for something that seems so simple. Most of these properties stem from the fact that water is a polar molecule. This means that the electrical charge of a water molecule is not evenly spread out due to an uneven sharing of electrons in bonding, giving the molecule “positively” and “negatively” charged ends. This polarity is caused by differences in electronegativity between the oxygen and hydrogen atoms. Oxygen has a high electronegativity, while hydrogen’s electronegativity is relatively low.
When compared to other polar molecules, water is a very strong polar molecule. Water is often called the universal solvent because of the almost endless list of molecules it can dissolve. Since the oxygen atom in a water molecule has two lone pairs of electrons and is highly electronegative it easily causes most other polar molecules to dissociate and form new bonds with the water molecule.
Another unique property of water is a result of its molecular geometry and polarity. Water molecules form hydrogen bonds with one another, leading to the properties of adhesion and cohesion. The term hydrogen bond is a bit misleading, as it implies that bonds are actually being formed. Really hydrogen bonding results in no actual bonds being formed at all. Rather, a hydrogen atom of one water molecule forms a strong attraction with the one of the lone pairs of electrons on the oxygen atom of another molecule. Since the atoms in a water molecule are covalently bonded with the oxygen molecule getting the largest share of the electrons (in order to complete its desired octet electron formation), the hydrogen atoms are left seeking out other electrons to fulfill their need for negativity. The lone pair electrons on the oxygen atom of a water molecule are just what those hydrogen atoms need. What’s unique about this interaction and attraction between the oxygen and hydrogen of separate water molecules is that each water molecule can form hydrogen bonds with four other water molecules. This causes water molecules to stick together very well, causing the phenomenon of surface tension.
Water occurs in three states of matter – solid (ice), liquid (water), and gas (steam). Each of these states has its own name, which is another unique fact about water. These different names for the different states of water exist because language was formed before science had been developed enough to prove that each of these three states were indeed made up of the same molecules. Ice, when it occurs naturally in the environment, is also considered a mineral.
Water is a simple, yet fascinating molecule. Many of the wonders of water are not covered here for the sake of length, so there is plenty more to research and read about water! Always be sure not to waste water and to do your part in protecting the natural cycling of water in order to sustain life on our planet indefinitely.
Chemistry of Hurricanes
As a Florida resident within walking distance from the Atlantic Ocean, hurricanes are a fact of life. As we trudge through hurricane season, I figured I’d explore the chemical basis for these destructive natural phenomena. What do hurricanes have to do with chemistry? Quite a bit, it turns out.
You know of course, that water is somewhat special. Those hydrogen bonds keep water’s boiling point abnormally high for its size. It also has a high vaporization energy. This has important implications for people who live along coastal regions of the southeastern U.S., the Gulf of Mexico, and in the Caribbean at this time of year. Hurricanes form when low pressure systems develop over warm (greater than 80 ºF) water in the tropics. Warm moist air near the ocean surface rises to higher altitudes. As the water vapor rises, it cools and condenses. The thermochemical equation for this process is:
H2O (g) → H2O (l); Δ H = -44 kJ/mol
This exothermic reaction releases heat, warming the atmosphere, causing air to rise. More warm, moist air rises, and more water vapor condenses.
As long as the system is over water, it can continue the process. When the storms make landfall, they quickly weaken because there is no longer enough water to provide the energy needed to sustain the storm.
It’s often said that no two snowflakes are the same shape. Beginning as snow crystals which develop when microscopic supercooled cloud droplets freeze, complex shapes emerge as the flake moves through differing temperature and humidity regimes, such that individual snowflakes are nearly unique in structure. Although statistically possible, it is very unlikely for any two snowflakes to appear exactly alike due to the many changes in temperature and humidity the crystal experiences during its fall to earth.
These peculiar natural phenomena are formed on new layers of sea ice from saturated water vapors that come up from under the ice through cracks. In contact with the cold air, the vapors start to freeze and the salt on the surface of the ice begins to crystallize, serving as a base for the sublimated water to build off of. The ‘petals’ of ice flowers are very delicate and will come off when touched. They usually form in sunlight and typically are visible in the early mornings or in shaded areas.