Question

Please give your own examples of intermolecular forces: The forces that hold condensed states together. Below you will find key questions.

1. Know and understand the phenomenon of hydrogen bonding.

6. Predict the ability of molecules to exhibit hydrogen bonding.

7. Recognize hydrogen bonding as the force that holds double-stranded DNA together.

8. Rank a series of molecular compounds with respect to the boiling point.

9. Know and understand that the interaction of ions and dipoles leads to the dissolution and solvation of ions by water and other polar liquids.

Answer 1

Intermolecular forces are attractive interaction between positive and negative ends of different molecules.

There are 4 types of intermolecular forces

a. Coulombic forces: forces between two ions, these are ionic forces. e.g. NaCl

b. Dipole forces: forces between the two dipoles i.e. between two partial charged ends or in polar covalent molecules e.g. HCl

c. Dipole-Dipole interaction: forces between plar molecules, when positive end of one molecule is attracted by negative end of other polar molecule. e.g. SO2

d. Ion-Dipole interaction: Forces between an ion and polar molecules. e.g. Na+/water cluster.

Answers:

1. Hydrogen Bonding: It's a special case of dipole forces. When a hydrogen atom attach to an electrnegative atom i.e. N, O, F due to electronegativity difference between H and X( X= N, O, F) X pulls electron density towards it. Since electron density is more at X so it becomes partially negative and H become partially positive due to this X(of one molecule)attracted towards the partially positive H of other molecule and partially positive H(of first mollecule) is attracted by partially negative X of other molecule. This type of interaction is called H-bonding.

6. Ability of molecule to shoe H-bonding: Molecules in which H atom undergoes for dipole-dipole attraction to an electronegative atom specifically N, O, F which withdraws electron density from H atom and becomes electron rich and makes H atom electron deficient due to which dipoles appear in molecule and both H atom(electron deficient) and X(X=N, O,F electron rich) attracted to opposite poles of other molecule and a bond between partially positive H atom and partially negative x is formed this is the H bond. H bond is not a covalent bond since it is only attraction between partial opposite poles. i.e. dipole-dipole attraction.

7. H-bonding in double stranded DNA: In double stranded DNA both two strands are cmplementary to each other. both contains base pairs purin and pyrimidine. Since base contains N atom (essential in our body as protien) so this N attract towards the H present in the other base. Purin bases are Addinine and Guanine and pyrimidine bases are Cytocine, Thymine and Uracil. In DNA Addinine of purin form H-bonding with Thymine of pyrimidine and Guanine of purin for H-bond with Cytocine of pyrimidine( there is no Uracil in DNA, it is in RNA). So Cyt. form 3 H-bond with Guan. and Thy. form 2 H-bond with Addin. which binds both the strand strongly in DNA double strand.

8. Molecular compounds with respect to boiling point: Since H-bonding is the stronger than dipole dipole and van der Waals attraction hence molecules having H-bonding will have highest boiling point.

Strength of attraction: H-bonding>dipole-dipole>Van der Waals

Boiling point: H-bonding>dipole-dipole>Van der Waals

below is the series-----

9. Interaction of dipole and iond leading dissolution and solvation: Dissolution means the process of dissolving or forming a solution. When dissolution happens, the solute separates into ionsor molecules and each ion is surrounded by the oppositely charged ends of solvent molecules. The interaction between solute particle and solvent molecules is called solvation.

e.g. when NaCl dissolve in H2O it breaks into ions Na+ and Cl- each of ion is surrounded by the water molecules i.e. Na+ surrounded by O end of H2O(negative ends) and Cl- is surrounded by H end(positive ends) and both the ions separated and the process of solvation completed.

Hope it will help!