The versatility of semiconductors has allowed significant advancements in technology. Their size and bonding and antibonding orbitals influence how they behave. Unlike metals, semiconductors have an energy gap that allows their electrical and thermal conductivity to be manipulated. Understanding how semiconductors behave opens a world of possibilities when it comes developments in technology.

Think about how our lives would be different if we didn’t have a smartphone or a computer. 

In fact, without one of those, you wouldn’t even be able to watch this video!

Even in our lifetime, we have seen how much these electronic devices have evolved. Every year, the newest products are faster, smaller, and more efficient, and over time, they have become cheaper for us consumers to purchase. 

This progress was made possible because of semiconductors, and their reach extends beyond just phones and computers. They are used in household appliances, cars, and healthcare devices. 

But, what makes semiconductors so versatile and useful in all of these contexts?  The answer depends a lot on size AND on bonding and antibonding orbitals.   

Semiconductors are right in between the atoms like carbon and oxygen that we have talked about already that form covalent bonds, AND metals like iron and copper.  

As a quick review, atomic size relates to the strengths of bonds that the atoms form. The smaller the atomic size, the better the overlap of atomic orbitals to generate a BONDING molecular orbital that is lower in energy and more stable.

This means that in the context of bonding and antibonding orbitals, the energy gap between bonding and antibonding orbitals is large. 

Electrical current is a flow of charge, and the charge is carried by electrons. 

Conductivity occurs when the electrons in the bonding orbital get excited and move to the ANTIbonding orbital. This is why bonding orbitals get the name of “valence band”, and ANTIbonding orbitals get the name of “conduction band” in physics.

If the energy gap is large, again, it would be DIFFICULT for the electron to move from the bonding orbital - the valence band - to the ANTIbonding orbital - the conduction band.  

This is why NON-metals that form covalent bonds ultimately have difficulty conducting electricity. 

Knowing this information, what do you think is true of metals?

Metals are comparatively larger in size than non-metals, and the energy gap between the bonding and antibonding orbitals are extremely close in energy.  

In fact, they can be so close in energy that the electrons can move freely from the valence to the conduction band without needing to overcome an energy gap AT ALL. This is why metals are great conductors of electricity.

And here is where the beauty of semiconductors comes in.

In comparison to metals and non-metals, semiconductors are intermediate in size, and they make bonds that have a SMALLER energy gap than NON-metals to be able to conduct electricity. 

However, the presence of an energy gap, which is NOT present in metals, gives them the versatility so that they can be manipulated to have various conducting properties.  

So, it is not a surprise that semiconductors have great value in modern technology, and knowing some fundamentals of chemistry helps us to better understand this complicated topic.