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Roger Weller, geology instructor
by John Welter
Boron Ain’t So Borin’
Boron is the 5th element in the periodic table. Meaning
it is characterized by having 5 protons and 5 electrons. It holds a place on
the Table next to Carbon, Nitrogen, Aluminum and Silicon, and to be frank, we’ve
all overlooked this element. So, why do we care? What if I told you pure Boron
crystal (which can only be made in a lab) is the second hardest known material
just behind diamond at 9.5 on the Mohs scale of hardness? What if I told you
that Boron is essential for plant life? What if I told you that there was still
much more to this exotic element. So let’s explore Boron; its history, its
chemical properties, how it’s made and used. Hopefully next time you scan
through the periodic table your eye will dwell on Boron just a little bit longer
because “Boron Ain’t So Borin’”.
The Chemistry Stuff:
Here is a listing of some of the important chemistry information about Boron
Atomic Number: 5
Atomic Weight: 10.811
Density: 2.37 grams/m3
Period #: 2 Group #: 13 (A3)
Melting Point: 2348 K (2075ºC or 3767ºF)
Boiling Point: 4273 K (4000ºC or 7232ºF)
Room Temperature State of Matter: Solid
Elemental Classification: Semi-metal (metalloid)
Electron Shell Configuration: 1s22s22p1
Known Isotopes: B10-B17 (19.9% B10) (80.1% B11)
Joseph-Louis Gay-Lussac Louis Jaques Thenard Sir Humphry Davy
Before the introduction of modern chemistry, Boron was found
naturally in its compound form, Borax and Kernite. These compounds are a
strange white powder found in what is now Turkey. In fact, Boron is derived
from the Arabic word “boraque”, which means white. Modern day texts don’t seem
to agree on how or if Boron was used in ancient times. For now there seems to
be no proof. However things would change in the 1800s when modern chemists
would begin their search for “atoms”, the building blocks of all things.
Although Greek and Indian philosophers theorized that there must be small things that makes up all things in existence as early as 600 BCE. It was not until the 1800s that Europeans found proof that all matter are made of either elements or compounds, which are a combination of elements. So chemistry was born and the hunt for fundamental elements began. It was not long before French chemists had a list of some of these naturally occurring and common elements; hydrogen, Azote (Nitrogen), Charcoal (carbon), iron, and mercury were among them. In just a couple of years scientists discovered a few methods for separating some compounds into their individual elements. Electrolysis used electricity to separate compounds or sometimes acids could be used. This is where the story of Boron begins because before this time Boron had never been separated from its natural compound borax. And in 1808, the French chemist duo composed of Joseph-Louis Gay-Lussac and Louis-Jaques Thénard theorized that Boron was one of the elements that chemists were looking for. It took little time for English chemist Sir Humphry Davy to isolate Boron using acids to confirm the French duo’s theory. Boron was finally confirmed as an element. However, Boron seemed to have no special quality that made it valuable, so chemists spent little time studying Boron and moved on to find more elements. In time, Boron faded from the spotlight. Yet, there were still some strange discoveries to be made about Boron…
Where does Boron Come From?
This question has a
simple answer and a more complex answer. First answer and the simple answer is
related to where Boron is found on Earth. The second part of where Boron comes
from is related to its unusual cosmic creation.
Naturally occurring Borax is
found in only a few countries. Turkey is the leader in Boron reserves around
the world, but Russia, the United States and China have significant reserves
also. Like mentioned before pure Boron is not found naturally. It is always
found in compounds of Borax (chemical formula: Na2(B4O7))
and Kernite (chemical formula: Na2(B4O6)) after
water has evaporated. Since this process requires places where great floods
occurred in the past to dissolve the Boron. Then later these flooded plains
evaporated and never had a chance to rehydrate, these compounds are only found
in super dry arid regions that were once flooded.
Next we have to take a step back. Really far back. So that we can answer the second part of where Boron comes from. Boron is unlike most elements because it is created through an entirely different means then 97% of the elements.
