Double Bonds

[Juwan_Madaki_3K]

When drawing a Lewis structure like COCl2, how do you decide if the CL or O gets the double bond? Is it usually the element with the higher ionization energy?

[Praneetha Kakarla 3A]

Hey! You would look at the formal charges to see where the double bond should go. You want the formal charges to be as close to 0 as possible.

For COCl2, if you put the double bond b/w C & Cl, the Cl atom will have a formal charge of +1 & the O atom will have a formal charge of -1.
If you put the double bond b/w C & O, all the atoms' formal charges will be 0. Therefore, this is the preferred (most stable) structure.

[Akriti Ratti 1H]

Hi!, you'd want to form a double bond that minimizes the formal charge.

[OwenSumter_2F]

Like others said, find the one with the least formal charge, but if resonance is in question, you'll want both types with an arrow pointing between the two.

[Bella Bursulaya 3G]

Look to see which one would have the lowest formal charge, but also it would make sense for the higher ionization element/more electronegative element to get the partial negative charge if you couldn't form a double bond. Also you need to make sure that Cl wouldn't have a + charge, because Cl is very electronegative and doesn't want to share electrons.

[Katie Le 3K]

You'd look to see if the formal charge of the molecule would be 0 because it's more stable/more likely to happen.

[jessicasilverstein1F]

You would want to place the double bond wherever it makes the formal charges closest to zero

[aashmi_agrawal_3d]

You would place the double bond where it would result in the lowest formal charges.

[apurva-3E]

Where the least formal charge is!

[EmilyGillen_1A]

Like everyone said, you want to take into account how the double bond will affect formal charge (if it will bring the charge lower/closer to 0, or if it will increase the formal charge). But I also wanted to mention that my TA was talking about this and for Cl there will never be a double bond (I am sure there are some weird exceptions, but from what she said we will never be double bonding Cl). She went through and explained why, but the jist is that Cl is so electronegative and needs 1 electron, that to double bond it would be extremely unfavorable and unstable- it would make the formal charge 1 which would not be a stable state for Cl to exist.
-So for cases like this you can also remember that Cl will not have a double bond, so it has to go to Carbon.

[Chelsea_Guzman_3C]

To further emphasize what the previous person said, Cl never has a double bond because it is just not stable enough to have that. Oxygen is most likely to carry this, so that it a helpful tip to know! But it would usually go to the element with the least formal charge.

[SamanthaTolentino 3D]

The formal charge is typically what we look at to determine which gets the double bond. We want a more stable atom so we want most of the molecules to have a 0 formal charge which is most favorable/stable.