Chapter 10 The chemical bond when two atoms share a pair of electrons the transfer of electrons from one atom to another and the Valence shell electron pair repulsion model a link between atoms the theory of the origin of the numbers strengths and Chemical bond Valence theory three dimensional arrangements of chemical bonds between atoms Ionic bond consequent attraction between the ions so formed Covalent bond shape of a molecule to the repulsions between electron pairs in the valence shell much heavier than an electron move relatively slowly and may be treated as stationary while the electrons move around them molecule depends on the internuclear separation Equilibrium bond length curve the internuclear separation at the minimum of the curve a graph showing how the energy of a it is supposed that the nuclei being so Born Oppenheimer approximation a model used to ascribe the Molecular potential energy o The narrowness of the potential well is an indication of the stiffness of the bond Valence bond theory 10 1 Diatomic molecules a Formulation of the VB wavefunction The wavefunction for several noninteracting particles is the product of the wavefunctions for each particle b The energy of interaction internuclear repulsion At intermediate internuclear separations the attraction dominates the o At very short distances the repulsion dominates the attraction c and bonds bond a VB wavefunction with cylindrical symmetry around the a VB wavefunction that when viewed along the internuclear axis internuclear axis bond resembles a pair of electrons in a p orbital 10 2 Polyatomic molecules a Promotion Promoted empty atomic orbital movement of a valence electron from a full atomic orbital to an b Hybridization sp sp sp hybridized mixtures of atomic orbitals on the same atom a hybrid that is built from s orbital and three p orbitals Hybrid orbitals 3 hybrid 2 hybrid orbitals a combination of an s orbital and a p orbital The hybridization of N atomic orbitals always results in the formation of N when an s orbital and two p orbitals interact hybrid orbitals c Resonance Resonance the superposition of contributing structures d The language of valence bonding and bonds are formed by spin pairing of electrons on adjacent atoms Valence electrons may be promoted to empty orbitals if overall that results in Atomic orbitals may be hybridized to match the observed geometry of a a lowering of energy molecule The superposition of individual structures resonance distributes multiple bond character over the molecule and lowers the overall energy Molecular orbital theory 10 3 Linear combinations of atomic orbitals Molecular orbital a one electron wavefunction for an electron that spreads throughout the molecule If there are several possible outcomes of an observation then we add together the wavefunctions that represent each outcome The squares of the coefficients in a linear combination of atomic orbitals tell us the relative properties of the atomic orbitals contributing to the molecular orbital a Bonding orbitals orbitals electron Bonding orbital an orbital that resembles an s orbital when viewed along the axis an electron that occupies a orbital strength of a bond between two atoms a molecular orbital that if occupied contributes to the b Antibonding orbitals Nodal plane Antibonding orbital bond between two atoms a plane on which the wavefunction passes through zero an orbital that if occupied decreases the strength of a c Inversion symmetry Inversion symmetry through the center of the molecule the behavior of the wavefunction when it is inverted 10 5 Heteronuclear diatomic molecules Polar bond by the two atoms a covalent bond in which the electron pair is shared unequally a Polarity and electronegativity Electronegativity it is part of a compound the power of an element to draw electrons to itself when An atom that has a high electronegativity is likely to also have a high ionization energy and a high electron affinity Partial negative charge a net negative charge o This is balanced by a partial positive charge on another atom o The more electronegative element has the partial negative charge b Molecular orbitals in heteronuclear species The atomic orbital with the lower energy that belonging to the more electronegative atom makes the larger contribution to the lowest energy molecular orbital