Chapter 9 Ionic and Covalent Bonding 9 1 Describing Ionic Bonds Ionic Bond and negative ions A chemical bond formed by the electrostatic attraction between positive o Electrons are transferred from the valence shell of one atom to the valence shell of the other o Cation Atom that loses electrons positive ion o Anion Atom that gains electrons negative ion o Usually between an metal and nonmetal o Ex Sodium Atom Na Ne 3s1 Cl Ne 3s23p5 Na Ne Cl Ne 3s23p6 Symbol in which the electrons in the valence shell of an atom or ion are represented by Lewis Electron Dot Symbol dots Lattice Energy Properties of Ionic Substances distances 9 2 Electron Configurations of Ions Change in energy when an ionic solid is separated into isolated ions in the gas phase Ionic substances are high melting solids As you increase the temperature these atoms or ions vibrate through larger and larger Ionization Energy Energy needed to remove an electron o Increases across the periodic table and decreases down the periodic table o Protons increase from left to right so the nucleus and electrons have a stronger pull bringing the atom closer together therefore making it harder to remove an electron Electron Affinity Energy needed to gain an electron o Increases across the periodic table and decreases down the periodic table Polyatomic Ions Transition Metal Ions Ions held together by covalent bonds Most transition elements form several Cations o Ex Fe2 and Fe3 These elements are mostly colored main group are colorless 9 3 Ionic Radii ion table Ionic Radius Is the measure of the size of the spherical region around the nucleus of an o Decreases are you go across the periodic table and increases as you go down the o If you arrange isoelectronic ions by increasing nuclear charge then they will be in the order of decreasing ionic radius Ex O2 F Mg2 Isoelectronic Different species having the same number and configuration of electrons o Ex Na Mg2 Al3 Covalent Bonds A chemical bond formed by the sharing of a pair of electrons between two atoms Are shared between two nonmetals 9 4 Describing Covalent Bonds Bond length Bond dissociation Energy Distance between the nuclei at the minimum energy Energy that must be added o The larger the bond dissociation energy the stronger the bond Lewis Formulas Lewis Electron Dot Formula Bonding Pair Nonbonding Pair Lone Pair Coordinate Covalent Bond by one atom Octet Rule Single Bond Double Bond Triple Bond formula using dots to represent valence electrons an electron pair shared between two atoms Electron pair that remains on one atom and is not shared Bond formed when both electrons of the bond are donated Tendency of atoms in molecules to have 8 electrons in their valence shells Covalent Bond in which a single pair of electrons is shared by two atoms Covalent Bond in which 2 pairs of electrons are shared by two atoms Covalent Bond in which 3 pairs of electrons are shared by two atoms 9 5 Polar Covalent Bonds Electronegativity Covalent bond in which the bonding electrons spend more time Polar Covalent Bond near own atom than the other o Ex HCl Molecule electron to itself o Electronegativity is a measure of the ability of an atom in a molecule to draw bonding Electronegativity X half its ionization energy I E plus electron affinity E A Fluorine is the most electronegative tends to pick up electrons easily Large E A and In general electronegativity increases from left to right and decreases from top to hold on to them strongly large I E bottom in the periodic table o Metals are the least electronegative and nonmetals are the most electronegative The absolute value of the difference between in electronegativity between two bonded atoms gives a rough measure of the polarity to be expected in a bond o When this difference is small the bond is nonpolar o When this difference is big the bond is polar Electrons are pulled to the most electronegative atom 9 6 Writing Lewis Electron Dot Formulas 1 st Step 2 nd Step 3 rd Step 4 th step Calculate the total number of valence electrons Write the skeleton structure of the molecule or ion Distribute electrons to the atoms surrounding the central atom or atoms Distribute the remaining electrons as pairs to the central atom or atoms 9 7 Delocalized Bonding A type of bonding in which a bonding pair of electrons is spread Delocalized Bonding over a number of atoms rather than localized between two writing all possible electron dot symbols Resonance Formals the electron structure of a molecule having delocalized bonding by 9 9 Formal Charge and Lewis Formulas Formal Charge is the hypothetical charge you obtain by assuming that bonding electrons are equally shared between bonded atoms and that the electrons of each lone pair belong completely to one atom o Valence electrons minus the bonds lone pairs Each dash counts as 1 electron and lone pairs count as two Bond Length and Bond Order Bond Length or Bond distance is the distance between the nuclei in a bond Covalent Radius the value for the atom in a set of covalent radii assigned to atoms in such a way that the sum of the covalent radii of atoms A and F predicts the approximate A B bond length Bond Enthalpy Bond Enthalpy molecule in the gas phase A measure of the strength of a bond the average enthalpy change for the breaking of an A B bond in a o The larger the bond enthalpies the stronger the chemical bond Obtained from enthalpies of reaction delta H