Why Chemistry Is Awesome | Episode 2: Tin – From The Bronze Age To Touch Screens

In 4500 BC, in a small village located in what is now Pločnik, Serbia.
Neolithic Vinca metallurgists produced the first known example of our species’ first technological breakthrough: Bronze.
Bronze, being a much stronger material replaced stone throughout Europe by 3100 BC, ending the stone age that lasted over three million years.
This was made possible by the unique characteristics of Tin.
Bronze is an alloy meaning it is a material made with multiple metals.
And ancient Bronze was copper with around 6-10% tin mixed in.
This made the material much stronger than copper or Tin on their own.
You see, the atoms in all pure metals are take form of repeating lattice structures.
This causes the material to have areas of weaknesses called slip planes.
When a strong enough force is applied to the metal, the atoms along the slip planes move, which is why metal is moldable.
But when you mix in Tin with copper, it acts like mortar and reinforces copper’s slip plane, making it a harder material.
Tin’s low melting point of 231.0 degrees Celsius allowed it to be accessible in the Neolithic period compared to iron with a melting point of over 1,500 degrees Celius.
It is because of the characteristics of Tin, one of the most historically important alloys ever known was possible.
Iron eventually replaced Bronze as the dominant material, but the story of Tin’s contribution to society has two remaining highlights.

And this takes us to 1795 to the French Revolutionary Wars.
French troops were fighting battles in Italy, Germany, and all the way in the Caribbean, and providing stable sources of food for soldiers became a challenge.
French government led by Napoleon created the Food Preservation Prize, which offered 12,000 francs to anyone who could improve the process of preserving food.
This ultimately led to Peter Durand’s patent for the tin can.
The first cans were made from steel or cast iron and were plated with Tin because of its corrosion-resistant properties.
The invention of the Tin Can seem simple today, but it revolutionized how we preserve food, and Tin played an essential role.
Now fast forward to release of the original iPhone in the summer of 2007.
As we all know, that device revolutionized how we interact with computers, information, and each other.
Indeed, touch screen technology played a huge role in that revolutionary experience.
Tin is part of an extraordinary compound called Indium Tin Oxide or ITO.
ITO is unique because it possesses two qualities needed for touch screens.
One, the material has to be transparent so that the light from the LEDs can pass through.
And two, the material also needs to be highly conductive so that it can facilitate an electric field.
When you tap on a touch screen, the ions in your finger disrupts the electric field and is precisely registered by the sensor apparatus.
Materials like ITO that are both transparent and highly conductive are scarce.
It all boils down to its Electronic Band Structure.
The electrons in atoms orbit its nucleus at various distances based on energy levels, the key term here is orbital.
Orbitals are like steps on a ladder in the sense that it takes energy for electrons to climb from one level to the next but cannot maintain in orbit in between the levels.
As atoms bond together and form molecules in solid materials, the orbitals of each atom overlap with one another, forming valence bands and conductive bands.
The electrons in the valance band are bound to their respective atoms; however, the electrons in the conductive bands are free to move around.
The space in between the bands is called the energy gap.
The larger the gap, the more energy it takes for electrons from the valance band to move into the conductive band, making it a good insulator like glass and diamonds.
Naturally, the smaller the gap, the more conductive the material-- in metals for instance-- the valence and conductive bands actually overlap.
For a solid to be transparent, its energy gap needs larger than the energy in visible light.
Indium Oxide has an energy gap wide enough to be transparent, and ITO is formed by replacing about 10% of the indium atoms in indium oxide, with tin atoms.
This process is called doping and it amazingly allows ITO to be almost as conductive as metals at the same time, maintaining the energy gap for transparency.
You see, each tin atom naturally has one more electron than an Indium atom, so doping Indium Oxide with Tin adds electrons to the material.
Tin has played an essential role throughout history.
And its story proves to be another example of why chemistry is awesome.
Music Credit: Marxist Arrow by Twin Musicom is licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/...)
Artist: http://www.twinmusicom.org/