The periodic table - the list of all of the elements known - can be found on the walls of any science classroom.
The first and simplest element is hydrogen. It consists of a single electron orbiting a single nucleus. It is also the most abundant element accounting for more than 90 per cent of the atoms in the universe.
How do we know this? The answer is through a variety of observations and techniques astronomers have applied to studying the sky over the past several thousand years.
Most of the information we have about the universe has emerged in the past 100 years with the development of large telescopes, radio wave astronomy, X-ray telescopes, and infrared observatories. Unlike ancient astronomers who had only the naked eye, we can look at the universe across the entire electromagnetic spectrum.
Different elements behave in different ways at different wavelengths. We can determine the presence of elements by examining the complete spectrum and "see" their fingerprints in the way they interact with radiation at different energies. We can even determine relative and absolute quantities.
This is why we know the next most abundant element in the universe is helium and between them, hydrogen and helium represent about 99 per cent of all atoms. The rest of the periodic table is just one per cent of all that we can see.
If hydrogen and helium atoms were the only things in the universe, though, it would be a pretty boring place. By themselves, atoms don't do much at all. It is when atoms get together to form molecules things get interesting.
The simplest of all molecules is "hydrogen" or dihydrogen or H-H. It is sometimes confusing that chemists use the name hydrogen for both the element itself and its molecular form. We should really refer to H-H as molecular hydrogen but since single hydrogen atoms are a rarity in nature, we use the terms interchangeably.
That said, molecular hydrogen is a very simple molecule. It consists of two nuclei bound together in a common molecular orbital containing two electrons. (Technically, the ionized form of the molecule is even simpler in that it has only one electron in the molecular orbital but it is also a cationic species.)
The formation of molecular hydrogen occurred very early on in the universe - well over 13.4 billion years ago. The formation of molecular species was probably critical to the eventual clumping of matter into stars and galaxies as the molecular species would be heavier than single atoms resulting in gravitational attraction.
In any case, we can see both atomic and molecular hydrogen throughout the universe. Just as each element has its own set of fingerprints in the electromagnetic spectrum, so do molecules. If you know where to look, molecular hydrogen sticks out like a sore thumb.
As our understanding of the universe developed over the past century, we began to see that there are other molecules to be found throughout space. Stellar nebula, nascent solar systems, and even our own solar system contain a plethora of species.
For example, the very simple molecule hydrogen cyanide or HCN can be found in interstellar gas clouds. It can form in a number of ways and is often associated with a similar species, HNC or hydrogen isocyanide, which is not a common species on Earth.
The discovery of hydrogen cyanide in interstellar gas was quite exciting for astronomers and for biologist. Hydrogen cyanide is a building block molecule for other more complex species, including the nucleic bases. The universe is rich in the molecular precursors to the fundamental building blocks for life.
On Aug. 11, 2014, astronomers released a detailed study on the distribution of HCN, HNC, formaldehyde, and dust within the comae of two comets, C/2012 F6 (Lemmon) and C/2012 S1 (ISON). They obtained this analysis using the Atacama Large Millimeter/Submillimeter Array, a radio telescope.
However, the orbiter Rosetta and the Philae lander have gone one better in studying Comet 67/P.
Scientists examining the data from the mass spectrometers on the lander have discovered 16 identifiable molecular species on the comet's surface. Some even contain nitrogen giving rise to molecular species that could be building blocks for much more complicated molecules.
In particular, methyl isocyanate, acetone, propionaldehyde, and acetamide were detected for the first time as part of a comet's chemical make-up. Furthermore, the scientists were able to detect the presence of sugars on the comet's surface. These are formed from formaldehyde by bombardment with solar radiation.
Most scientists believe that comets are the remnants of the early solar system. They are leftover pieces that never found their way into joining with the planets. The chemical composition found on the surface of comets is expected to be the same as the proto-planets.
By all accounts, they are rich in the chemical building blocks that lead to more complex molecules and eventually, you and me.
