Help with molecular structure and dipole please.

[JohnDoeDDS]

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Ok guys, I am studying for my final, but the professor also gave us an online quiz to be counted as extra points. The problem is I cant really find this anywhere and am having great trouble drawing this structure. Truth is if this was to show up on the ifnal I would be screwed. Can you guys PLEASEEE help me out with this. Maybe some1 has a link to this online. Ive searched google but have had no luck. Ok here is the question:

Molecule PCl2F3 forms three isomers. Two of these Isomers have a dipole. Construct the model for each isomer and idicate which ones have a dipole.

I am having trouble determining which one is the central atom along with how to draw the molecule in three different ways. I would really appreciate it if someone could help me out. Thanks in advance.

 

[JerseyGirl83]

you can make that central.. again, i may be wrong as I havent looked at this stuff for years!!

 

[cameltoe]

Ok guys, I am studying for my final, but the professor also gave us an online quiz to be counted as extra points. The problem is I cant really find this anywhere and am having great trouble drawing this structure. Truth is if this was to show up on the ifnal I would be screwed. Can you guys PLEASEEE help me out with this. Maybe some1 has a link to this online. Ive searched google but have had no luck. Ok here is the question:

Molecule PCl2F3 forms three isomers. Two of these Isomers have a dipole. Construct the model for each isomer and idicate which ones have a dipole.

I am having trouble determining which one is the central atom along with how to draw the molecule in three different ways. I would really appreciate it if someone could help me out. Thanks in advance.

1) P is the central atom...one with 5 bonds (2 Cl single bonds and 3 F single bonds)

2) one with 6 bonds (1 Cl single bond, 1 Cl double bond, and 3 F single bonds)

3) one with six bonds (2Cl single bonds, 2F single bonds, and 1 F double bond)

2 and 3 have dipole moments

 

[dinesh]

How does phospherus end up with a valency of +6 cameltoe

It's a trigonal bipyarmidal strucutre, T shaped, so I was thinking more along the lines of arranement to givve something "sorta symmetrical" to give no dipoles ,and the other 2 giving it.

 

[cameltoe]

I also wanted to add this because I think its important to know (not just for chemistry, but for the DAT or the MCAT (if you decide to take it)

the reason P is able to have so many electrons in its outer shell is because it contains a D orbital. Compounds like Carbon and Nitrogen only contain S and P orbitals and hence are able to carry no more than 8.

 

[cameltoe]

How does phospherus end up with a valency of +6 cameltoe

It's a trigonal bipyarmidal strucutre, T shaped, so I was thinking more along the lines of arranement to givve something "sorta symmetrical" to give no dipoles ,and the other 2 giving it.

1)The charge of P will be for the first one = neutral
2) for the second one = (-1) 5-6
3) for the 3rd one = (-1) 5-6

the reason it is able to have 6 bonds is because it contains a d orbital

 

[gatszu]

the halogens do not form double bonds. the corect structure would be P in the center, Cl & F around it. no dipole when you have the Cl 180 degrees apart (at the apeces) & the F on the equator 120 degrees apart. you can also have two of the Cl on the equator, or one Cl on the equator & one at an apex. there are a total of 40 valence electrons, 8 on each halogen & 10 on P (=5 bonds).

1) P is the central atom...one with 5 bonds (2 Cl single bonds and 3 F single bonds)

2) one with 6 bonds (1 Cl single bond, 1 Cl double bond, and 3 F single bonds)

3) one with six bonds (2Cl single bonds, 2F single bonds, and 1 F double bond)

2 and 3 have dipole moments

 

[gatszu]

I also wanted to add this because I think its important to know (not just for chemistry, but for the DAT or the MCAT (if you decide to take it)

the reason P is able to have so many electrons in its outer shell is because it contains a D orbital. Compounds like Carbon and Nitrogen only contain S and P orbitals and hence are able to carry no more than 8.

not only C & N, but that whole row do not have expanded octet due to lack of d orbitals, F included! Hence, no F does not form double bond.

 

[gatszu]

1)The charge of P will be for the first one = neutral
2) for the second one = (-1) 5-6
3) for the 3rd one = (-1) 5-6

the reason it is able to have 6 bonds is because it contains a d orbital

in generating stable stuctures, you must minimize separation of charges. a double bond would give P a -1 & F or Cl a +1. F & Cl are never +1. they are highly electronegative, F = 4 & Cl =3 on the electronegativity scale (& 4 is the highest). therefore, 2 & 3 are incorrect.

 

[cameltoe]

in generating stable stuctures, you must minimize separation of charges. a double bond would give P a -1 & F or Cl a +1. F & Cl are never +1. they are highly electronegative, F = 4 & Cl =3 on the electronegativity scale (& 4 is the highest). therefore, 2 & 3 are incorrect.

I stand corrected 😀

 

[gatszu]

😀

 

[AUG2UAG]

the halogens do not form double bonds. the corect structure would be P in the center, Cl & F around it. no dipole when you have the Cl 180 degrees apart (at the apeces) & the F on the equator 120 degrees apart. you can also have two of the Cl on the equator, or one Cl on the equator & one at an apex. there are a total of 40 valence electrons, 8 on each halogen & 10 on P (=5 bonds).

yes! 👍

trigonal bipyramidal sp3d

 

[JohnDoeDDS]

okay I am completely confused now thanks guys. lol j/k....
I understand that elemsnts in periods 1 and 2 cant have an expanded octet because no d shell. That part I get. (What did u mean in terms of DAT how would they as something like this on DAT? Just curious). Anyway Im still dumbfoudned as to the answer to the question.

The only one I understand is where you have the 2 Cls on on top on on the bottom, and then have the Fs on the equator. That would give me no dipole. But Im having trouble seeing the other variations.

 

[gatszu]

the halogens do not form double bonds. the corect structure would be P in the center, Cl & F around it. no dipole when you have the Cl 180 degrees apart (at the apeces) & the F on the equator 120 degrees apart. you can also have two of the Cl on the equator, or one Cl on the equator & one at an apex. there are a total of 40 valence electrons, 8 on each halogen & 10 on P (=5 bonds).

in bold are the two other structures. both have dipole moments. draw them out & you will see.

 

[JohnDoeDDS]

thanks guys I just sat there and drew them out and finally got it. Had the final yesterday and this wasn't on it although a bunch of other structures were I think I got them right though.. Final was hard as ****. One concept question I couldnt get was why is Nitrogen bigger then Fluorine?!!!! I though Flourine is bigger since it has more electrons hence more e-e repulsion. Why am I wrong?

 

[Utes]

For your last question about which one is bigger...

This is covered in the Kaplan book in Gen Chem Ch 2 - Periodic Table. The trend of atomic radius is such that it increases as you go down the group and to the left on the period. F is going to be small, then as you go left to get to Nitrogen, the trend is that the atomic radius will get bigger.

They say: "As one moves from left to right across a period, electrons are added one at a time to the outer energy shell. Electrons within a shell cannot shield one another from the attractive pull of protons. Therefore, since the number of protons is increasing, producing a greater positive charge attracting the valence electrons, the effective nuclear charge increases steadily across a period. This causes the atomic radius to decrease."

For more see page 204 of the Kaplan DAT book 3rd edition.

 

[JohnDoeDDS]

I seee. I didnt realize about the protons. Oh well now if I get this question on the DAT Im def. going to get this right! Thanks for the explanation.