WATER!

Dihydrogen Monoxide is responsible for many facts of life that we take for granted.

The beach is typically cooler than the inland regions.

The ocean is cold even when the temperature on the beach is hot.

Small bugs can walk on water.

You can slightly overfill a glass with water, and it won’t overflow.

Dry porous materials draw up water.

Ice floats.

We sweat to cool down.

It feels hotter on a hot, humid day than on a hot, dry day.

The explanations for all these things comes down to the unique molecule that is water. Water is made of two hydrogen atoms and one oxygen atom. When they bond, the oxygen atom is more electronegative (ie electron hungry) than the hydrogen atoms, so the electrons of both Hydrogens tend to spend their time around the Oxygen atom. This results in a slight positive charge on each of the hydrogens that isn’t quite a proper charge, but a positive dipole. The oxygen likewise has two negative dipoles.

So on each water molecule there are four dipoles- and because the elements in question are hydrogen and oxygen, the intermolecular bonds that are formed between the positive dipole of Hydrogen and the negative dipole of Oxygen are H-bonds.

Because of the ease with which water can break and form weak intermolecular bonds, it has a heat capacity of 4.184 joules/ gram Celsius. This means that to heat one gram of water up one degree Celsius, it takes 4.184 joules.

So:

The beach is typically cooler than the inland regions because the ocean and the water vapor from the ocean take won’t heat up as easily.

The ocean is cold even when the temperature on the beach is hot because the sand has a lower heat capacity than water does.

Small bugs walk on water because h-bonds allow for cohesion of water molecules and thus a surface tension that, when treaded upon with the fuzzy feet of small bugs, can hold the bug’s weight.

You can slightly overfill a glass with water, and it won’t overflow because water has such strong cohesive properties that it can sit on top of itself when there is no surface to adhere to. The same property can be observed on a wet penny.

You can also place a toothpick on an overfilled penny and observe the strength of water’s surface tension, which makes it easier to visualize how water bugs walk on water.

Dry porous materials draw up water because some water is attracted to the stronger bonds of the material (adhesion), and the rest of the water tags along because the water molecules are cohesive due to their h-bonds.

Ice floats because water freezes in a hexagonal lattice shape that is less dense than the h-bonded liquid structure.

We sweat to cool down because the heat that allows sweat to evaporate comes from our body.

It feels hotter on a hot, humid day than on a hot, dry day because if there is water vapor pressure in the air, it is harder for your sweat to evaporate (think boiling water in high atmospheric pressures), no matter how much body heat you have. You literally can’t cool down as efficiently. On a hot humid day, drinking water can sub in for the cooling effects of sweating.

-D