WATER: in 3-D

    Water properties can be grasped once it is understood that the oxygen atom has a three-dimensional quality to it. In the above diagram, the oxygen atom is red and the hydrogens are yellow. Once it has shared electrons with hydrogen, the four pairs of electrons repel each other such that they come to lie as far apart as they can get in three-dimensional space. One might at first wonder why even two electrons would pair up, but remember that electrons have spin, and spin begets an electromagnetic field. It will attract an electron with the opposite spin so that their opposite fields cancel each other. Afterall, water is not known to be magnetic!

    Thus when two hydrogen atoms approach an oxygen atom they must of necessity find themselves more-or-less on one side of the oxygen atom. This leaves two pairs of the oxygen's electrons cross-wise on the opposite side of the oxygen. Thus that side is negatively charged, while the hydrogen side (two protons actually) is positively charged. The asymmetric separation of the two sides' charges is called water's dipole moment. Note that on the picture, there is a significant measureable distance ("moment") between the positive and negative sides of the molecule. (Were water to be a linear molecule as many beginners are wont to draw it, there would be no "moment" - because the drawing would be symmetrical.)

    When you have a conglomeration of water molecules, each one will position itself such that its positive side will snuggle near the negative side of another water molecule. This is not unlike what would happen were you to have throw a number of weak bar-magnets together - they'd weakly stick together. Each sticky bunch would act as if it were a sort of larger molecule, and thus the partners in that bunch would find it more difficult to evaporate than single ones alone. Thus water's boiling point is much, much higher than its simple molecular weight would suggest. It might here be mentioned that water's sulfur analog, H₂S, has a much smaller dipole moment because the distribution of outer-electron pairs on the larger surface of a sulfur atom are much more widely spread out. Thus, while of much higher molecular weight than water, H₂S is a gas at normal temperature and pressure.*

    Furthermore, these conglomerations tend to form a thin skin across water's surface with air. This skin is more difficult to penetrate than the surfaces of liquids which don't have dipole moments. Thus water has a surprisingly strong surface tension upon which steel needles can be floated, and which forms a meniscus in cylinders, or which can bulge up over the lip of containers which are over-filled.

    Water is a wonderful substance because of this simple property of possessing a dipole moment. Life could not exist without it!

    Do not confuse dipole moments with zwitterions. The strengths of the charges on water molecules are smaller than full "plus" or full "minus". Often they are written as "δ+" or "δ-", meaning partial charges. Thus water's conglomerations are by what are called H-bonds, which are weaker than ionic bonds (as between zwitterions with their full charges). This is why, in the magnet analogy, above, weak magnets were mentioned and not strong ones.

* WARNING! Don't play around with H₂S. While you might think it fun to make stink bombs of it, remember it is more toxic than phosgene, a war gas. One good sniff of a strong batch will have you dead before you hit the floor.