Chapter 8 Ionic Compounds I. Forming Chemical Bonds – How do Compounds Form? • Stability • Compounds want to have a noble gas configuration (8 valence electrons) I. Why do atoms form bonds? Chemical Bond - strong attractive force between atoms or ions in a compound. • stability - goal is to reach the most energetically favorable condition • bond energy - energy involved in process of bond forming or bond breaking • Valence Electrons outermost electrons Highest Energy Level Valence Electrons? 3s23p6 How do you represent Valence Electrons? Electron Dot Structures 1. What is the atomic number of this element? 2. Write the electron configuration. 3. Identify just the valence electrons (hint use the “A” roman numerals on the periodic table). How do you represent Valence Electrons? Electron Dot Structures 4. 5. Write the symbol for the element. Use a dot for each valence electron. An element with a complete valence shell (8 e-) will look like this: X Try these examples: Li B N F Be C O Ne 1. shows valence electrons, for example lets try these…… Li B N F Valence electron C O Ne Be Stable Octet (new words, octet rule): 8 electrons in valence shell, stable configuration II. Ionic Bonding: process by which one or more electrons are transferred from the valence shell of one atom to the valence shell of another atom. (usually forms salts) Unstable 3s1 3p5 3s2 Electons Transferred = ionic bond Stable 11P+ 10e1+charge Electrostatic attraction full octets 17P+ 18e1- charge Ionic Bonding 8.3. Names and Formulas for Ionic Compounds (8.3 pgs. 221-227) A. Formulas tell: 1. which elements make up the compound (qualitative) 2. ratios of atoms contained (quantitative) Hydrogen & Oxygen in element H 2O # of H’s and O’s in molecule B. Made from a metal + a nonmetal 1. metals form (+) ions - cations 2. nonmetals form (-) ions - anions C. Using ion charge to write formulas 1. write the chemical symbol 2. using the periodic table assign a charge (to be written as a subscript) Group 1+ IA, 2+ IIA, 3+ IIIA, 3VA, 2VI, 1VIIA 3. add charges together to equal zero, use charge of one ion as subscript for the other ion, or use criss-cross method 4. when subscripts are equal they reduce to 1 5. for polyatomics (more than one atom combined that has an overall charge), use parenthesis when subscript is 2 or more examples: Calcium chloride Ca2+ + Cl1- + Cl1- = 0 CaCl2 examples: Calcium chloride CaCl2 Aluminum oxide Magnesium phosphate Barium sulfate Al2O3 Magnesium sulfide MgS Ammonium chloride examples: Magnesium phosphate Mg32+ PO43-2 Mg3(PO4)2 examples: Barium sulfate BaSO4 Ammonium chloride NH4Cl D. Naming ionic compounds 1. binary compounds - two different kinds of atoms a. name the first element b. name the second element,drop the last syllable, add -ide. examples: Na2S = Sodium Sulfide MgO = Magnesium Oxide Naming ternary compounds 2. ternary compounds - name the first element, then name the polyatomic ion examples: Ca(NO3)2 = Calcium Nitrate Na2SO4 = Sodium Sulfate E. atoms that form more than one type of ion (examples: Cu, Fe, Hg, Pb, Sn) 1. old system - call the ion with the greater charge -ic, and the ion with the lesser change -ous. (use Latin names as roots) Cu+1 Cu+2 Fe+2 Fe+3 cuprous cupric ferrous ferric CuF CuF2 FeF2 FeF3 cuprous fluoride cupric fluoride ferrous fluoride ferric fluoride 2. new system (or stock system), name ion by atom. The name is followed by roman numeral telling its charge. Cu+1 copper(I) ` CuF copper (I) fluoride Cu+2 copper(II) CuF2 copper (II) fluoride Fe+2 Iron(II) FeF2 iron (II) fluoride Fe+3 Iron(III) FeF3 iron (III) fluoride III. Properties of Ionic Compounds: Crystal Lattice- three dimensional arrangement of cations & anions List Properties here • Crystal shape • Hard & brittle • High melting pt • High boiling pt • When dissolved, or molten, conducts electricity Properties of Ionic Solids Electrons transferred = ionic bond Electrostatic Attraction Crystal shape Unit cell – simplest, repeating unit IV. Energy and the Ionic Bond: • During any chemical or physical reaction energy is neither created or destroyed • Energy that is absorbed is called endothermic • Energy that is release is called exothermic • The formation of ionic compounds from positive and negative ions is always exothermic. The compound formed is more stable and of lower energy. IV. Energy and the Ionic Bond: • The energy required to separate one mole of the ions of an ionic compound is referred to as the lattice energy. • The more negative the lattice energy, the stronger the force of attraction. • Which would have more negative lattice energy, lithium chloride or lithium bromide? Lithium chloride • MgO is almost four times greater then the lattice energy of NaF, why? MgO, charge of the ions is greater V. Names and Formulas for Ionic Compounds(8.3 pgs. 221-227)(see previous notes) !Describe a Pot of Gold (physical and chemical properties of the pot and the gold coins) High luster High Melting/Boiling Pt. Malleable Ductile Solid Conductive VI. Metallic Bonds and Properties of Metals (8.4 pgs. 228-231) 1. Metals form a lattice with eight to 12 other metal atoms surrounding each metal atom. 2. metals have at least one valence electron, they do not form ions or share their electrons 3. metals are crowded with electrons and the outer energy levels of the metal atoms overlap VI. Metallic Bonds and Properties of Metals (8.4 pgs. 228-231) 4. The electron sea model proposed that all the metal atoms in a metallic solid contribute their valence electrons dot form a “sea” of electrons. 5. Electrons are not held tightly by any specific atom, electron are free to move around and are referred to delocalized electrons. 6. The attraction of a metallic cation for delocalized electrons is called a metallic bond. Properties of Metallic Bonding
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