Carbon Chemistry
Introduction to Carbon Chemistry:
Intermolecular Forces * Intermolecular forces increase as the states go from gas → liquid → solid. Thus, increasing/decreasing temperature can change the forces and increasing the pressure increases the forces. * Intermolecular forces are the attractive forces between molecules, ion and ions and molecules. * Without intermolecular forces all substances would be gases. * Intermolecular forces are weaker than intramolecular forces (i.e. bonding). Thus, less energy is required to break intermolecular forces than intramolecular forces. * Types of forces in decreasing order of strength: * Ion-ion attraction * Ion-dipole attraction * Dipole-dipole attraction * Dipole-induced dipole attraction * Induced dipole – induced dipole attraction (London dispersion forces) * DIPOLE-DIPOLE * Dipole-dipole forces exist between polar molecules. * The partial charges of one molecule can attract the partial charges of a neighbour. * The strength of the interaction depends on the magnitudes of the bond dipoles and the shape of the molecule. * For molecules of approx equal molecular mass and size, intermolecular attractions increase with increasing polarity. * Thus, boiling point increases with increased polarity. * Hydrogen Bonding * Attraction between the hydrogen atom in a polar bond. * H is attached to a very electronegative atom. * Electronegativity increases as you go along and up the periodic table. * Hydrogen bonding is very strong (stronger than ordinary dipoles) as H is small and can get very close to an electronegative ion. * The strongest hydrogen bond occurs between molecules of HF (biggest difference in electronegativity), then H2O and NH3. * Can also bond with HCl and H2S, but to a lesser extent. * Generally, the boiling point increases with an increase in molecular weight, this is not the case when hydrogen bonding is present. * Hydrogen bonding is a much stronger attractive force than normal dipole-dipole forces, which elevates the boiling point. * SOLUBILITY * The general rule is “like dissolves like”, i.e. two polar liquids will mix together/are soluble (e.g. water and ethanol), while a polar and a non-polar compound will not/are not soluble in each other (water and hexane). * INDUCED DIPOLE-INDUCED DIPOLE * AKA dispersion forces or London forces. * Range from weak to relatively strong. * Non-polar molecules must have some attraction to each other or they would not turn into solids. Thus, the motion of electrons in an atom/molecule can create an instantaneous/momentary dipole moment. * The dipole moment of one atom/molecule affects its neighbours, temporarily inducing a similar dipole moment on an