In this file is the description of molecular interactions, introduction, types of interactions, factors affecting them.

1. MOLECULAR INTERACTIONS IN
3D SPACE

2. Group Members
Maheen Imran (L1S21BSBT0106)
Sana Amir (L1S21BSBT0105)
Madiha Asad (L1S21BSBT0110)

3. MAHEEN IMRAN
(L1S21BSBT0106)
MOLECULAR INTERACTIONS IN
3D SPACE

4. Molecular Interactions:
“Molecular interaction are attractive and repulsive forces
between molecules and non bonded items.”

5. Importance Of Molecular Interactions:
• Protein Folding
• Drug Design
• Material Science
• Sensors
• Nano Technology
• Origin Of Life

6. Types Of Molecular Interactions:
• Intramolecular forces:
Intramolecular forces are the forces that hold atoms together within a
molecule.
i.e.;
chemical bonds such as ionic, covalent and metallic bonds.
• Intermolecular forces:
Intermolecular forces are forces that exist between molecules.
i.e.;
Dipole-dipole interactions occur in HCl molecules.

8. Difference In Intermolecular And Intramolecular
Intermolecular Force Intramolecular Force
• Intermolecular forces are the
forces that hold molecules in a
substance
• Intramolecular forces are the
forces hold atom in a molecule
• Weaker than intramolecular force • Stronger than intermolecular
force
• Determine the state and
properties of matter
• Determine the chemical behavior
of a substance
• Attractive forces • Chemical bonds

9. Categorization Of Forces:
Intermolecular forces are
categorized as:
• Ion dipole
• Dipole-dipole forces
• London dispersion
• Hydrogen bonding forces
Intramolecular forces are
categorized as :
• Covalent
• Ionic
• Metal bonds

10. Ion Dipole Forces:
“An ion-dipole interaction is the intermolecular force of attraction between a charge ion
(cation or anion) and a molecule.”
Found in solution where
ionic compounds dissolve in
polar solvents.

11. Example:
• Na+ (sodium ion) and H2O (water molecule)
• Na+: a cation
• Partially positive end of H2O: from H atoms
• Partially negative end of H2O: from O atom
Sodium attracts the oxygen atom of the water
molecule, while it repels the hydrogen atom.

12. SANA AMIR
(L1S21BSBT0105)
LONDON DISPERSION FORCES

13. London Dispersion Forces:
“Type of force acting between atoms and molecules that
are normally electrically symmetric.”
• It is the weakest intermolecular force
between non-polar molecules.
• Temporary attractive force makes it
temporary dipoles

16. Why Does The Temporary Dipole Occur?
• Results from random movement of electrons
• Induced dipole
• The net result is that there is a stronger
attractive force between molecules

17. Factors Affecting London Forces:
• Shape of the molecule
• Molecular weight
• Polarizability
• Distance between the molecules

18. Dipole-dipole Forces:
“Attractive forces between the positive end of one polar molecule and the negative end
of another polar molecule.”
• It is the electrostatic attraction between the molecules with permanent
dipoles.
• Cause an increase in Boiling point.
• For example,
The boiling point of HCl is 188K and that of F2 is 85 K

20. Factors Affecting Dipole-dipole Forces:
• Electronegativity difference
• Dipole moment
• Intermolecular distance

21. Strength Of Intermolecular Forces:

22. MADIHA ASAD
(L1S21BSBT0110)
HYDROGEN BONDING

23. Hydrogen bonding:
“Hydrogen bonding results from the attractive force between a hydrogen atom
covalently bonded to a very electronegative atom such as a N, O, or F atom
and another very electronegative atom.”
• Hydrogen bonding is a special type of dipole-dipole attraction between
molecules, not a covalent bond to a hydrogen atom.

25. Types of Hydrogen Bonding:
There are two types of H bonds, and it is classified as the following:
•Intermolecular Hydrogen Bonding
water and hydrogen fluoride
•Intramolecular Hydrogen Bonding
Salicilaldehyde and ortho – nitro phenol

26. Hydrogen bonding Strength:
• Hydrogen bond strengths range from 4 kJ to 50 kJ per mole of hydrogen
bonds.
• The strength of the hydrogen bond depends on the electronegativity of
the atoms H-F>H-O>H-N
• The hydrogen bond is a weak bond. The strength of hydrogen bond is
in-between the weak van der Waals forces and the strong covalent bonds.
• The dissociation energy of the hydrogen bond depends upon the
attraction of the shared pair of electrons and hence on the
electronegativity of the atom.

27. Conditions for Hydrogen bonding:
As a result of hydrogen bonding, a hydrogen atom links the
two electronegative atoms simultaneously, one by a covalent bond and the
other by a hydrogen bond. The conditions for hydrogen bonding are:
• The molecule must contain a highly electronegative atom linked to the
hydrogen atom. The higher the electronegativity more is the polarization
of the molecule.
• The size of the electronegative atom should be small. The smaller the
size, the greater is the electrostatic attraction.

28. Effects of Hydrogen Bonding on Elements:
• Association
The molecules of carboxylic acids exist as dimer because of the hydrogen
bonding (molecular masses double)
• Dissociation
In aqueous solution, HF dissociates and gives the difluoride ion instead of
fluoride ion. This is due to hydrogen bonding in HF.

29. Properties of Hydrogen Bonding:
• Solubility
• Melting and boiling point
• Volatility
• Viscosity and surface tension
• The lower density of ice than water

30. Hydrogen Bonding in Hydrogen fluoride:
Fluorine having the highest value of electronegativity forms the strongest
hydrogen bond.

31. Hydrogen Bonding in Water
A water molecule contains a highly electronegative oxygen atom linked to
the hydrogen atom.
Oxygen atom attracts the shared pair of electrons more and this end of the
molecule becomes negative whereas the hydrogen atoms become positive.

32. Hydrogen Bonding in Ammonia:
It contains highly electronegative atom nitrogen linked to hydrogen atoms.

33. Hydrogen Bonding in Alcohols and Carboxylic acid:
Alcohol is a type of an organic molecule which contains an -OH group.
Normally, if any molecule which contains the hydrogen atom is connected to
either oxygen or nitrogen directly, then hydrogen bonding is easily formed.

34. Hydrogen Bonding in Polymers:
Hydrogen bonding is an important factor in determining the 3D structures
and properties that are acquired by synthetic and natural proteins.
Hydrogen bonds also play an important role in defining the structure of
cellulose as well as derived polymers such as cotton or flax.

35. Hydrogen Bonding in Proteins:

36. Hydrogen Bonding in Nucleic Acid:

37. Video……
• https://www.youtube.com/watch?v=XEazos-Tdoo
• https://www.youtube.com/watch?v=q0cH8TUBHRU