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The greek symbol  indicates “partial charge”. H2H2 HClLiCl ++ –– 00 00 +– 1. Non-polar covalent 2. Polar covalent3. Ionic HH H Cl [Li] + [ Cl ] –

The polarity of a molecule depends on the polarity of its bonds and the shape (symmetry) of the molecule. Molecules have different shapes based on their electron arrangements.

 Intramolecular forces (Ionic and covalent bonds)  strong attraction  An intermolecular force is an attraction that occurs between molecules  weak attraction

Intermolecular forces dictate the physical properties of molecular compounds:  State of matter  Surface Tension  Hardness and Texture  Solubility in Various Solvents  Melting and Boiling Point

 If enough energy is added, this weak attractive force will be broken and molecules will be set free from one another  Strong the intermolecular forces:  Requires more energy to break  The higher the boiling point

1. London Dispersion Forces 2. Dipole-Dipole Forces 3. Hydrogen Bonding

 Intermolecular attraction found in all molecular compounds (polar & non polar)  Involves a temporary shift in electron clouds at one end of the molecule  leads to a temporary dipole within the molecule  This temporary shift causes an induced shift in electrons in the adjacent molecule (due to electrostatic interaction)

Original Temporary dipole Induced Temporary dipole

 This is the weakest intermolecular force  The strength of these forces depends on: 1. Number of electrons in an atom  The greater the electrons, the greater chances for shifting charge 2. Ease to disperse electrons  The electrons are to the nucleus, the easier it is to disperse  Greater number of electrons  Strong attraction  Higher Boiling Point

 Intermolecular attraction found only in polar molecules  Attraction between the positive end of one polar molecule and the negative end of an adjacent polar molecule  Stronger than London Dispersion Forces

 DIPOLE FORCES OVERPOWER LONDON FORCES (STRONGER)  HIGHER MELTING POINT  HIGHER BOILING POINT

 Strong type of Dipole force  Occurs when a hydrogen is bonded to a very electronegative atom (ie: F, O, N)  HF, H2O, NH3

 Hydrogen bonds are the strongest dipole force because: 1. The ∆EN between H and a highly electronegative atom causes electrons to travel away from the H  behaves like a proton 2. Small size of H can fit closely with the negatively charged side of an adjacent molecule

 Hydrogen bonds are formed between the nucleotides that join the two strands of DNA together. Forming a helical structure.

BOND OR FORCEDISSOCIATION ENERGY (kJ) Ionic Bond>600 kJ Covalent Bond Hydrogen Bonds16-70 Dipole-Dipole Forces London Dispersion Forces<4.0