CHAPTER 14
POLAR MOLECULES

14-1 Polarity a polar covalent bond occurs when a shared pair of electrons is attracted more strongly to one of the atoms in the bond dipole is another name for polar molecule dipole moment depends upon the size of the partial charges and the distance between them melting point and boiling point are related to dipole moment

14-2 Weak Forces weak attractive forces between the protons of one atom and the electrons of another atom are Van Der Waals forces intramolecular forces hold atoms together in a molecule intermolecular forces hold different molecules together While chemical bond energies range from about 200-800 kj/mol, weaker dipole-dipole forces are less than 125 kj/mol a nonpolar molecule may become an induced dipole 2 nonpolar molecules may be attracted to each other dispersion forces result from temporary dipoles Van Der Waals attraction can result from any of the following dipole-dipole forces/ dipole-induced dipole forces/ dispersion forces

14-3 Ligands a complex ion is formed when polar molecules or negative ions cluster around a central positive ion. ligands are the polar molecules or negative ions that are attached to the central positive ion water is the most common ligand a bidentate ligand attaches to 2 points the number of ligands surrounding the central ion in a complex is called the coordination number

14-4 Names and Formulas of Complex ions use the prefixes of di-,tri-,tetra-,penta-,hexa- to indicate the number of each kind of ligand in a name complex ions are named as follows: ligands first, in alphabetical order with prefixes if needed central ion -ate ending, if ion is negative roman numeral if needed ligands in the formulas of complex ions are written in a different order form ligands in the names

14-5 Coordination Compounds it is possible to have a complex with a net charge of zero in a coordination compound if a complex ion occurs in the formula of a coordination compound place the whole complex in brackets a coordination compound consists of a complex ion and other ions (anions and cations) or a neutral central atom and neutral ligands combined to form a compound with no net charge

14-6 Bonding in Complexes Œtransition metals have partially filled d orbitals that can become involved in bonding the bonding structure of complex ions is similar to that of salt the bond formed when both electrons in the shared pair come from the same atom is a coordinate covalent bond

14-7 Fractionation chromatography is a separation method that depends on the polarity of substances in chromatography the mobile phase or mixture to be separated passes over the stationary phase

14-8 Chromatography thin layer chromatography combines column and paper chromatography techniques gas chromatography is used to analyze volatile liquids and mixtures of gasses chromatography is a method of separating a mixture of substances into identifiable chemical fractions based on differences in polarity of the individual fractions