Reef Chemistry Question of the Day #286: Pi Day!

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #286

Today is March 14, pi day!

In honor of the day, we have a reef chemistry question about pi.

Which of the following chemicals contain pi bonds?

1. Nitrate, NO3-
2. Chloride, Cl-
3. Phosphate, PO4---
4. Calcium, Ca++
5. Ethanol, CH3CH2OH

Pick all you think are correct.

Good luck!

Previous Reef Chemistry Question of the Day:

Reef Chemistry Question of the Day #285: Aragonite vs Calcite

Reef Chemistry Question of the Day #285 Reefers often hear that organisms in their aquaria may deposit aragonite or calcite, but do not always pay attention to what those words imply. What is (are) the difference(s) between aragonite and calcite? A. Aragonite contains one carbonate ion for...

www.reef2reef.com

 

[KrisReef]

1,3,&5, just because I took chemistry twice and I feel like I should have paid more attention back then and I am glad that the op did.
Happy Pi Day RHF. Thanks for the quiz!

 

[BZOFIQ]

its 3, 1 & 4 or 3.14

 

[Randy Holmes-Farley]

And the answer is...

Which of the following chemicals contain pi bonds?

1. Nitrate, NO3-
2. Chloride, Cl-
3. Phosphate, PO4---
4. Calcium, Ca++
5. Ethanol, CH3CH2OH

Answers 2 (chloride) and 4 (calcium)are incorrect because they contain no bonds at all, and are just single atom ions.

Answer 5 is incorrect because ethanol contains all single covalent bonds, and all of those single bonds are called sigma bonds. A sigma bond involves sharing of electrons in the space directily between the two atoms involved, and it is that sharing of electrons that forms a strong covalent chemical bond.

Both nitrate and phosphate have one double bond between the central atom (N or P) and the oxygen atoms. They can be written as:

and

The double bond in each consists of one sigma bond like ethanol has, and one pi bond. pi bonds share electrons above and below the centerline between the atoms involved, like this (shown for a carbon-carbon double bond which has one sigma bond (red) and one pi bond (blue)):

As one added big complexity, all of the oxygen atoms in an isolated nitrate or phosphate ion are equivalent, and one cannot identify which oxygen has the double bonds. These are called resonance structures, kind of implying that the structure resonates between the different forms, but it's really just an average) and the ion acts as if the double bound is partly smeared out to each of the oxygen atoms:

 

[taricha]

So while we are on chemistry lectures that I slept through, what is a triple covalent bond called (like in N2), if a single covalent bond is sigma and a double bond is a pi?

 

[Randy Holmes-Farley]

So while we are on chemistry lectures that I slept through, what is a triple covalent bond called (like in N2), if a single covalent bond is sigma and a double bond is a pi?

lol

It has one sigma and two pi bonds.

One pi bond is above and below the atoms, and the other is to either side:

https://whatsinsight.org/wp-content/uploads/2021/05/hybridization-structure-diagram-of-n2-2-768x529.png

 

[taricha]

Thanks, Randy!
So I should be looking at that picture and imagine the bonds in 3 dimensions. Gross.

 

[Randy Holmes-Farley]

Thanks, Randy!
So I should be looking at that picture and imagine the bonds in 3 dimensions. Gross.

lol

yes, imagine the blue ones are pointing up and down, and the green ones in and out of the screen. The shapes try to indicate the areas most likely for the electrons to be, but of course they are trying to represent a probability of being in a 3D smear of likelihood with a simple line drawing.

the red sigma bond is mostly in the area between the N atoms.

The things that look like ones in the electron orbital drawings denote the electron spin, so are not really needed for this discussion