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Ionic Bonding aka Electrovalent bonds Ionic Bond Chemical bond resulting from electrostatic attraction between positive and negative ions. – Goal: achieve stable octet of electrons (noble gas configuration) Illustrate by – Orbital notation – Lewis Dot diagrams Three Types of Bonding Ionic – electrons are transferred. Covalent – electrons are shared. Metallic – “sea of mobile electrons.” Identify Bond Type from Formula Ionic Compounds – metal + nonmetal Covalent Compounds – all nonmetals Metallic – all metals Force of Attraction Show transfer of VALENCE electrons to achieve octet But WHICH electrons (i.e. what orbitals) are involved? Formation of The Octets A quantum mechanical representation of the electron transfer Na metal Metals lose e- Nonmetals gain e- Cl2 (g) Ionic Compounds Composed of positive and negative ions combined so that compound is NEUTRAL. Most ionic compounds are … crystalline solids. Expressed as Formula Units, not molecules (which are covalent)! – Simplest ratio of atoms (empirical formula) Structure of Ionic Compounds Ions are attracted to each other by strong electrostatic interactions. Form a crystal lattice – a regular 3-D pattern or array. – Ions are held in fixed positions in the solid state. Unit Cell = smallest repetitive unit in lattice Electron is transferred from Na to Cl Tiger Graphic Ionic Reactions Strength of Ionic Bond Lattice Energy – Energy released when one mole of an ionic crystalline compound is formed from gaseous ions. Na+(g) + Cl−(g) → NaCl The experimental lattice energy of NaCl is −787 kJ/mol. Shown as negative value Exothermic Trends in Lattice Energy Lattice Energy* and Interionic Distance Interionic Distance as Lattice Energy Decreases Lattice Energy (kJ/mol)* Increases 1100 1050 1000 950 900 LiF 850 LiCl 800 750 LiI 700 209 * positive values show n 257 Interionic Distance (pm ) 296 Trends in Lattice Energy * positive values show n Ionic Compound State the trend here… Ki KC l KB r KF Na I Na Cl Na Br Na F Li I r Li B Li C l 1200 1000 800 600 400 200 0 Li F Lattice Energy (kJ/mol)* Lattice Energy*and Compound Size Factors that Affect Lattice Energy Related bonded. to the SIZE of the ions – Smaller ions generally have a more negative (larger) lattice energy. Affected by the CHARGE on the ion. – Larger charged atoms generally have a more negative (larger) lattice energy Oxidation Number Determines how many atoms are needed to form the ionic compound. Ionic Bond Formation ENERGY Potential Energy Release Decreasing energy means greater stability! Na + Cl NaCl Properties of Ionic Compounds High melting points Low vapor pressures Solids do not conduct electricity Melts (liquids) do conduct electricity Solutions (aq) conduct electricity – electrolytes: Tend substances whose water solution conducts an electric current. to be hard and brittle High solubility in water. Linus Pauling 1954 Nobel Prize Chemistry First to show that chemical bonds could show degrees of both a covalent and ionic nature. Led to the development of electronegativity values. Electronegativity Difference 1.7 Electronegavitity Difference Bonding between atoms is a continuum from ionic to covalent. The larger the difference in electronegativity between two bonded elements, the more ionic in character the bond has. Which has more ionic character? – CaO or KF or LiH Crystal Coordination Number The coordination number of an atom in a molecule or a crystal is the integer number of its nearest neighbors. Salt Crystals - Cubic