100 Nano-Stories: sp² Properties & Carbon/Graphene Aerogels!
Episode #97: sp² Properties and Delocalized Pi Bonds!
Preface! ✨
It’s your favorite material science & nanotechnology enthusiast! Today, we will cover the properties of sp² Hybridization and introduce carbon/graphene aerogels!
The link to the previous article is here:
TL;DR → sp² & sp³ Hybridization! 🔑
- The element we are using for this experiment is a carbon (C).
- Carbon has 4 electrons to share, or 4 electrons in its outer shell (4 valence electrons). Carbon wants to bond with exactly 4 other atoms to share these 4 electrons. It can create up to 4 bonds.
- Hybridization → Combining two things (subshells) to make one new thing (hybridized orbital).
- In sp³ hybridization for carbon, it uses all 4 valence electrons to become hybridized and become degenerated.
- In sp² hybridization for carbon, it uses 3 of the 4 valence electrons to become hybridized, leaving the P (z-axis) orbital unhybridized.
- Hybridized Orbitals make sigma bonds (σ) and Unhybridized Orbitals make pi bonds(π).
- Because the electrons are negatively charged, and as charges repel, they want to get as far away from each other. In sp³ hybridization, the angle between the electrons is 109.5°. In sp² hybridization, the angle between the electrons is 120°.
- Hybridization occurs when the carbon bonds with the S and P orbitals, but there is a problem. The P orbitals have more energy than S orbitals, so there is an imbalance of energy. To have the electrons equal the same energy (degenerate), we have to combine them (hybridize them) to a more stable energy level.
Authors Note:
This was an overview of the previous article. If you are left confused or want to know why the mechanisms work behind solid structures, I highly recommend reading the article above for detailed information! 🙏🏽
TL;DR complete! Let’s jump into today’s topic! 😄
sp² Properties! 💡
Well, what does an sp² hybridized orbital in a carbon atom look like? Well, for starters, we need to know how many valence electrons carbon has. The valence electrons are important because they tell us how many covalent bonds can carbon make.
In this case, Carbon has 4 valence electrons. The outer/last shell of carbon can hold 8 electrons, and this means we need 4 more electrons to fill the outer shell, so we need 4 covalent bonds.
Valence Electrons → Electrons in the outer shell/last row of an atom.
Covalent Bond → Shares a pair of electrons with another atom (via chemical bonding).
For those who need a reminder, this is the electron shell of a carbon atom:
However, hybridization will occur in a carbon molecule, due to the imbalance of quantum energy levels in the electrons.
Hybridization → Combining two things (subshells) to make one new thing (hybridized orbital).
We know that hybridization occurs when the subshells that hold the electrons of the carbon atom combine.
But why do some atoms go under sp² or sp³ hybridization, Carlos?
The specific hybridization depends on the number of atoms/covalent bonds that are attached to the carbon atom.
In sp² hybridization, there are 3 atoms attached to a carbon atom. For example, take a look at the number of atoms/covalent bonds attached to the carbon atom in a molecule of ethylene.
Since there are 3 covalent bonds per carbon atom, this means that 3 of the 4 valence electrons (in each carbon atom) will undergo hybridization to create the covalent bonds.
Since 1 of the electrons (of the outer shell) in each carbon atom will not undergo hybridization, that electron will create the double bond between the carbon atoms (a pi bond), which results in sp² hybridization.
If a carbon atom has 4 atoms attached to it, it’s an sp³ hybridization. 0 pi bonds will form.
If a carbon atom has 3 atoms attached to it, it’s an sp² hybridization. 1 pi bond will form.
If a carbon atom has 2 atoms attached to it, it’s an sp¹ hybridization. 2 pi bonds will form.
Author’s Note:
My apologies, reader. I didn't add this in Episode #96 because there was a lot of information to give. I wanted to give you the mechanisms first, and then explain why the specific hybridization number occurs, but it should have been the other way around. Please forgive me. 🙏🏽
Why sp² Hybridization? 💡
Okay, that’s nice Carlos, but why should I know about sp² hybridization? What’s the point?
sp² hybridization has that pi orbital that was left unhybridized because there were only 3 atoms attached to a carbon atom.
