Ordinary hydrogen consists of a single proton, which has a positive electrical charge, with a negatively charged electron “orbiting” it. The proton makes up the nucleus of the hydrogen atom. The electron weighs almost nothing compared to the much more massive proton, and the mass of this lone proton is generally denoted as approximately 1 Atomic Mass Unit (1 AMU). Meanwhile the atom has a net electric charge of zero because the proton and electron have opposite charges.
If you add an uncharged neutron to the mix, you just about double the mass of the atom, since neutron and proton masses are almost identical, so you have a 2 AMU nucleus. Since the neutron is uncharged, you still need just the one electron to keep the atom electrically neutral. The proton and neutron together make up the nucleus of this configuration.
What you have is still hydrogen, but it’s twice as heavy, so the chemical behavior will end up being noticeably different, unlike most cases where larger atoms might have an extra neutron or two. (For example there is no significant difference in chemical behavior between a uranium atom with 92 protons and 143 neutrons, and one with 92 protons and 146 neutrons–the weight difference is barely 1 percent rather than 100 percent.) The just-a-proton hydrogen is called hydrogen-1, 1H, or protium while the heavier proton-and-a-neutron hydrogen is called hydrogen-2, 2H or deuterium. Physicists even informally give deuterium its own chemical symbol, D. (Officially, it’s a no-no to do this.) When talking about just the nucleus of deuterium, it’s called a deuteron, and the study of deuterons is deuteronomy.
What, you thought this was going to be an article on the Bible? Check the date of this post!
As you can see from the above diagram, there is also a two neutron configuration called tritium but it’s off topic for this post.
Deuterium makes up about one hydrogen atom out of every 6,420 or so, and it is believed that most deuterium that is around today was made during the Big Bang. This is because, even though it’s stable (not radioactive) it’s fragile and will break up easily under the conditions deep in the cores of stars–or be consumed as part of the chain of events that fuses hydrogen into helium, which is what powers most stars including our sun.
We have plenty of hydrogen on earth, but it’s not in the form of elemental hydrogen gas. Rather, much of it is bound with oxygen in water molecules, two atoms of hydrogen for every one atom of oxygen, H2O. And some of that hydrogen will be deuterium. Of course most of the time only one of the two hydrogen atoms is deuterium.
Physicists can concentrate the deuterium-bearing water, and ultimately get large quantities of deuterium oxide, heavy water, or D2O. Instead of having a mass of 16 (from the oxygen) plus 2 (for the two protium atoms) = 18, it ends up with a mass of 16 + 4 = 20.
I mentioned chemical differences. Well one chemical difference is that heavy water has stronger “hydrogen bonds” between the molecules than regular water does–the strength of the bond ultimately depends on the mass of the nucleus of the hydrogen atom–and thus it takes more energy to break those bonds to melt and boil heavy water. Instead of melting at 0 degrees Celsius (32F) it melts at 3.8C or 39F, and it boils at 101C or 214F (instead of 100C/212F). (Of course that boiling point applies down in the swamplands at sea level, not up here in the high plains and mountains.)
This difference is highlighted in this video from Thunderf00t:
In the video, note that he demonstrated by experiment (so even a Creationist can’t deny it!) that heavy water ice is heaver than regular (protium oxide) water, rather than being lighter. It is of course still lighter than liquid heavy (deuterium oxide) water.
I hope you found this interesting; if not well then…