Molecular Structure of Biological Systems (Inter-molecular and Intra-molecular Forces)
Physical properties of biological systems on the molecular level • Two kinds of physical behavior meet on the molecular level of biological • structures: • On the one hand, there are the characteristic properties of microphysical • processes, based on the individual behavior of single small particles like atoms, • molecules, or supramolecular structures. • These processes are mostly stochastic (non-deterministic so that the subsequent state of the system is determined probabilistically) . • On the other hand, there are reactions which resemble macrophysical properties, the • kind of behavior of “large” bodies. • Our daily experiences with macrophysical systems teach us that their behavior is generally deterministic.
Inter and Intra-molecular Forces • Intermolecular • Forces between a molecule • Is what attracts molecules to each other • Intramolecular • Forces within the molecule • Is what keeps molecules together
Intermolecular and Intramolecular forces • Intermolecular forces (IMF’s) • Attraction between 2 or more compounds (compound and another compound) • Intramolecular forces • Ionic attraction between cation/anions • Covalent Sharing valence electrons • Metallic Metals release electrons (alloys)
Intermolecular Forces and physical properties • The strength of intermolecular forces determines the following physical properties of molecular compounds; • Physical state of a compound • Melting point • Boiling point • Surface tension • Hardness and texture • Solubility
3 Main IMF’s • 1. Hydrogen bonds (H-Bonds) • 2. Dipole-Dipole • 3. London Dispersion Forces (Van DerWoals)
Intermolecular Forces ( Polar) Dipole-Dipole • Attraction between oppositely charged regions of Polar Molecules • Strong but not as strong as H-Bonds
Intermolecular Forces (Polar) Hydrogen Bonds (H-Bonds) • When a H atom of one molecule is attracted to a highly electronegative atom (F,O, N) • Strongest!! • H-Bonds- the more polar a molecule is, the stronger the dipole-dipole intermolecular forces are
Intermolecular Forces (Polar) Hydrogen Bonds (H-Bonds) • Three highest electronegativites on the periodic table : Fluorine, Oxygen, Nitrogen (NOF) • NOF bonded with/to Hydrogen you get big electronegativity difference. L.D.F, D-D & H-Bond
Intermolecular Forces (Non-Polar) London Dispersion Force (Van Der Waals) • Induced dipole between two non-polar molecules. • Temporary dipole • Short lived dipole • LDF = Weakest intermolecular force(10x weaker)
Intermolecular Forces (Non-Polar) Van Der Waals • No Dipole • Protons of one molecule can attract electrons from another molecule • Van Der Waals forces (LDF)- Non-polar. H2 (Non-Polar) H H LDF H H F2 (Non-Polar) • More protons & electrons means stronger intermolecular forces • Stronger LDF than H2 LDF • More energy to break apart F2 then H2 FF LDF FF
What do you see? • Dipole- Dipole attraction with (+) hydrogen and (-) chlorine • LDF between HCl molecules • This is a POLAR molecule • When there is a dipole-dipole and LDF = high B.P. H Cl
Difference between inter & intra molecular forces • Intermolecular forces are formed between molecules and intramolecular forces are formed within molecules • Intra molecular forces are much stronger compared to intermolecular forces • Covalent, Ionic and Metallic bonding are types of intramolecular forces • Dipole-Dipole, Dipole-Induced dispersion forces and hydrogen bonding are some of the examples of intermolecular forces.
Intermolecular Forces • Stronger intermolecular force = higher the melting and boiling point • When melting and boiling points are high = strength of bond is STRONG STONGEST WEAKEST LONDON DISPERSION FORCE (LDF) HYDROGEN BOND (H-BOND) DIPOLE- DIPOLE IONIC BONDS