I've about decided that presenting my outline of knowledge isn't the best way to generate interest in the subject of independent learning, so I'm going to try something else. In my college course in Chemistry back in the 1970s, I was particularly interested in what it said about the relative abundance of the elements in the universe.
I don't have the tools to reconstruct the natural abundance of elements from principles of nuclear physics, as some physicists have done, but I have managed to find a few tables of abundances of the elements in the solar system. I'm not sure which is considered the "best" or most current information; I'm still looking for it.
For a couple of days I've been working on making a list of molecules or compounds that can be made from these elements. There are quite a few that can be made in the low-density, high-energy environments of interstellar space, but I'm more interested in those that survive in an earth-type environment. I'm also interested in those that are chemically active.
Hydrogen has the lightest and simplest atoms, and is the most abundant of the elements. I'm not sure whether most of it is collected in stars or in free space, but there are three important forms of it. At highest temperatures, it is disassociated into its components, protons and electrons, and is found in the form of plasma. At cooler temperatures, and in most of interstellar space, it is found in the form of hydrogen atoms. At earth-type temperatures, it is found in molecular form, H2. At very low (cryogenic) temperatures, it can be liquefied, and solidified. However, such very low temperatures appear to be uncommon in the universe. There may be a metallic form found at extremely high pressures such as in the interior of Jupiter.
Hydrogen is substantially lighter than the other elements of earth's atmosphere and not only tends to float above the other gases, but its molecules can achieve escape velocity in the upper atmosphere. It only exists on earth because it can be chemically bound to other atoms, but that's another story. In order for it to be used as fuel, it has to be first pried out of these other molecules, which presents a considerable practical disadvantage for advocates of a hydrogen economy.