Dr Bob

Although helium atoms do not combine to form He2 molecules. is it true to say that He atoms are weakly attracted to one another from London dispersion forces (induced dipole forces) or is there another force at play?
It cant be Hydrogen bonding(there is no hydrogen here)
it cant be dipole induced dipole forces or ion-dipole forces or even dipole-dipole forces can it ??
Can you clarify for me please
Thanks
Andy

Actually, He does form diatomic bonds, and He2 forms in the milliKelvin range. The very weak Van der Waals forces are responsible. At normal temperatures, these forces are so small as to be responsible for the very weak attraction seen. No hydrogen, nor dipole forces are present.

thanks andy

Hi Andy! You're correct that helium atoms do not form He2 molecules. However, they do experience weak attractions to one another through a force called London dispersion forces, also known as induced dipole forces.

London dispersion forces occur between all atoms and molecules, including noble gases like helium. These forces arise due to temporary fluctuations in electron density, resulting in the temporary creation of an instantaneous dipole moment. This dipole moment induces a neighboring atom or molecule to similarly develop a temporary dipole. These temporary dipoles then attract each other, leading to weak intermolecular forces.

Other forces you mentioned, such as hydrogen bonding, dipole-induced dipole forces, ion-dipole forces, or dipole-dipole forces, are not applicable to helium because they require the presence of specific types of atoms or molecules.

In summary, helium atoms are weakly attracted to one another through London dispersion forces or induced dipole forces. These forces are due to temporary fluctuations in electron density and occur among all atoms and molecules.

Hello Andy,

You're correct that helium atoms do not form He2 molecules because helium is a noble gas, which means it already has a full outer shell of electrons and is therefore very stable. However, there are indeed weak attractions between helium atoms due to what are known as London dispersion forces or induced dipole forces.

London dispersion forces are temporary attractive forces that occur between all molecules or atoms. These forces arise due to the motion of electrons within the atoms or molecules. At any given moment, there may be an uneven distribution of electrons, creating a temporary dipole in one atom or molecule. This temporary dipole can induce a dipole in a nearby atom or molecule, leading to a weak attraction between them.

Although helium atoms don't have a permanent dipole moment (because they have a symmetrical electron distribution), the motion of electrons can still result in temporary dipoles. As a result, helium atoms can experience induced dipole-induced dipole (London dispersion) forces. These forces are generally quite weak compared to other types of intermolecular forces, but they are still present.

On the other hand, you correctly pointed out that hydrogen bonding, dipole-induced dipole forces, ion-dipole forces, and dipole-dipole forces are not at play here. Hydrogen bonding requires hydrogen directly bonded to elements such as nitrogen, oxygen, or fluorine, which is not the case in helium. Dipole-induced dipole forces and ion-dipole forces occur between polar molecules or ions, which helium atoms are not. Similarly, dipole-dipole forces require polar molecules, whereas helium is a nonpolar atom.

In summary, the weak attractions between helium atoms are primarily due to London dispersion forces or induced dipole forces. These forces are the result of temporary fluctuations in electron distribution, even though helium atoms don't possess a permanent dipole moment.

I hope this clarifies things for you! Let me know if you have any further questions.