But in certain molecules/materials, like benzene or graphene, the pi bonds are delocalized.
If a pi bond/electron is delocalized, it means that the electron can move freely and pi bonds can overlap to create electrical conductivity. This electrical conductivity allows us to create carbon and graphene aerogels! 🎉
How Does Delocalization Work in sp²? 🔑
However, this is possible as long as the chain of carbon atoms continues forever.
The reason why the carbon atom chain has to continue is that carbon has the pi bond that can bond to other pi bonds, and if the atom isn’t a carbon atom, the chain ends (because it doesn’t have pi bonds to overlap with other pi bonds).
An analogy to the pi bonds can be a river with 5 doors.
The molecule is the river. The Carbon Atoms are the 5 doors. Each Pi Bond is the water.
Since there are 5 carbon atoms, we have 5 pi bonds.
These doors control if the water can continue flowing throughout the river. If 1 of the 5 doors isn’t open, water can’t pass, and water can’t continue flowing. If all the doors are open, water can pass and continue flowing.
If we apply the analogy to the carbon atoms, we can say that if one of the atoms that bond to the molecule isn’t carbon, the pi orbitals can’t overlap, so no electrical conductivity. :(
If all the atoms that bond to the molecule is carbon, then the pi orbitals can overlap and produce electrical conductivity. :)
Delocalization Examples! 🔑
Here is an example where the chain of carbon atoms/pi bonds fail. Hydrogen is chemically bonding with carbon atoms, so the pi bonds cannot overlap.
Here is an example where the chain of carbon atoms/pi bonds is continuous forever. The Carbon atoms are chemically bonding with each other, and it allows for the pi bonds to overlap with each other, allowing for stronger pi bonds and electrical conductivity.
Author’s Tip:
Notice that the “lines” are the covalent bonds. The lines determine which atoms are bonded with each other. If all the lines point/end at a carbon atom, then you have delocalization and pi orbitals overlap (touch each other). If even one line doesn’t end at a carbon atom, the pi bonds fail to overlap. Hope it helps! :)
If all the carbon atoms are bonded to each other (or the lines touch the Carbon atom only), the pi orbitals overlap and create a circle around the carbon bonds (aka sigma bonds).
Here is a visual example of the overlapping of pi orbitals in a benzene ring:
Closing Thoughts! 💭
So, if sp² hybridization gives us materials with electroconductivity, what good is it?
Can we make materials that can be used for supercapacitors? Batteries? Insulators? Hydrogen Storage?
Idk, you will have to wait for The Beginning of Carbon & Graphene Aerogels! 😀
Also, I can’t believe I am 3 episodes away from finishing an iconic digital book! It’s been an amazing journey! Shoutout to my followers since the beginning (and the new followers of course!) 😁
See you soon to introduce (1,3-dihydroxybenzene) and formaldehyde, aka. . .
🎉 Carbon and Graphene Aerogels! 🎉
Vocabulary! 📓
Sigma Bonds → Head-to-head overlap of atomic orbitals. The symbol for sigma is (σ).
Pi Bonds → Lateral overlap of atomic orbitals. The symbol for pi is (π).
Hybridization → Combining two things to make one new thing.
Valence Electrons → Electrons in the outer shell/last row of an atom.
S Orbital → Contains two electrons and their orbitals are shaped like a soccer ball.
P Orbital → Contains one electron and their orbitals are dumbbell-shaped. They are classified into x-axis, y-axis, and z-axis depending on their orientation.
Subshell → Holds orbitals/a certain number of electrons (probability of where electrons can be). S subshells hold up to 2 electrons, and P subshells hold up to 6 electrons.
Degenerate Orbitals → Orbitals with electrons that contain the same energy as each other.
Orbital → A region where you have a high chance of finding the electron(s).
Covalent Bond → Shares a pair of electrons with another atom (via chemical bonding).
Decloalizaion of Pi Bonds→ The electron can move freely and pi bonds can overlap across more than two atoms/nuclei.
Bonus Resources! 💻
Previous “100 Nano-Stories!” 🔖
© 2021 by Carlos Manuel Jarquin Sanchez. All Rights Reserved.
