Van der Waals forces Flashcards
3 Types of Van der Walls force
London dispersion forces
Permanent dipole - permanent dipole
Hydrogen bonding
Description of London dispersion forces
London dispersion forces are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles due to the uneven distribution of electrons in atoms and molecules.
Effect of atom size on London dispersion forces
Larger atoms have more electrons,
Allows for greater uneven distribution of these electrons
Creating stronger temporary dipoles
Meaning greater attractions between the atoms
What structures experience London dispersion forces
All atoms and molecules however they are only significant for atoms and molecules that experience no other types of attractions
How strong are London dispersion forces?
They are weak
How do permanent dipole - permanent dipole interactions arise
They are the electrostatic forces of attraction between the slightly positive end of one polar molecule and slightly negative end of another polar molecule.
What structures experience permanent dipole-permanent dipole interactions
Polar molecules
How strong are permanent dipole - permanent dipole interactions
Strong
For hydrogen bonding to occur the hydrogen atom involved must be
The positive end of a strong dipole, have a small, highly electronegative atom on a neighbouring molecule
What are the only atoms that can result in hydrogen bonding is a hydrogen is bonded directly onto them
Fluorine, Nitrogen and oxygen
How does hydrogen bonding arise
They are the electrostatic forces of attraction between molecules that contain hydrogen atoms bonded to small, highly electronegative atoms. This means that the the hydrogen will effectively lose its outer electron meaning it’ll have a very positive dipole allowing it to have incredibly strong forces of attraction between molecules
How strong is hydrogen bonding
Very strong - strongest of the three forces
Why does ice float in water
The intermolecular bonds are now rigid meaning that air will be trapped inside of them causing the ice to have a lower density than the water so therefore it will float in water as it won’t have any air trapped between the bonds.
The hydrogen in ice results in an expanded structure.
Viscosity
The stronger the intermolecular bonding is, the more viscous the substance will be
Solubility -
Like dissolves like
For example a polar molecule will be absorbed in a polar liquid like water for example - like dissolves like
