LDF Bond Strength

[Leyla Anwar 3B]

One of the sapling question asks us to list the order from strongest to weakest LDF bond. The molecules were I2, Br2, and Cl2 and placed in that order. The reasoning was that the larger and heavier the atom, the stronger the bond length. I thought it would be the opposite because the larger the atom the longer the bond and therefore the weaker the bond. Could someone please explain?

[Luveia Pangilinan 1A]

I'm not quite sure. From my own understanding, I also thought they were inversely related. The shorter the bond length the stronger it is and vice versa.

[reyvalui_3g]

In the case of London Dispersion Forces, what determines there bond strength is how often two atoms will bond at their instantaneous dipoles.

In larger atoms, the attractive force on their valence electrons is less than that of smaller atoms due to electron shielding. This means that these valence electrons, which are travelling around the nucleus in a wavelike manner, are more likely to form an instantaneous dipole that will disrupt the electron cloud a neighboring atom.

This means that the more often instantaneous dipoles are created between two atoms, the longer they stay bonded, which increase the LDF.

[Sreeram Kurada 3H]

The larger the atom the more chance individual electrons could interact with each other. As a result, the LDF forces between these electrons is greater.

[anikamenon2H]

Larger molecules have more electrons that are farther away and thus, less tightly held. Because of this, there are more easily distorted and thus, there is more possibility for them to interact with the other valence electrons of the other atom and form temporary dipoles, making the dispersion force stronger as the molecule gets larger/heavier.

Hope this helps!

[Benjamin Chen 1H]

Just to add to this, LDF is an intermolecular force meaning it's between other molecules, so the r^6 refers to the distance between two molecules and not the bond length. When considering the strength of the Intermolecular Forces, the bond strength or bond length shouldn't be a big factor for LDF, rather you would consider the polarizability of the molecule.

This would mean the "size" of the molecule in terms of how many electrons there are.

[Faith Lee 2L]

Adding onto what Ben said, I think you might be thinking of intramolecular forces, where the bond strength/length really would matter. However, LDF occurs between molecules, not within them, making them an intermolecular force. In this case, a greater number of electrons would allow for greater attraction :) Hope this helps!

[Sreeram Kurada 3H]

The bigger the atoms the greater the chance the electrons of the atoms have in interacting with each other, which as a result leads to stronger LDF forces.

[Binyu You]

I believe the larger the atom(lower and to the right of periodic table, the stronger the LDF forces.

[Scot Widjaja Dis 1J]

The larger the atom, the more easily the electrons in the cloud can get distorted, and this leads to stronger London dispersion forces between the atoms. Since I2 is bigger than Br2, which is bigger than Cl2, I2 has the ability to form stronger attractive forces with other molecules.

[Eliana Witham 2H]

The more electrons there are, the more electron shielding there is. Therefore, another molecule will more easily distort (or pull) the electrons in the large molecule, creating greater LDF's.

[Gabriel Nitro 1E]

Hi,

The reason the list of LDFs are listed as it is, is because the size of I2 is far larger than that of the other diatomic molecules with the most number of electrons. This results in a greater polarizability and in turn, leads to stronger LDFs.

Hope this helps! :)