As Cold as Ice - A Floating Anomaly

Ever curious why ice floats? Or what would happen if it didn't? Ever think what if water wasn't transparent? Or if it didn't form raindrops? Or if you couldn't boil it in a pot on the stove? Some of the things we take for granted about water are the same things that make it different from almost every other substance on Earth or in the Universe. And if water wasn't different, we might not exist. Water is so unique that it has even been used in science to define temperatures and weights.

It is no coincidence that water freezes at 0^oC (Celsius or Centigrade - 32^o Fahrenheit) and boils at 100^oC (212^oF). That's because these temperatures were set as reference points up until 1954 when more precise measurements defined them more accurately. In 1742, Anders Celsius took his thermometer and put it into freezing water and labeled it 100^oC and did the same with boiling water and called it 0^oC. In 1744, when Anders died, Carolus Linnaeus reversed the scale to be like it is today, with water freezing at 0^oC. Just 51 years later, in 1795, one gram (gm) was defined as equal to one cubic centimeter of water (cc or milliliter - ml).

So going back to our original question, what is it that makes water so different? If we had to boil it down to just one thing, it would be hydrogen bonds. These weak bonds between a hydrogen atom in one water molecule and an oxygen atom in another are what raise the melting point of solid water, help make ice float and create the surface tension to form a raindrop or pull water up a Giant Sequoia.

So how do hydrogen bonds create these unusual properties of water? First lets look at why ice floats. In liquid water the hydrogen bonds form randomly between water molecules, producing a free form molecular mix. The individual water molecules can fit together very closely in this free form state, much like a bowl of random jellybeans. But as the water freezes the hydrogen bonds and the unique bend of the water molecule (see the Chemistry of Water) cause the individual molecules to line up in hexagonal groupings, looking like a beehive, with much more space between them. This results in solid water at 0^oC being less compact than liquid water at 4^oC, the temperature where water is most dense. This beehive arrangement is also why no two snowflakes are ever the same. As water freezes, the hexagon crystals join in an unlimited number of ways to create the snowflakes kaleidoscopic designs.

Since ice, or solid water, has a lower density than the liquid around it, the ice floats to the surface. And thank goodness for that! If ice sank, the water in many rivers and lakes would freeze solid during the winter, supporting no life. Water on lake bottoms at higher elevations would never thaw. The Water Cycle, which helps support life as we know it, that repeating cycle of snow and rain followed by runoff to the ocean returning again to the mountains in clouds would be significantly decreased or non-existent.

So what about boiling water? Well those same Hydrogen bonds hold water molecules together, raising the boiling point. Most similar compounds have long become gases at this temperature. If you like to cook like I do, think of all of the recipes that depend on hot or boiling water. Just the other day I was steaming up some asparagus in the microwave and cooking some spaghetti in boiling water all the while drinking my ice cold diet Pepsi®. Our sweat works in a similar way, cooling us down as it evaporates due to the high energy (heat) needed to change liquid to gas. It removes heat from our skin as the water "boils away". We see that water exists in all three phases; as solid (ice), liquid (water) and gas (steam or water vapor) within the normal temperature range of earth's environment. Few substances on Earth are like this.

Ocean water, with its high heat capacity, is the primary temperature regulator of our environment. It absorbs heat from the sun in the day and releases it at night, keeping temperatures within a livable range all around the World. Without this ability, the temperature at night would drop significantly, possibly to the point where life could not survive.

Hydrogen bonds also make water "sticky." When water sticks to itself it is called cohesion and when it sticks to other molecules it is called adhesion. This stickiness results in two unusual properties of water, surface tension and capillary action. Surface tension is what allows raindrops to form and what keeps the water from spilling over when you fill your glass to the brim. It also allows water bugs to glide on the surface of a lake. Capillary action is the pulling force of the hydrogen bonds that moves water up the roots and stems of plants. As water evaporates out of the leaves, it creates a tension that pulls up the water from within the plant. This force is strong enough to move water to the top of a three hundred foot tall Giant Sequoia.

Pure Water is also transparent to visible light. This property is extremely important to life in lakes, tide pools and the Continental Shelf. Light will penetrate about 50 feet through the water allowing a vast variety of plant and animal life to flourish. Fishing would be tough if this habitable water zone was not possible. We all know that the worst day fishing is better than the best day working!

It is clear that water has many unusual and amazing properties that make it critical for life on this planet. Such a simple molecule plays such a complex role in our lives. We tend to give water little thought, until we're thirsty. Proverbs 25:25 "Like cold water to a weary soul is good news from a distant land." (NIV)