How Do Curly Arrows Illustrate Electron Movement in Acid Rain Formation?

[anabourdais]

Homework Statement

I have been working at this for about two days now and haven't really gotten any further. Unfortunately my teacher is away but last time he checked it over he said I was 'almost there' so a few extra nudges in the right direction would be appreciated!

I'm trying to write out the reaction mechanism for the formation of acid rain from atmospheric nitrogen. I know the general equations to go through but when it comes to showing the movement of electrons with 'curly arrows' I get stuck!

Homework Equations

1. O + N≡N → N=O + N

2. N + O=O → O + N=O

3. 2N=O + O=O → 2O=N=O

4. N=O + O=O=O → O=O + O=N=O

5. O=N=O + O-H → H=O=N=O
¦¦
O

The Attempt at a Solution

I know that electrons from the triple bond of the nitrogen in step 1 move to one N atom and this means that the O is attracted to the other N and they form NO.
I can also complete number 2 (i think) as it is the same as above, with different compounds. It's number 3 onwards that cause the problems.

any help appreciated!

 

[nate808]

Hello there,

First of all, great job on your attempts so far! It seems like you have a good understanding of the first two steps. Let me provide some guidance for the remaining steps:

Step 3: In this step, we have two NO molecules reacting with an oxygen molecule. The curly arrow should show the movement of a pair of electrons from the double bond of one NO molecule to the oxygen atom, forming a new double bond between the oxygen and that NO molecule. This will leave the other NO molecule with a single bond to the oxygen atom.

Step 4: Now, we have two NO2 molecules reacting with each other. Similar to step 3, the curly arrow should show the movement of a pair of electrons from the double bond of one NO2 molecule to the oxygen atom, forming a new double bond between the oxygen and that NO2 molecule. This will leave the other NO2 molecule with a single bond to the oxygen atom.

Step 5: This is the final step where we add water (H2O) to the reaction. The curly arrow should show the movement of a pair of electrons from the oxygen atom of water to the nitrogen atom of NO2, forming a new bond between them. This will result in the formation of HNO3 (nitric acid).

I hope this helps! Remember, the curly arrows always show the movement of a pair of electrons, and you should consider the electron pushing patterns and formal charges of the atoms involved in each step.

Best of luck with your assignment!

 

[Blueshift5]

I understand your struggle with writing out reaction mechanisms and using curly arrows. It can be a challenging skill to master, but with practice, you will get better at it.

First, let's start with the overall reaction for the formation of acid rain from atmospheric nitrogen:

N₂ + O₂ + H₂O → 2HNO₃

Now, let's break down the steps and use curly arrows to show the movement of electrons. Remember, curly arrows represent the movement of electron pairs, with the tail showing where the electrons are coming from and the head showing where they are going.

Step 1: N₂ + O₂ → 2NO
In this step, the double bond in N₂ breaks, and one of the electrons goes to one N atom, forming a lone pair. The other electron goes to the other N atom, forming a radical. The O₂ molecule also breaks, with one of the electrons going to the N radical, forming NO. The other electron from O₂ forms a lone pair on the other N atom.

Step 2: 2NO + O₂ → 2NO₂
In this step, the NO molecule reacts with another O₂ molecule. The N atom in NO donates a lone pair to O₂, forming an N-O bond and releasing NO₂. The other O atom in O₂ gains a lone pair, forming the second NO₂ molecule.

Step 3: 2NO₂ + H₂O → HNO₃ + HNO₂
In this step, one of the NO₂ molecules reacts with water. The N atom in NO₂ donates a lone pair to one of the H atoms in water, forming an N-H bond and releasing HNO₂. The other O atom in NO₂ gains a lone pair, forming HNO₃.

Step 4: HNO₃ + HNO₂ → 2HNO₃
In this final step, the HNO₃ molecule reacts with HNO₂. The N atom in HNO₃ donates a lone pair to the N atom in HNO₂, forming an N-N bond and releasing HNO₃. The other O atom in HNO₃ gains a lone pair, forming HNO₃.

Overall, the curly arrows show the movement of electrons from one atom to another, forming new bonds and breaking old ones. I hope this helps guide you in the right direction