6.3 : Intermolecular Forces Flashcards
What are the three different types of intermolecular forces?
Induced dipole - dipole interactions ( London forces )
Permanent dipole - dipole interactions
Hydrogen bonding
Define intermolecular forces
Weak interactions between dipoles of different molecules
Order the intermolecular forces from strongest to weakest
( covalent )
Hydrogen bonds
Permanent dipole dipole
London forces
Describe how induced dipole - dipole interactions occur
Movement of electrons produces a changing dipole in a molecule
At any instant, an instantaneous dipole will exist, but it’s position is constantly shifting
The instantaneous dipole induces a dipole on a neighbouring molecule
The induced dipole induces further dipoles on neighbouring molecules, which then attract one another.
What is another name for induced dipole - dipole interactions ?
London forces
Are London forces permanent or temporary?
Temporary
How do you increase the strength of London forces?
The more electrons in each molecules
The larger the instantaneous and induced dipoles
The greater the induced dipole - dipole interactions
The stronger the attractive forces between molecules
What are permanent dipole dipole interactions ?
They act between the permanent dipoles in different polar molecules.
How does have permanent dipole dipole interactions affect boiling point? Give an example with fluorine and HCl
F = non polar, only London forces HCL = polar, have London forces and permanent dipole dipole interactions
Extra energy required to break the additional permanent dipole dipole interactions
Boiling point of HCL is higher than F2
What a simple molecular lattice?
The molecules are held in place by weak intermolecular forces
The atoms within each molecule are bonded together strongly by covalent bonds
They are formed from simple molecules
Describe and explain the boiling and melting points of simple molecular substances
The weak intermolecular forces of a simple molecular lattice can be broken even by the energy present at low temperatures.
Therefore, they have low melting and boiling points.
What happens when a simple molecular substance is melted?
Only the weak intermolecular forces break
The covalent bonds are strong and do not break
Describe and explain the solubility of non - polar simple molecular substances
When it is added to a non polar solvent, imf’s form between the molecules and solvent.
The interactions weaken the imfs in the simple molecular lattice. The imfs break and the compound dissolves.
When it is added to a polar solvent, there is little interaction between the molecules in the lattice and the solvent molecules.
The intermolecular bonding within the polar solvent is too strong to be broken.
Summarise the solubility of non polar simple molecular substances
Not soluble in polar solvents
Soluble in non polar solvents
Describe and explain the solubility of polar simple molecular substances
They may dissolve in polar solvents as the polar solute molecules and the polar solvent molecules can attach each other.
The solubility depends on the strength of the dipole and can be hard to predict.
