Bond Polarity and Intermolecular Forces Flashcards
Define electronegativity
electronegativity is the ability of an atom to attract the bonding electrons towards itself in a covalent bond
What factors affect electronegativity
(CASh)
- Charge - more protons = stronger attraction between electrons and nucleus
- Atomic Radius - closer to nucleus = stronger attraction
- Shielding - less shells of electrons = less repulsion = stronger attraction
What is a non polar bond
when both atoms have the same electronegativity and so the bonding electrons are evenly distributed
What is a polar bond
when both atoms have different electronegativities and so a permanent dipole is formed
(permanent dipole = small difference in charge that results in a difference in electronegativities)
What are symmetrical and unsymmetrical molecules
symmetrical - they are non polar molecules due to the dipoles cancelling out
unsymmetrical - they are polar molecules due to the dipoles not cancelling out
What are intermolecular forces and what are examples of them
they are attractive forces between molecules that are only found in covalent structures:
- hydrogen bonds
- permanent dipole-dipole interactions (polar)
- induced dipole-dipole interactions (Van der Walls forces)
What are Van der Waals
they are very weak intermolecular forces that exist between all molecules
How is the strength of VDWs increased
strength increases as Mr increases due to the number of electrons increasing
straight chain alkanes have a higher boiling point than branches alkanes due to more points of contact
How strong are permanent dipole-dipole interactions
they are weak attractive forces between polar molecules
- they are stronger than VDWs
- they occur in addition to VDWs
- if a non polar molecule has a much greater Mr than a polar molecule, then the VDW can outweigh the PDD forces
Which has a higher boiling point Br2 or HBr
HBr contains a permanent dipole-dipole force between the polar molecules, whereas Br2 contains Van der Waals forces. Br2 has a higher Mr and so more electrons and therefore has stronger VDW forces and so has the higher boiling point
What are hydrogen bonds
it is a strong dipole-dipole attractions between molecules containing O-H, N-H, F-H bonds
it is exists between a H+ atom in one molecule and a lone pair on a highly electronegative atom (O-, N-, F-)
they are the strongest type of intermolecular force
What are the anomalous properties of water
- ice is less dense than liquid water due to an open lattice structure as the molecules are held further apart in ice
- water has a relatively high melting and boiling points due to the strong hydrogen bonds
