The field of a permanent induces a Dipole-induced dipole forces: o dipole in a non-polar atom or molecule. Due to charge fluctuations of the atoms there is an Dispersion force: o instantaneous displacement of the center of positive charge against the center of the negative charge. Thus at a certain moment a dipole exists and induces a dipole in another atom. Therefore non-polar atoms (e.g. neon) or molecules attract each other. Table 1: Short Range Interaction Forces Nature of Type of Force Energy Distance Bond (kcal/mol) Ionic bond Coulombic force 180 (NaCl) 2.8 Å 240 (LiF) 2.0 Å Covalent Electrostatic force 170 (Diamond) N/A (wave function overlap) 283 (SiC) N/A bond Metallic free valency electron sea 26 (Na) 4.3 Å bond interaction 96 (Fe) 2.9 Å (sometimes also partially 210 (W) 3.1 Å covalent (e.g., Fe and W) Hydrogen a strong type of 7 (HF) directional Bond dipole-dipole interaction Van der (i) dipole-dipole force 2.4 (CH4) significant Waals (ii) dipole-induced dipole in the force range of a (iii) dispersion forces few Å to (charge fluctuation) hundreds of Å Types of intermolecular forces
o Dipole-induced dipole forces: The field of a permanent induces a dipole in a non-polar atom or molecule. o Dispersion force: Due to charge fluctuations of the atoms there is an instantaneous displacement of the center of positive charge against the center of the negative charge. Thus at a certain moment a dipole exists and induces a dipole in another atom. Therefore non-polar atoms (e.g. neon) or molecules attract each other. Table 1: Short Range Interaction Forces Nature of Bond Type of Force Energy (kcal/mol) Distance Ionic bond Coulombic force 180 (NaCl) 240 (LiF) 2.8 Å 2.0 Å Covalent bond Electrostatic force (wave function overlap) 170 (Diamond) 283 (SiC) N/A N/A Metallic bond free valency electron sea interaction (sometimes also partially covalent (e.g., Fe and W) 26 (Na) 96 (Fe) 210 (W) 4.3 Å 2.9 Å 3.1 Å Hydrogen Bond a strong type of directional dipole-dipole interaction 7 (HF) Van der Waals (i) dipole-dipole force (ii) dipole-induced dipole force (iii) dispersion forces (charge fluctuation) 2.4 (CH4) significant in the range of a few Å to hundreds of Å Types of intermolecular forces
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