Importance of Intermolecular and Intramolecular Forces of Attraction

IMPORTANCE OF INTERMOLECULAR FORCES OF ATTRACTION

                                       Intermolecular forces of attraction exist between the molecules and although they are much weaker that the intramolecular forces of attraction, they still have a significant role to play. Because they help in determining the physical properties of molecules like:

•       The boiling point
• ·          Melting point
• ·         Density
• ·         Enthalpies of fusion and vaporization

              The intermolecular forces of attraction are also the reason behind why the molecules in liquids and solids stick around each other. Boiling and melting points of compounds depend on the type and strength of the intermolecular forces present as tabulated below:

Type of Compound	Intermolecular Forces of Attraction present	Relative order of boiling and melting points
Ionic Compounds	Ion to ion attraction between ions, London dispersion forces	1 (highest)
Covalent Compounds containing hydrogen bonds	Hydrogen bonds, London dispersion forces	2
Polar Covalent Compounds	Dipole-dipole attraction between dipoles created by partially charged ions, London dispersion forces	3
Non-polar Covalent Compounds	London dispersion forces	4 (lowest)

RELATIVE STRENGTH OF INTERMOLECULAR FORCES OF ATTRACTION

Intermolecular Force	Occurs between...	Relative Strength
Dipole-dipole attraction	Partially oppositely charged ions	Strongest
Hydrogen Bonding	H atom and O, N or F  atom	As strong as the dipole-dipole attraction
London Dispersion Attraction	Temporary or induced dipoles	Weakest

IMPORTANCE OF INTRAMOLECULAR FORCES OF ATTRACTION

                                          From the given meaning of the intramolecular forces of attraction, the importance of it is it basically holds atoms together and keeping it intact with each other so it won’t be easily destroyed.

RELATIVE STRENGTH OF THE INTRAMOLECULAR FORCES OF

ATTRACTION

Intramolecular Force	Basis of Formation	Relative Strength
Metallic Bond	Metal cations to delocalized electrons	1 (strongest)
Ionic Bond	Cations to anions	2
Polar Covalent Bond	Partially charged cation to partially charged anion	3
Non-polar Covalent Bond	Nuclei to shared electrons	4 (weakest)

PRACTICAL EXAMPLES OF INTRAMOLECULAR AND INTERMOLECULAR FORCES OF ATTRACTION

Soap and water: when soap mixes with water, the soap gets between the intermolecular forces of the water molecules and reduces the surface tension. since the surface tension is reduced, the soap+water mixture can more easily cover more of a surface.

 In DNA (Deoxyribonucleic Acid) there are two strands made of nucleotides. each nucleotide in a strand is held together by covalent bonds, but the two large strands are held together by hydrogen bonds, which is weaker than covalent bonds. this intramolecular knowledge can be used in PCR, which is a biological technique that denatures the double strands using only heat, no enzymes. 







Honey and syrup are two products found in the kitchen and used for normal everyday use. they are both made up of simple sugars like sucrose. the sucrose is a carbohydrate, or polyhydroxylated aldehyde. in each sugar, there are hydroxyl groups, and between sugars these hydroxyl groups bond (hydrogen bond). there are SO many hydroxyl groups, that the bonds create a network of molecules. knowledge of both inter and intramolecular forces can be used in changing the viscosity of honey and/or syrup. by adding heat, the bonds can be broken, and then viscosity can be reduced.