Ionic Bonds: One Big Greedy Thief Dog! A. Covalent Bond HOW DOES IT WORK? Covalent bonding takes place between non-metals atoms only Atoms try to attain noble gas structure by sharing electrons The shared electrons are attracted by both nuclei and this attraction forms the covalent bond Atoms bonded in this way form molecules Nonpolar Covalent Bond e - are shared equally usually identical atoms A. Covalent Bond The Seven Diatomic Elements Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2 A. Covalent Bond Polar Covalent Bond e - are shared unequally between 2 different atoms results in partial opposite charges A. Covalent Bond Thats not fair! Polar Covalent Bonds: Unevenly matched, but willing to share. Nonpolar Polar Ionic C. Comparison Occurs in metals A metal consists of positive ions surrounded by a sea of moving electrons B. Metallic Bond Metallic Bonds: Mellow dogs with plenty of bones to go around. C. Comparison IONIC COVALENT Electrons Melting Point Soluble in Water Conduct Electricity Other Properties transferred from metal to nonmetal high yes (solution or liquid) yes crystal lattice of ions, crystalline solids shared between nonmetals low no usually not molecules, odorous liquids & gases ioniccovalent valence electrons C. Comparison sharing of electrons transfer of electrons ions molecules high mp low mp conductive non- conductive What can we learn about the properties of ionic and metallic substances by looking at their atomic structure? The sodium chloride crystal stays together due to (+) and (-) electrostatic attractions. etc Here is an example of a metallic crystal. Note its similarity to the organization of an ionic crystal. Here, however, all the ions are positive. HOW CAN THAT BE? How can (+) ions stick together? As an example metal, Lets take a look at aluminums subatomic structure ALUMINUM The aluminum particles are arranged in an orderly repeating pattern. ALUMINUM However the valence electrons are not localized to any one particle. They are free to move and occupy the space between the (+) ions. ALUMINUM Ionic Bond, A Sea of Electrons The large attraction of the (+) ions for the (-) delocalized valence electrons are what holds the crystal together. ALUMINUM The large attraction of the (+) ions for the (-) delocalized valence electrons are what holds the crystal together. ALUMINUM cations (+ ions) The large attraction of the (+) ions for the (-) delocalized valence electrons are what holds the crystal together. ALUMINUM cations (+ ions) The large attraction of the (+) ions for the (-) delocalized valence electrons are what holds the crystal together. ALUMINUM cations (+ ions) The large attraction of the (+) ions for the (-) delocalized valence electrons are what holds the crystal together. ALUMINUM freely moving valence electrons The large attraction of the (+) ions for the (-) delocalized valence electrons are what holds the crystal together. ALUMINUM freely moving valence electrons The large attraction of the (+) ions for the (-) delocalized valence electrons are what holds the crystal together. ALUMINUM freely moving valence electrons ALUMINUM Our example of aluminum metal consists of Al 3+ ions, with each Al atom giving up 3 electrons to the delocalized sea of electrons. How does this arrangement account for metallic properties? Lets look at malleability. 3+ The delocalized electrons are a constant presence, always holding together any shifting (+) ions. 3+ The delocalized electrons are a constant presence, always holding together any shifting (+) ions. 3+ This is malleability. Why arent ionic crystals malleable? Ionic crystals cleave because the like charges of shifted ions repel each other. The cleavage often results in a shear, smooth face between the split crystals. Back to metallic crystals! The strong attraction between the (+) ions in the crystal for the delocalized electrons results not only in malleability: This structure makes metals hard and strong, with a high melting point: This structure makes metals hard and strong, with a high melting point: The particles want to stay together! In general, the more delocalized electrons, the tougher the metal. Transition metals have the most delocalized electrons and are the strongest. Delocalized electrons also carry electric current and heat due to their ability to move through the crystal. AND delocalized electrons readily absorb and re-emit visible frequency photons, giving metals their characteristic luster. TOO COOL!!