Breaking Bonds

In the last post I briefly, and possibly badly explained plasma science and the moon melting. Let me back up a few steps to better explain my field of research. In this post, I’ll start with the basics: atoms and bonds. (It does get more basic if you look into the atom, but that’s a realm of physics I don’t work in and is really far removed for our everyday intuition).

Everything we see and don’t see is made up of atoms. This is something we all learn sometime in middle school science class. The periodic table shows all of the atom species we have discovered so far. Some are naturally occurring like oxygen, iron, and gold. Others we have created in the lab. These are the usually the ones at the bottom of the table with funny names like Einstienium, Bohrium, and Ununtrium. These species are not stable enough to exist naturally, and quickly break down into more stable species. By themselves, most of the atomic species aren’t very useful to us. For example, water, which all life on Earth depends on, is a combination of two hydrogen atoms and one oxygen atom, H2O. The hydrogen and oxygen atoms are held together via their electrostatic attractions between the positively charged nuclei, and the negative electrons orbiting the nuclei. This is how all complex molecules are held together, with the attraction between positive and negative charges.

Now, if you want to break a water molecule back into hydrogen and oxygen, you have to put some energy in. Water is a stable state, meaning the attraction and repulsion forces in the molecule are balanced. So the two bonds have no good reason to break. However if we hit the water molecule with a large burst of energy in the form of heat, light, or electricity, the energy will cause the molecule to start shaking and vibrating. The bonds will start to get stretched and weakened. If enough energy is put into the water molecule, the individual hydrogen and oxygen atoms will be energetic enough that their bonds become weak and eventually break. Think of a paperclip. It’s pretty strong, but if you put energy into bending it back and forth, eventually the metal breaks. Or another analogy is to think of a bunch of little kids holding hands in a circle. If you give them a lot of candy (energy), they’re going to start moving around a lot more and eventually they’ll break their hand holds.

So this is how you get hydrogen and oxygen gas from liquid water, typically using electricity in a process called electrolysis. Thus bonds are stable, balanced links between the nuclei and electrons in an atom, and you can break bonds by putting energy into the atoms that cause them to vibrate and move away from each other such that the bond weakens and then breaks. It takes about 464 kJ/mol of energy to break one of the H-O bonds in water. If you break water, you now have hydrogen and oxygen atoms in a gas state. Now if you continue to put more energy into the gas, you start energizing the electrons in the atoms. The attraction between an atom’s nucleus and its electrons is much stronger than bonds in a molecule. For example, the first ionization energy, or energy required to pull away the first electron, is 1312 kJ/mol for H and 1314 kJ/mol for O. So you can put enough energy into the atom such that one of electrons get energetic enough to escape the pull of the positive nucleus. Now you have an ion, the beginnings of a plasma.


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