100 Nano-Stories: Sigma & Pi Bonds!

Preface! → ✨

It’s your favorite material science & nanotechnology enthusiast! A couple of days ago, I explained how to decipher and name alkanes, alkenes, and alkynes! I recommend you read them briefly because you will need the knowledge in the articles to understand today’s lesson!

But for today’s topic, I want to discuss sigma bonds, pi bonds, and how they relate to organic chemistry & aerogel research! A lot of students can make a mistake in this situation, so it’s better to clean up those mistakes now than later!

Enough talking! Let’s just jump right into it!

Sigma v Pi Bonds!→ 💡

But What Do They Mean? → 🤔

In organic chemistry, bonds like single bonds (alkanes), double bonds (alkenes), and triple bonds (alkynes) have bonds that can head-to-head overlap or laterally overlap between atomic orbitals.

Sigma Bonds is the head-to-head overlap of atomic orbitals. If you had a model of a sigma bond, you could rotate it. The symbol used to describe a sigma bond is “σ”.

Pi Bonds is the lateral overlap of atomic orbitals. If you had a model of a molecule with pi bonds, you can’t rotate it around. The symbol used to describe a pi bond is “π”.

Sigma → Head-To-Head Overlap. Pi → Lateral Overlap.

But how do we determine sigma bonds and pi bonds in alkanes, alkenes, and alkynes, Carlos?

  • If you have an alkane (single-bond), you will have 1 sigma bond (1 σ), and 0 pi bonds (0 π).
  • If you have an alkene (double-bond), you will have 1 sigma bond (1 σ), and 1 pi bond (1 π).
  • If you have an alkyne (triple-bond), you will have 1 sigma bond (1 σ), and 2 pi bonds (2 π).

Example Time! → 💡

Example 1! → 🔑

Let’s do 2 examples for this article! I will do more examples in the next article!

This is an alkene! But if we notice, there are four single bonds and one double bond! From our definitions, a single bond only has 1 sigma bond (1 σ). But a double bond has 1 sigma bond and 1 pi bond (1 σ, 1 π).

Since there are four hydrogen atoms, that means there are 4 sigma bonds (4 σ) plus the double bond of 1 sigma bond and 1 pi bond (1 σ, 1 π).

The final answer is 5 sigma bonds and 1 pi bond (5 σ, 1 π)! 🔑

Example 2! → 🔑

For those who are confused about the “R”, it is an abbreviation for a methyl group. A methyl group can consist of CH3 (1 carbon atom & 3 hydrogen atoms).

So “R” → CH3.

OH is a hydroxyl group.

But now that we know what these letters mean, let’s solve for sigma & pi bonds!

In the double bond, 1 sigma bond and 1 pi bond exist connecting the carbon atom to the oxygen atom (1 σ, 1 π).

In the bond connecting OH, there are 2 sigma bonds (2 σ): 1 connecting it to the carbon atom, and another one connecting O to H.

In the bond “R”, (a.k.a. CH3), there is a carbon atom and 3 hydrogen atoms, all single-bonded. This means that these 4 atoms will attach to the main carbon atom, and we end up with 4 sigma bonds (4 σ).

Time to add up all the sigma & pi bonds! We have (4 σ) from “R”, (2 σ) from OH, and (1 σ, 1 π) from the double bond!

The final answer is 7 sigma bonds and 1 pi bond (7 σ, 1 π)! 🔑

Closing Thoughts! → 💭

This was a lovely introduction to more topics that certain students may get confused about! I’ll be back tomorrow with another round of common mistakes students may do in organic chemistry!

Vocabulary! → 📓

Alkanes → An organic compound that is only made out of carbon & hydrogen atoms, only single covalent bonds.

Single-bond There is two electrons (or one pair) being shared between two atoms.

Double-bond There is four electrons (or two pairs) being shared between two atoms.

Alkenes → Double Bonds occur between carbon atoms in a molecule in organic chemistry.

Alkynes → An organic compound that is only made out of carbon & hydrogen atoms, only triple covalent bonds.

Triple-bond → There is six electrons (or three pairs) being shared between two atoms.

“R” → CH3, a methyl group.

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).

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© 2021 by Carlos Manuel Jarquin Sanchez. All Rights Reserved.

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