The Many Faces of Hydrogen

Hydrogen is the most fundamental element in the universe, and the most ubiquitous too. On the periodic table it's often a lonely island because no other elements are remotely similar to it. It's just one electron orbiting one proton, that's how lonely it is.

This is hydrogen:

₁H - if you put it next to the alkali metals, it would be odd seeing it amongst the more reactive solids. So instead it's completely isolated, and that suits it best.

Hydrogen has no neutrons in it's most common form, H-1. It's also called protium, but I'll be calling it hydrogen for the rest of the blogpost, it's that ubiquitous. This is an oddity for most atoms, as neutrons are the stabilising force in an atom that ensure it doesn't fall apart. Protons repel each other, they're all positively charged, and the very large nuclear force between protons and neutrons helps ensure they stick together. H-1 is thus quite unique, though its solitary proton means there's no repulsion that will occur either way.

Let's say we were able to add a neutron to an H-1 atom, and we formed an H-2 atom. We now have heavier hydrogen, which has one proton and one neutron. This is deuterium, and has an abundance of about 0.0156% - and it's also stable. Sometimes deuterium will appear in "heavy water", where there are H-2 atoms instead of H-1 atoms - it's occasionally referred to as D₂O. I may as well mention that deuterium is an isotope of hydrogen, which means that heavy water will indeed be heavier (who knew?) but it's chemically the same (neutrons have no charge, after all). You'll find heavy water in nuclear reactors as it can slow down any neutrons that are emitted for nuclear fission, and I'll describe it later.

Add another neutron, and we get tritium, or H-3. This time round, it's radioactive and has a far, far smaller abundance than hydrogen. In fact, here's a nice graph detailing how different their abundances are:

Tritium is naturally produced through the reaction of nitrogen gas with cosmic rays in the atmosphere, though it can also be produced in a nuclear reactor such as those in a nuclear missile. This is a result of nuclear fission, which would see an emitted neutron strike a deuterium atom, hence the extra neutron. Should tritium react with oxygen, you get tritiated water which can cause cancer if consumed. This is due to the aforementioned radioactivity - it will emit a beta particle to form a He-3 atom, and beta radiation is ionising. It can thus also be used as a radioactive tracer to resolve seepage issues in dams and power stations by noticing why water may be leaking.

Beyond this point, there are no more naturally occuring isotopes, and you'll need to increase the number of neutrons present. However, these isotopes are increasingly more unstable so will instead spit out the neutrons stuffed into it - their half lives are astonishingly small (tritium's is 12 years, and H-7 has a half life 32 orders of magnitude smaller). The largest isotope scientists have managed to synthesise is H-7, most likely out of the sheer joy of the subject as they will never catch on amongst the general public. Perhaps you'll manage to make a hydrogen isotope as heavy as a lithium atom one day. 

(Briefly mentioning) fission and fusion

When you split an atom, it undergoes nuclear fission - you fire a neutron at a heavy nucleus and it causes it and other atoms to break apart in a chain reaction, generating energy. However, isotopes of hydrogen are used in nuclear fusion, which is where two atoms are joined together. 

Should you fuse a deuterium atom and a tritium atom, you'd end up forming a helium-4 atom and an emitted neutron, like in this equation:

³₁ H + ²₁ H → ⁴₂ He + ¹₀ n

This in turn releases energy as E = mc² would tell us - the two atoms fused together and formed an atom of lower mass; the missing mass has now become energy. This is what the Sun does in its core and is how we end up with increasingly heavier elements. It's also what occurs in fusion reactors which are slowly becoming able to power many kettles, and it's also what occurs in the explosion of hydrogen bombs (along with fission). 

It's easy to forget that the most common form of hydrogen is merely one of three natural isotopes, probably because you never encounter the other two most of the time. However, the other two play a key role regardless in our lives and potential deaths.