01.24.10
Airbags, Explosives, Azides
Nitrogen gas (N2) makes up about 80 percent of the chemical cocktail we call air. Its colorless, odorless, relatively unreactive, and emotionally distant. But it’s these very properties that make nitrogen itself so useful.
Chemical bonds are made in a variety of ways, but stem from 2 basic ideas. Every atom (almost) wants to be surrounded by 8 valence electrons (electrons in the outermost orbital). This is known as the octet rule. Second is that the electrons themselves want to spread their existence over the largest possible area. These things determine how most molecules interact.
With this in mind let’s look at Nitrogen, Element number 7, and the fifth element in from the end of the periodic table, which means in it’s natural state it has 5 electrons in it’s outermost shell. It wants to have 8. Well if we put 2 of these nitrogen molecules together we get both the things we asked for in a bond. Each nitrogen molecule allocates 3 electrons to exist between the molecules, which adds 3 electron to the neighbor giving an octet to each. This means that there are 6 electrons spread out over a large area of 3 different bonds, one in the middle called a sigma bond, and two which bow out from that called pi bonds. The reason that there is not just a solid space of electrons connecting them actually has to do with interference in the clouds of electrons, creating areas of low electron density and high electron density. Remember an electron is not like a little ball, but like a smear of something throughout space. The more ambiguous the position of these electrons, the happier they are. Since they exist in these waves of probability, when the waves overlap, they interfere with each other.
These three bonds are additionally stabilized through something called resonance, meaning they can further smear themselves through space by jumping into empty orbitals on each nitrogen. Although they don’t want to do this naturally the very idea that they can adds to the overall stability of the gas.
With all these factors adding to a very happy and content gas, it raises a very interesting idea. It must take a lot of energy to break that bond. Those molecules are very happy, so pulling that bond apart would be a very difficult, endothermic process. Lots of heat and energy must be dumped into the system. This usually happens around 3000 degrees Fahrenheit. If this is true, then we can infer the opposite. When this bond forms it must release that same amount of energy and heat in a violent exothermic process.
So this is where we get things like azides, nitrous oxide, nitro glycerine etc. They take 2 nitrogens and bind them to something like oxygen, which turns to triple bond into a double bond. Then with very little activation energy, as in the case of azides in airbags, you allow the bond to the neighboring atom to break, releasing the nitrogen gas and letting of lots of heat in the process. Pictured above is a sketch of an azide reaction in progress. This is the reaction that takes place when an air bag in your car is deployed. The azide is attached to sodium and once the nitrogen gas is released, the sodium is neutralized with other agents. Sodium on its own is quite reactive as well.
