Hydrogen atoms can form a single bond to each other, oxygen atoms can form a double bond to each other, and nitrogen atoms can form a triple bond to each other. Is there any element that can form a quadruple bond? — KC, Mendenhall, MS

The bonds that you are referring to are call “covalent bonds,” in which two atoms share a pair of electrons in order to lower their total energy. When two electrons are shared in this manner, the electrons are able to spread out over two atoms rather than one. This broadening of their territories lowers their kinetic energies because of quantum mechanical effects. The electrons also spend large portions of their times between the atoms, where they lower the electrostatic potential energies of the two atoms. Lowering the total energy of the two atoms binds them together.

The number of covalent bonds that form between two atoms depends on the number of electrons in those atoms. Hydrogen atoms have only one electron each and can form only one covalent bond. Oxygen atoms have two electrons each that they can share and form two covalent bonds. Nitrogen atoms have three electrons to share and form three covalent bonds. And carbon atoms have four electrons to share, so you might expect them to form four covalent bonds. But there’s a hitch…

In the first covalent bond that forms between two atoms, the pair of electrons positions itself directly in between the atoms. This arrangement is most effective for lowering the energy of the system and binding the two atoms together. Chemists call this arrangement a “sigma bond.” In the second covalent bond, the two electrons position themselves on both sides of the sigma bond. If you picture the atoms as two people facing one another and holding hands, the electrons are located along the arms of the two people. This arrangement is reasonably effective for lowering the energy of the system and is called a “pi bond.” The third covalent bond is also a pi bond, but it forms 90° from the first pi bond, as though the two people are now touching their heads and their feet together along with their hands. With a sigma bond and the two pi bonds between the atoms, there is no room for additional electrons. The fourth covalent bond that two carbon atoms would like to form with one another simply can’t form. While two carbon atoms will bind together with a triple bond, each atom will have one remaining electron that is still seeking a partner. The carbon dimer molecule is a highly reactive double radical that will bind to just about anything it encounters.

Does the pull of the moon have any effect on a person’s behavior? — PSC, Summerville, WV

No, but for an interesting reason. While the moon’s gravity acts on people, it also acts on everything around them and everything falls toward the moon at the same rate. Because of this uniform falling, we don’t feel the moon’s gravity at all. This effect is identical to the one that astronauts feel as they orbit the earth—the earth’s gravity pulls on them and on their spaceship, but they are falling freely under the influence of that gravity and they don’t feel it—they feel weightless. Since we are falling freely under the influence of the moon’s gravity, we don’t feel it either—we feel moon-weightless.

Since we are being pulled toward the moon by the moon’s gravity, you might wonder why we don’t crash into the moon. That’s because we’re traveling sideways so fast that we perpetually miss the moon and circle it once every 27.3 days. Similarly, the moon perpetually misses the earth and circles it, too.

The only significant effect of the moon’s gravity is to create the tide. The earth’s oceans are so large that they’re sensitive to variations in the moon’s gravity. The moon’s gravity decreases with distance from the moon, so that the oceans on the near side of the earth are pulled harder than the oceans on the far side of the earth. The result is two bulges in the oceans—one on the near side of the earth and one on the far side of the earth. These bulges create the familiar high and low tides that we observe at the seashore.

Is the fact that the small magnetic fields generated by appliances change due to the alternating electric current the reason that EMFs may cause health problems? — MC, Independence, KS

I believe that the alternating nature of the electromagnetic fields around appliances is at least part of the reason they’re suspected of causing health problems. Since these fields are created by an electric current that alternates in direction, they alternate in direction, too. However, I have not seen any credible evidence for there being a relationship between these appliance-related fields and health problems, nor have I heard any sensible physical theory for such a possibility. On the contrary, I have read a number of compelling arguments for why the tiny electromagnetic fields around appliances should have no biological effects at all. I think that the worries about EMFs are unfounded.