Different Types of Intermolecular forces

What is intermolecular force ?

Is a type of forces that hold molecules together, ie : between molecules

The further away from the nucleus the intermolecular force are stronger

What are the 3 types of intermolecular forces ?

• Van Der Waals ( weakest IM force )

• Permanent dipole - permanent dipole

• Hydrogen Bonding ( Strongest IM force )

What are the types of forces between ionic / covalent bonding ?

Ionic compound / molecules attract through electrostatic force of attraction

Covalent bonding / simple molecular … attract through the 3 types of IM forces

Van Der Waals

• weakest bond held between molecules/ last the shortest —> exist between all molecules

• No of electrons increased → VDW forces get stringer —> increase the boiling points —→ more eggy needed to overcome the VDW forces

• electrons are moved quickly —> likely to move from one to another to create a temporal dipole —. Causes another temporary dipole in the opposite direction. —» Causes a 3rd temporary dipole.

→ Causes an effect of atom / molecule to be attracted to another

• If the molecule are branched → VDW forces get weaker as there’s smaller contact space for the IM forces

Permanent Dipole - Permanent Dipole

Permanent intermolecular force between 2 dipoles

Theses are in addition to VDW forces

Permanent dipole - induced dipole

• need 2 molecules, each with a polar bond. ( 2 elects with a large enough difference in electronegativity)

• Stronger than VDW forces / Weaker then PD - PD

Hydrogen Bonding

HF / H2O / NH3 —> always have a hydrogen bond

How do we know if it is hydrogen bonds ?

When the hydrogen reacts with nitrogen, oxygen or fluorine

Why is hydrogen bond the strongest

strong electrostatic attraction between a hydrogen atom bonded to a highly electronegative atom (like O, N, or F) and the partial negative charge on another electronegative atom. 

Why does iodine have a higher melting point than fluorine?

Cuz as u go down the group the nuclear charge increase , more electrons, stronger VDE forces holding the electrons together