Boron (as well as Lithium
and Beryllium) is created through a process known as Cosmic Spallation. Cosmic
meaning related to the universe and spallation meaning a process where
collisions break up a nucleus of an atom. This process consists of cosmic rays
being shot out at incredible speeds and energies and ram into an atom. So a
larger element, say Carbon, will get smacked with these rare cosmic rays and
decay into smaller elements like Boron. This is the only known way of creating
Boron. This is accepted because in the 1970s particle physicists used
mathematics to confirm how heavy elements were formed inside stars. However,
there was no room in the equations for Boron or its cosmic collision brothers
Lithium and Beryllium. This also explains why Boron is so rare. Being created
in such an unusual way and in a process that does not happen on the same grand
scale as supernovae or stars, Boron is significantly less abundant than other
(only 3 of the 118 elements are produced through Cosmic Spallation)
The Strange Nature of Boron:
Nearly all of the material we see is a combination of two or more elements, known as compounds. Yet, elements follow specific rules so that they can become stable (otherwise they would simply decay or find another element it would prefer to bond with). Chemists found that elements within a stable compound are surrounded by 8 electrons to be stable (hydrogen actually only needs two because of its size). This is known as the “octet” rule. A Lewis-dot structure is a graphical representation that helps chemists visualize the balance of the compound, as well as to determine the shape of the compound.
For the both examples (CO2 and H2O), we can clearly see that each element has the necessary electrons to be stable. Carbon and Oxygen are surrounded by 8 dots and Hydrogen is surrounded by 2 electrons. We can also see that it is the electrons that determine the shape (CO2 is straight and H2O bent).
Here is where Boron’s
strange nature comes into play. Even though Boron wants to fill its electron
shell with 8 electrons like its fellow elements, it doesn’t always. There are a
number of examples where Boron simply breaks the “Octet” rule.
Above are two known examples of where Boron just ignores the “Octet” rule and chooses to have 6 valence electrons instead of 8. Still, Boron is not a trouble-maker by nature and prefers to completely fill its orbit with electrons. Boron Trifluoride, for example, would gladly add another fluorine atom and make itself an octet (BF4).
How do we use Boron?
Well originally Boron wasn’t used for much, but people have gotten pretty creative and found a number of ways to use Boron. As technology increased so did the notable ways we make use of Boron.
Here is a table that indicates how Boron is used today.
Boron is used in many fiberglass composites, for its strength and resistance to heat. The fact that Boron has few industrial uses also may play a part in its use because it is generally pretty cheap.
Just as with the Fiberglass
mixture, Boron adds strength and heat resistance to glass. Pyrex trademarked
the special heat-resistant Borosilicate glass in the 1915s and has been a hit in
the kitchen since.
One of the first major uses
of Boron was for fireworks. Boron gives off an eerie, unforgettable green glow
when burned. It was not long before chemists found a use for Boron in Fireworks
to create a dramatic, colorful explosion.
Space Rocket Ignition:
If you thought Fireworks were Boron’s only explosive job, you are wrong. Boron is used as the in NASA rockets because it is thermally stable, stable in a vacuum, and the burn rate is independent of the pressure. In short, Boron is safe and effective on Earth or in space.
Nuclear Reactor Absorption Material:
Nuclear reactors work by using a radioactive material to heat water. This water turns to steam and turns pistons that produce electricity. Yet we all know that radioactive material is dangerous. So instead of letting the majority of decayed particles fly around, scientists added rods that absorb the radioactive particles as the first line of defense against the dangerous substance. Boron is used to create a part called the Control rod, which absorbs excess particles (picture on the left).
Boron is also an essential part of all plants, so it is added to fields to ensure that the plants are healthy. In particular, Boron helps strengthen cell walls in plants. Boron can also be used as an insecticide and fungicide with relatively low toxicity (still not safe for direct consumption).
So, there you have it. The story of Boron. An unusual cast member in the periodic table. From strange beginnings, to everyday use Boron should not be overlooked. Remember, too, that this odd one is also essential for plant life, which is arguably essential for animal life. It has got us to the Moon and is pivotal in defending us from radioactive decay. So, without question “Boron Ain’t Borin’”
Jefferson Labs- It’s Elemental