January 23 2017 Chapter 11 Chapter 12 HW due Fri Feb 3rd SLW meets this week Homonuclear Diatomic Molecules of the Period 2 Elements Homonuclear diatomic molecules are those molecules composed of two identical atoms Example N2 O2 H2 etc What about Li2 In general only valence orbitals interact enough to form MO s Figure 11 17A Li2 Li2 bond order 1 Molecular Orbitals from Atomic p Orbital Combinations End to end combinations of a pair of 2p orbitals give s2p and s 2p Side to side combinations of a pair of 2p orbitals give p2p and p 2p Order of Energy Levels for MOs 2s orbitals are lower in energy than 2p orbitals same for AOs and MOs When six 2p orbitals from two atoms combine Two 2p orbitals combine to form s2p and s2p MO s Four 2p orbitals combine to form two p2p and two p2p MO s The order of filling the MO energy levels s2p p2p p 2p s 2p Orbital mixing Atoms of B C and N are sufficiently large that some s and p AO inter mixing occurs and this inter mixing results in the lowering of the p2p energy below the s2p with 2s 2p mixing p2p s2p p 2p s 2p MO energy levels for B2 C2 and N2 Bonding in the p Block Homonuclear Diatomic Molecules higher bond order correlates with greater bond energy and shorter bond length orbital occupancy correlates with magnetic properties paramagnetic diamagnetic Sample problem 11 4 Which has stronger bonds N2 N2 O2 2p 2p p 2p Bond order Bond energy kJ mol O2 p 2p 2p p2p p2p 2p 2s 2s 2s 2s 2 5 2 2 5 841 498 623 3 945 According to MO theory what is the bond order of the C2 cation A 1 5 C2 7 valence electrons B 2 2p C 2 5 p 2p D 3 2p E 3 5 p2p 2s 2s Bond order 5 2 1 5 Chapter 12 Intermolecular Forces Liquids Solids and Phase Changes All matter occurs in one of three physical states phases Solid Liquid Gas 12 1 An Overview of Physical States and Phase Changes Each physical state of matter is a phase a physically distinct homogeneous part of a system The properties of each phase are determined by the balance between the potential and kinetic energy of the particles The potential energy in the form of intermolecular forces draws molecules together The magnitude of the potential energy depends on the charges of the particles and distances between them Coulomb s Law The kinetic energy associated with the random motion of particles tends to disperse them The magnitude of the kinetic energy is proportional to the temperature of the system A Kinetic Molecular View of the Three States 2 types of electrostatic forces Intramolecular or bonding forces are found within a molecule They influence the chemical properties of the substance Intermolecular or nonbonding forces are found between molecules They influence the physical properties of the substance Figure 5 1