Electron Transfer to form Ionic Bonds: • Ionic bond-­‐ the attractions between ions that hold them together in an ionic compound • Lattice energy-­‐ energy released by the imaginary process in which isolated ions come together to form a crystal or ionic compound • Octet rule-­‐ an atom tends to gain or lose electrons until its outer shell has eight electrons • Lewis symbol-­‐ the symbol of an element that includes dots to represent the valence electrons of an atom of the element Electron Sharing to form Covalent Bonds: • Covalent bond-­‐ a chemical bond that results when atoms share electron pairs • Bond length-­‐ the distance between two nuclei that are held by a chemical bond (also known as bond distance) • Bond energy-­‐ the energy needed to break one mole of a particular bond to give electrically neutral fragments • Electron pair bond-­‐ a covalent bond • Lewis structure-­‐ a structural formula drawn with Lewis symbols and that used sots and dashes to show the valence electrons and shared pairs of electrons (also known as a Lewis formula) • Single bond-­‐ a covalent bond in which a single pair of electrons is shared • Double bond-­‐ a covalent bond in which two pairs of electrons are shared • Triple bond-­‐ a covalent bond in which three pairs of electrons are shared Electronegativity and Polarity: • Partial charge-­‐ charges at opposite ends of a dipole that are fractions of full 1+ or 1-­‐ charges • Polar covalent bond-­‐ a covalent bond in which more than half of the bond’s negative charge is concentrated around one of the two atoms (also known as polar bond) • Dipole-­‐ partial positive and partial negative charges separated by a distance • Polar molecule-­‐ a molecule in which individual bond polarities do not cancel and in which, therefore, the centers of density of negative and positive charges do not coincide Dipole moment-­‐ the product of the sizes of the partial charges in a dipole multiplied by the distance between then; a measure of the polarity of a molecule • Electronegativity-­‐ the relative ability of an atom to attract electron density toward itself when joined to another atom by a covalent bond • Nonpolar covalent bond-­‐ an electron pair bond at the ends of which are atoms of equal or very nearly equal electronegativity • Ionic character-­‐ the extent to which a covalent bond has a dipole moment and is polarized Lewis Structures: • Bond order-­‐ the net number of pairs of bonding electrons. Bond order = ½ x (number of bonding e-­‐ -­‐ number of antibonding e-­‐) • Formal charge-­‐ the apparent charge on an atom in a molecule or polyatomic ion as calculated by a set of rules that generally assign a bonding pair of electrons to the more electronegative of the two atoms held by the bond Resonance: • Resonance structure-­‐ a Lewis structure that contributes to the hybrid structure in resonance-­‐stabilized systems; a contributing structure • Resonance hybrid-­‐ the actual structure of a molecule or polyatomic ion taken as a composite or average of the resonance or contributing structures • Resonance energy-­‐ the difference in energy between a substance and its principal resonance structure •