L: Can two hydrogen atoms stick together, like H₂0 but without the oxygen?
K: that’s an interesting question. How did you come up with that?
L: Well, hydrogen only has one electron and would want one more. So I think two hydrogens could share with each other.
K: I eventually told him he was right, after double checking on google. I don’t trust myself to remember high school chem lol.
- K, May 28.
One of the things that I love is when children arrive at conclusions based upon what they understand and know and make guesses accordingly. It could be argued that the entire of science¹ is exactly this pursuit, except with more money and fancier toys.
Contained within these four lines of dialogue, is indeed the central questions which underpin chemistry and when I saw this on Facebook, my next line of enquiry is to task the very next question which underpins the entire of science¹ - why?
If I can not find out 'why' and put it in simple terms, then I will have failed in this excercise. Or to quote Ernest Rutherford, the father of nuclear physics:
"An alleged scientific discovery has no merit unless it can be explained to a barmaid."
- Ernest Rutherford (allegedly)
So then, without further adieu, here goes nothing. Kaboom.
The biggest single force (if you want to call it that) in the universe, even bigger than the forces of gravity, magnetism, the weak nuclear force and the strong nuclear force, is the drive towards entropy. Everything in the universe and that probably includes time, tends to flow from a state of higher energy to a state lower energy and the difference is transformed into stillness and weak heat. When you couple that with the theory which suggests that the universe itself will tend towards a quiet and boring heat death and where black holes and space-time will evaporate into a state of absolute boredom, that means that there is an awful lot of entropy going on.
Entropy is sometimes likened to 'disorder' (that is that everything starts out ordered and gradually falls apart) but I like the other idea that unifies chemistry and physics which says that entropy is just another form of 'laziness'. Entropy is just an advanced form of inertia, where objects are lazy and like to keep on doing what they are already doing until they are forced to change.
Almost all of chemistry is rearranging atoms and molecules into different things, which either costs energy to do so or gives off energy and the results are more lazy. Laziness is the key to understanding why there are diatomic homonuclear gases (diatomic = two atoms, homonuclear = the same kind of chemical).
On the very right hand side of the periodic table are the 'Noble Gases'. Noble is a nice way of saying that they don't react to much. Actually, they're just really snooty and smug and full of themselves and have no need to react to much. For reasons¹, all of the other kids in the period table want to look the Noble Gases because of how cool and non-reactive they are. Everyone in the periodic table has electrons which are filled up in shells and while there is a good explanation¹ of how and why they work, the short answer is that everyone wants to wear the clothes of the cool kids.
Most of the kids in the periodic table are very metal and like to hang around with themselves. They're also pretty dense and too ignorant to work out how to do chemistry with others. The kids on the far left of the table can be bullied out giving away their outermost coats and the kids who want them the most are on the far right²; and so are basically just like straight up thieves and will steal from others, which makes some salty chemicals.
As all of the kids are trying to be as lazy as possible, then they all want to do as little work as they can for the conditions. The most lazy and stable states can change depending on how hot it is outside or how much pressure they're under. Some kids like Sulphur have many different stable and lazy states which change based on what the ambient temperature is. It doesn't split into free sulphur atoms; it changes into a different state which is most stable under those conditions.
The thing is that all of the atoms except for the Noble Gases (because they are so cool) get really anxious and agitated if they ever find themselves alone. They all hate being by themselves and will want to find a buddy, even if their buddy steals their stuff.
Finding a buddy who either steals your stuff, or someone who shares your stuff, or even a whole bunch of buddies all being very metal and sharing everything together, is called a bond. Forming bonds with each other is how atoms to form molecules, which are more stable than if they were all alone.
Hydrogen is a perfect example. Lonely unbound hydrogen doesn't exist on earth, almost all of it is in a bound state. Water and most organic molecules contain Hydrogen. Hydrogen is really needy and looks for approval all of the time and wants to give away its one electron just so someone will be its friend. Even when there are two hydrogens hanging out with each other and someone bigger who can bully them both comes along, they will both break away from each other and give their electron to the bully. That's what caused the Hindenberg tragedy³. Hydrogen is really unstable; a single spark can set it on fire or cause an explosion, depending on how pressurized it is.
Because atoms don't like to hang around by themselves and chemistry happens which frees up single atoms, they often want to form pairs. The diatomic state of that atom is much more stable than the lonely unbound state.
It isn't necessary that all atoms tend to a diatomic state. The reason why any atom binds with other atoms is to tend to a stabler state. Gold exists in the free state because it is highly stable, and gold atoms do not find a state of lower energy very often, although there are certain gold compounds too.
It just happens that after some chemistry has been done, the atoms which are most likely to become lonely, are the bullies. Since chemistry happens with loads and loads and loads of atoms, then because there would be so many lonely atoms, they will just buddy up with whoever is free and that usually means other atoms just like them.
Under normal temperature and pressure that people like to live in, there are only seven kinds of atoms which will form gases (well, actually six but the seventh doesn't need that much more heat and pressure). Those seven elements are:
Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine and Iodine.
The short answer as to why you get diatomic gases is that atoms don't like being lonely and want to bind to other atoms to form molecules to achieve a state of lower energy and become lazier. It is not always necessary that they tend to a diatomic state; it is governed by external factors too.
¹science! which is beyond the scope of this post.
²which looks suspiciously like politics too.
³oh the humanity.
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