Dr. Lori Stepan Van Der Sluys 1 Chapter8 Part 1 Chapter 8 Part 1: Ionic Bonding Read: BLB 2.7–2.8; 8.1–8.2 HW: BLB 2: 51, 53, 57, 59, 65, 67; 70, 71 8:16, 22, 25 Sup 2:4, 5; 8:1 Know: Ionic Bonding • Lewis Symbols • Nomenclature • Lattice energy Bonus deadline for Skill Check Tests Approaching?? ____________________________________________ When is Exam 1??____________________________ ! Data sheet and periodic table in the packet will be provided during the exam Bring: pencils, student ID and a calculator—NO text-programmable calculators or wireless devices Dr. Lori Stepan Van Der Sluys 2 Chapter8 Part 1 • IONIC electrons traded to form separate ions both have noble gas __________ Na+ Cl! • COVALENT electrons shared between a few nuclei distinct molecules ______ e ! ____ e! • METALLIC electrons shared among all nuclei _________ e! __________ e ! “sea of electrons”Dr. Lori Stepan Van Der Sluys 3 Chapter8 Part 1 For ionic and covalent bonding: Keep track of electrons with Lewis Dot Symbols 1. ______________ electrons are involved in bonding; represent each electron with one dot . C · C · · 4 valence electrons . S [Ne] 3s2 3p4 :S: · ____ valence electrons 2. Octet rule: elements tend to gain, lose or share electrons so as to gain an _____________ configuration of 8 electrons. (Duet for H and He instead of octet) " Inert gases have 8 valence electrons Dr. Lori Stepan Van Der Sluys 4 Chapter8 Part 1 Knowing the Number of Valence Electrons, You Should be Able to Draw These:Dr. Lori Stepan Van Der Sluys 5 Chapter8 Part 1 Ionic Bonding Involves Transfer of _____________ to form charged _____________ Dr. Lori Stepan Van Der Sluys 6 Chapter8 Part 1 IONIC BONDING Ionic bond is due to electrostatic attraction. Coulomb's Law: Q1 - charge on 1st atom Q2 - charge on 2nd atom d - distance between charges Electrons are exchanged to from separate ions with complete _____________. Na+ Cl! 1s2 2s2 2p6 1s2 2s2 2p6 3s23p6 [Ne] [Ar] complete octets IONIC COMPOUNDS • distinct +/! ions • # crystal lattice • strong omnidirectional electrostatic bonds Characteristics 1. low electrical conductivity as solids (high as liquids) 2. very high melting, boiling points 3. hard but brittle 4. soluble only in polar solvents (water)Dr. Lori Stepan Van Der Sluys 7 Chapter8 Part 1 Ionic compound: a compound that consists of positive and negative ions. Metal + nonmetal Examples: NaCl K2SO4 Mg(NO3)2 NH4Cl Ionic compounds have ________ melting points and are brittle (many are ________). Molecular compounds: compounds consisting of individual molecules All nonmetals or nonmetals plus metalloids. Examples: HCl H2O CH3COOH NH3 Molecular compounds usually have _______ melting points (many are _______ or __________). Dr. Lori Stepan Van Der Sluys 8 Chapter8 Part 1 Naming Inorganic Compounds and Ions See Section 2.8Dr. Lori Stepan Van Der Sluys 9 Chapter8 Part 1 Figure 2.26 Figure 2.27 Figure 2.28 Dr. Lori Stepan Van Der Sluys 10 Chapter8 Part 1 Be able to fill in information as in the table below: Name Formula potassium ion CO32! ammonium ion sodium bicarbonate H2SO4 Combine Ca+2 and PO43! Cu(II) and sulfate ionDr. Lori Stepan Van Der Sluys 11 Chapter8 Part 1 Formation of ionic salts from the elements is very exothermic. Na+(g) + Cl!(g) $ NaCl(s) %H = -788 kJ/mol BUT • Removing an electron from a metal is __________________. Na(g) $ Na+(g) +e- %H = +496 kJ/mol • And adding an electron to a non-metal is moderately ______________. Cl(g) +e- $ Cl- (g) %H = -349 kJ/mol Overall the process seems like it would be endothermic. Why is formation of an ionic salt so favorable? The added stability is due to the attraction of the ions for each other. The attraction brings the ions close, releases energy, and forms a ________________. Dr. Lori Stepan Van Der Sluys 12 Chapter8 Part 1 Strength of Ionic Bond (Lattice Energy) Lattice Energy measures the strength of the ionic interaction. Definition: NaCl(s) $Na+(g) + Cl!(g) %H = +786 kJ/mol = Lattice Energy • LE cannot be determined experimentally • Use Hess’ Law (and known atomic properties) to get the value of the lattice energy. Born-Haber Cycle • By Hess's Law, the enthalpy of formation is equal to the sum of the energies of several individual steps. • Reasons for the stability of ionic compounds is made clear.Dr. Lori Stepan Van Der Sluys 13 Chapter8 Part 1 Lattice Energy NaCl E = 786kJ MgO E =3934kJ Why the big difference??? Different salts have different Q’s and d's NaCl MgO Radii Na+ 0.97Å Mg+2 0.66Å Cl ! 1.81Å O!2 1.40Å 2.78Å 2.06Å d is ______ for MgO SO: lattice energy for MgO is more than 4x greater dQQE21! Dr. Lori Stepan Van Der Sluys 14 Chapter8 Part 1 Salts and Ionic Lattices ION SIZES: Ion sizes are important in ionic bonds NaF 993oC NaCl 801oC larger NaBr 747oC anion NaI 661oC MgO 2800oC higher charge Trends: Melting point increases as charge _________________. Melting point increases as lattice energy _________________. Melting point increases as size _________________.Dr. Lori Stepan Van Der Sluys 15 Chapter8 Part 1 Which one of the following expresses the correct relationship between the melting points of the 3 ionic solids NaCl, MgS, and BaS? 1 NaCl > MgS > BaS 2 NaCl > BaS > MgS 3 MgS > BaS > NaCl 4 MgS > NaCl > BaS 5 BaS > MgS >
View Full Document
Unlocking...