7A Intermolecular Forces - Edexcel IAS Chemistry (Unit 2)

[@rafiatbm7867]

2 QUESTIONS about Hydrogen bonds.. We know that oxygen atoms in water have two lone pairs thus that central electronegative oxygen atom in water can form two hydrogen bonds with two other distinct water molecules (15:30) and simultaneously we also know that water contains two electropositive hydrogen atoms so thus it can form two hydrogen bonds per molecule (that's what my 2nd Ques points)….. Now here's the thing, fluorine also has 3 lone pairs because it forms a covalent bond with a hydrogen atom with just one unpaired electron it has and it has its 3 lone pairs of electrons... I have two questions here… Q1: Can I say that the central electronegative fluorine atom of Hydrogen fluoride can form three more hydrogen bonds with other 3 individual electropositive hydrogen atoms of other three distinct respective HF molecules? Q2: I know for a fact that hydrogen fluorides have only just one hydrogen bond per molecule since it has only one electropositive hydrogen atom… So does that mean that in general the number of hydrogen bonds that a molecule can form depends on the number of electropositive hydrogen atoms that molecule has and not how many hydrogen bonds the central electronegative atom can form with other equivalent number of molecules ??

[@MissNatalieChemistry]

Yes you are quite right that each lone pair in on the fluorine can form hydrogen bonds with the H atom on another molecule of HF, however unreality they do not as there would not be enough H atoms for each F to form 3 hydrogen bonds. Therefore the number of hydrogen bonds formed is generally not to do with how many lone pairs are on each atom but simply how many electropositive atoms are available to make the hydrogen bond.

[@BuilderLemon]

Thank you for making this video. I just have a question about the "hydrogen bonds are directional in nature" part: what do you mean by directional? And how is hydrogen bonding directional?

[@MissNatalieChemistry]

Directional bonding means that the atoms prefer to be in a specific orientation relative to each other. So for hydrogen bonding the atoms are attracted to each other in a specific way which holds them in a linear arrangement to each other so the bond angle is 180

[@amorqwerty]

where can i print out these presentations

[@pakpumet.6728]

Thankyou!

[@diexzz7074]

In the pastpaper q why is the C-H bond is rejected as permeant dipoles, dont the have different electronegativity ??, and other compounds such as sih4 geh4 snh4 are said to have only london forces but not permanent dipoles interaction. im confused

[@MissNatalieChemistry]

C-H bond does not have a big enough difference in electronegativity to form a permanent dipole. The difference in electronegativity is only 0.3 and it should be generally above 0.5 for a permanent dipole.

[@diexzz7074]

@@MissNatalieChemistry thank you

[@rafiatbm7867]

2 QUESTIONS about London forces.. Q:1 Can you elaborate up a little bit more about the the London forces in molecules?? Is the electron clouds of of the two atoms forming covalent bonds between each other gonna superpose and electrons will be able to freely move along the entirety of it?? If that's so, can you explain up a little bit more about this kind of effect as I'm not being able to wrap around my head regarding this... Q2: Does the asymmetry in oscillation of electrons within their orbital occurs just like that , Oooorrr is it because in covalent molecules the bond pair of electrons tend to oscillate from the mean central position within the bonded atoms?? Suppose Br2 molecule is Br(1)--Br(2).. What I think is happening is that due to the oscillation of their bond pair of electrons, at one instant the bond electron pair oscillates and go towards Br(2) which makes the Br(2) electronegative and Br(1) electropositive... And this happens because the orbital electrons of Br(2) got shifted towards the other side(i.e. its right side) due to the electrostatic repulsion between the Br(2)'s orbital electrons and the bond pair of electrons and thus the electron density got increased there..Is this what happens?? (This is what I wanted to ask in Q2)... Then I'm confused at exactly what way the polarisation took place...Does it form superposed electron cloud like that and all the overall electrons (70 electrons) oscillate within the entire superposed atomic orbitals , and overall one side have more electrons, making it delta- and vice versa happening to the other side ?? (This is what I wanted to ask in Q1)..

[@MissNatalieChemistry]

Firstly, no the electrons in a covalent bond do not travel throughout the entire molecule. They remain attracted to their own individual nucleus but the shared pair of electrons holds the two atoms together in the molecule. London forces are formed by asymmetrical movement of electrons in a molecule (as of course electrons are always moving around in their individual atom) which causes an instantaneous dipole which is in turn causes an induced dipole in a neighbouring molecule. These short lived dipoles are attracted to each other and this keeps the molecules together (intermolecular forces).

[@movielife1425]

You said that instantaneous dipole only last for short period ,soo does it go back to the symmetrical movement ?

[@MissNatalieChemistry]

Yes it will go back to a symmetrical movement but will then become unsymmetrical again. It is a cycle of symmetrical and unsymmetrical movement meaning that the dipole cycles through existing and not existing. However this is a very fast process so dipoles will always exist somewhere in the molecule at any given time causing the forces of attraction.

[@dude_mude3366]

THANK U U U U U U

[@BLACKWHITE-og3rg]

thab=nk u miss