Chapter #9: Chemical Bonding- Lewis Model9.2 Types of Chemical Bonds- Chemical bonds form because they lower potential energy of atoms.- In chemical bonds, electrons of one atom is attracted to nucleus of another atom.- However nucleus repel nucleus and electrons repel electrons. If interactions lead to net reduction of energy, bonds form.- Three types of bond: Covalent, ionic, and metallic.- Ionic bond is between metal and nonmetal where electrons are transferred.- Covalent bond is between nonmetals where electrons are shared.- Metallic bond is between metals where electrons are delocalized.9.3 Representing Valence Electrons- Valence electrons are the most important in bonding because they are held the most loosely.- Lewis symbol is representing valence electrons by dots around the abbreviation of the element.- If it has a full outer level, eight electrons, it is an octet.- Helium is an exception that only needs 2 electrons (duet).- Octet rule is bonding atoms to obtain a stable electron configuration of eight valence electrons.- Lewis structure does not calculate energy changes in chemical bonding.9.4 Ionic Bonding: Lewis Symbols and Lattice EnergiesIonic Bonding and Transfer- Lewis structures are usually used to represent covalent bonds but it can also be used for ionic bonds.- Transfer valence electron from metal to nonmetal and include the charges with brackets.- If there are more than one atom of an element in the bonding, add the number of the atom needed in front of Lewis structure.Lattice Energy- Formation of ionic compounds are exothermic.- The transfer of electrons actually require energy.- Lattice energy is the energy needed to form the crystalline lattice of cations and anions from gaseous ions.- When anions and cations come together, it decrease in potential energy according to Coulomb’s law and this energy is emitted as heat.Born-Haber Cycle- Born-Haber cycle is the series of steps in the formation of an ionic compound that can be used to calculated the lattice energy.- Use Hess’s Law to determine lattice energy from the other energies given.- First step is to form gaseous metal from solid.- Second step is to make nonmetal molecule to atom.- Third step is ionization of gaseous metal. (ionization energy)- Fourth step is addition of electron to gaseous nonmetal. (electron affinity)- Last step is the formation of crystalline structure from the ions. This enthalpy change is the lattice energy.- Lattice energy is NEGATIVE!Trends of Lattice Energy- Lattice energy decrease down column of periodic table.- Ionic radii increase down table so there are more distance between ions and according to Coulomb’s law the potential energy decrease. Thus not as much energy is released when lattice form.- Magnitude of potential energy depend on charges so with the increase in ionic charge, the greater the lattice energy.- Ionic charge can estimate how many time greater one compound’s lattice energy is in comparison to another.Ionic Bonding: Models and Reality- Ionic solid is modeled with a lattice and the coulombic forces that holds the ions together must be overcome to melt. Thus, high melting point.- Electrons remain localized on one atom after transfer so no free electrons for conductivity.- When ionic solid dissociates in water, the free ions can move and create electrical current. Can conduct