4.4: INTERMOLECULAR FORCES

INTERMOLECULAR FORCES (IMF)

Intermolecular forces is one of the way for the molecules to communicate with its own molecules or with the other molecules. The interaction among the molecules will form either, Dipole - Dipole forces, Hydrogen Bond or Ionic Bond. 

OVERALL OF INTERMOLECULAR FORCES

In Chapter 4.2( Molecular Geometry & its polarity of the molecules), you have learned about determining the polarity of the molecules. Moreover, the polarity of the molecules will indicate the type of intermolecular forces of its molecules.

As the beginning of the topic INTERMOLECULAR FORCES, firstly, lets learn about VAN DER WAALS FORCES. 

There are 2 type of Van Der Waals Forces which are:-

1. London Dispersion Forces Or London Forces

2. Dipole - dipole Forces

LONDON DISPERSION FORCES

DEFINITION:

Force of attraction between instantaneous dipole that arise from a short time scale fluctuation in the electronic structure of species when they become very close to one another.

HOW DOES IT FORMS?

Diagram 1: Explanation for the Formation of London Dispersion Forces

All molecules whether it is polar or nonpolar or ions, they have London Dispersion forces when they interacts with their molecules or other molecules.

 ⇒⇒ Examples: H2 (molecules), ICl2 + (ion), CH3Cl (molecule) 

DIPOLE - DIPOLE FORCES (DD)

DEFINITION: Force of attraction between negative end of permanent dipole of one molecule and the positive end of permanent dipole of another molecule.

HOW DOES IT FORMS?

Diagram 2: Explanation for the Formation of Dipole-dipole Forces

     

Diagram 3: Example of molecules of greater polarity of molecules with greater dipole-dipole forces

*** KEYPOINTS: Type of IMF for

1) Polar molecules - London dispersion forces & Dipole - dipole Forces

2) Nonpolar molecules - London dispersion forces  

 FACTORS THAT AFFECTING THE STRENGTH OF VAN DER WAALS FORCES

Chart 1: Summary of Factors Affecting The Strength of VDW Forces

This is just brief explanation of the factors Affecting The Strength of VDW Forces. Refer to the lecture notes on this part for some example & explanation of the topic.

HYDROGEN BOND (HB)

DEFINITION: Attractive forces between the positively charged H atom of a polar molecule and the negatively charged electronegative atom (F, O, N) of another molecule

*The interaction is between H from one polar molecules (H is must directly bonded to F or O or N in its molecules) with F,O,N from the other polar molecules

EXAMPLES:

Diagram 4: Interaction between 2 molecules in order to form Hydrogen Bond

*** Hydrogen Bond is weaker IMF than Ionic Bond 

*** But, Hydrogen Bond is stronger IMF than London dispersion forces & Dipole - dipole forces

Effect of Hydrogen bonding on physical properties

Chart 2: Summary about the effect of Hydrogen Bond in the molecules

Diagram 5: Differences between structure in ICE (SOLID) & WATER (LIQUID)

EXAMPLE OF IMF AMONG MOLECULES

1. HF molecules

    - is POLAR MOLECULES

    - contains of Hydrogen bond, Dipole - dipole forces & London dispersion forces              between its molecules

    - the MOST DOMINANT IMF in HF molecules is HYDROGEN BOND

2. HBr molecules

    - is POLAR MOLECULES

    - contains of Dipole - dipole forces & London dispersion forces between its                      molecules

    - the MOST DOMINANT IMF in HBr molecules is DIPOLE - DIPOLE FORCES

3. CH4 molecules

    - is NONPOLAR MOLECULES

    - contains of London dispersion forces between its molecules

    - the MOST DOMINANT IMF in CH4 molecules is LONDON DISPERSION FORCES

4. SF6 molecules

    - is NONPOLAR MOLECULES

    - contains of London dispersion forces between its molecules

    - the MOST DOMINANT IMF in SF6 molecules is LONDON DISPERSION FORCES

5. Interaction between H2O with CH4

    - H2O is POLAR MOLECULES 

    - contains of Hydrogen bond, Dipole - dipole forces & London dispersion forces between its molecules   

     

    - CH4 is NONPOLAR MOLECULES

    - contains of London dispersion forces between its molecules

  

    -Thus, the interaction between both molecules is LONDON DISPERSION FORCES

* Do exercises on IMF (LECTURE NOTES). 

* Please write some comment on this post as I know you have read my blog on this topic. TQ😍

GOOGLE FORM 4.4

All of my students must answer this form before SUNDAY (1/11/2020, 6PM). Upon your response is taken has attendance of tutorial. tq