Ionic Bonding

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

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

Three Types of Bonding Ionic Covalent Metallic electrons are transferred. Covalent electrons are shared. Metallic “sea of mobile electrons.”

Identify Bond Type from Formula Ionic Compounds metal + nonmetal Covalent Compounds nonmetal + nonmetal Metallic metal symbol Salts

Na metal  Cations Metals lose e-

Anions Nonmetals gain e- Cl2 (g) 

Ionic Compounds metal + nonmetal 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) metal + nonmetal

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

Strength of Ionic Bond Na+(g) + Cl−(g) → NaCl(s) Lattice Energy Energy released when one mole of an ionic crystalline compound is formed from gaseous ions. Na+(g) + Cl−(g) → NaCl(s) The experimental lattice energy of NaCl is −787 kJ/mol. Shown as negative value  Exothermic

Electron is transferred from Na to Cl Tiger Graphic

Oxidation Number Determines how many atoms are needed to form the ionic compound.

Properties of Ionic Compounds Memorize! High melting points Low vapor pressures Solids do not conduct electricity Melts (liquids) do conduct electricity Solutions (aq) conduct electricity electrolytes: substances whose water solution conducts an electric current. Tend to be hard and brittle High solubility in water.

Aside: What Conducts Electricity? ***MOBILE CHARGED PARTICLES*** If something conducts a current, it has some kind of mobile charged particles: either electrons (solids) or ions (solutions). If something doesn’t conduct, it doesn’t have particles that are both mobile and charged. Memorize this!

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

Bonding Character