A comparison of metals and nonmetals (Review) Review: Types of Chemical Bonding

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1 All course materials, including lectures, class notes, quizzes, exams, handouts, presentations, and other materials provided to students for this course are protected intellectual property. As such, the unauthorized purchase or sale of these materials may result in disciplinary sanctions under the ampus Student ode. A comparison of metals and nonmetals (Review) Review: Types of hemical Bonding Recognizing Ionic compounds: Metal plus nonmetal R Metal plus polyatomic ion R Two or more polyatomic ions Recognizing covalent compounds: ontains only nonmetal atoms We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 1 of 14

2 oncept heck Which of the following is an ionic compound? a. S 2 b. l 2 c. H 2 2 d. Ti 2 e. None of the above, all are covalent compounds The Ionic Bonding Model Why are ionic compounds brittle and crack? Properties of Ionic ompounds Ionic compounds tend to be hard, rigid, and brittle, with high melting and boiling points Ionic compounds do not conduct electricity in the solid state In the solid state, the ions are fixed in place in the lattice and do not move We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 2 of 14

3 Lewis Electron-Dot Symbols To draw the Lewis symbol for any main-group element: Determine the number of valence electrons (same as group number) Place one dot at a time on each of the four sides of the element symbol Keep adding dots until all valence electrons are represented Bonding Pairs and Lone Pairs / representation of covalent bonding Properties of a ovalent Bond The bond order is the number of electron pairs being shared by a given pair of atoms Single bond Double bond Triple bond bond energy (BE) is the energy needed break the bond and separate bonding atoms Lewis Dot structures: Molecules 1. ount valence electrons (sum of group numbers for all atoms) 2. Arrange around central atom (the 1 st element listed unless otherwise indicated) and complete octet of outside atoms 3. omplete octet of central atom(s). Use multiple bonds if necessary 4. Dump any extra electrons on the central atom Draw the Lewis dot structure of the following compounds H4 We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 3 of 14

4 NH3 NH4 + We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 4 of 14

5 Writing Lewis Structures for Molecules with More than ne entral Atom Write the Lewis structure for methanol (molecular formula H3H), an important industrial alcohol that is being used as a gasoline alternative in car engines Ethanol; H3H2H Exceptions to the ctet Rule We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 5 of 14

6 Write a Lewis structure and identify the octet-rule exception for SlF5 XeF4 BFl2 oncept heck Which of the following contains an atom that does not obey the octet rule? a. KBr b. 2 c. lf3 d. Il We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 6 of 14

7 Resonance Structures, Resonance Hybrids and Electron Delocalization Resonance structures have the same relative placement of atoms but different placements of e s Resonance forms are not real bonding depictions. In other words, 3 does not change back and forth between its resonance form Neither resonance structure alone depicts 3 accurately, because the oxygen-to-oxygen bonds are identical in length and energy. It is best represented as a resonance hybrid The Resonance Hybrid is an average of its contributing resonance forms Draw the Lewis dot structure(s) of the following compounds 2 N3 We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 7 of 14

8 Formal charges a way to keep score Rules for ordering resonance structures 1. Resonance structure with zero formal charges is most favored (most stable) 2. Resonance structures with +1 or 1 favored over those w/ +2 or 2 3. Two consecutive +1 and 1 are unfavorable 4. Resonance structures with 1 on most electronegative atom is preferred Draw all resonance structures for N, and then rank them according to the above rules I II III N N N Draw all resonance structures for N2, and then rank them according to the above rules I II III NA NB NA NB NA NB We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 8 of 14

9 Draw all resonance structures for l2, and then rank them according to the above rules I II III la lb la lb la lb Draw all resonance structures for S, and then rank them according to the above rules S S S We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 9 of 14

10 Bond Energies and H 0 rxn The heat released or absorbed during a chemical change is due to differences between the bond energies of reactants and products Using bond energies to calculate H 0 rxn for the combustion of methane H4(g) + 2 2(g) 2(g) + 2 H2(g) We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 10 of 14

11 Average Bond Energies (kj/mol) Bond BE Bond BE Bond BE Bond BE HH 432 NH 391 SiH 323 SH 347 HF 565 NN 160 SiSi 226 SS 266 Hl 427 NP 209 Si 368 SF 327 HBr 363 N 201 SiS 226 Sl 271 HI 295 NF 272 SiF 565 SBr 218 H 413 Nl 200 Sil 381 SI ~ NBr 243 SiBr 310 FF 159 Si 301 NI 159 SiI 234 Fl 193 N 305 H 467 PH 320 FBr P 351 PSi 213 FI 263 P PP 200 ll 243 S 259 S 265 PF 490 lbr 215 F 453 F 190 Pl 331 li 208 l 339 l 203 PBr 272 BBr 193 Br 276 Br 234 PI 184 BrI 175 I 216 I 234 II 151 = 614 N=N N N 945 =N 615 N= 607 N 891 N 631 = 745* = *799 in 2 Use bond energies to calculate H 0 rxn for the combustion of methane H4(g) + 2 2(g) 2(g) + 2 H2(g) alculate H 0 rxn for the chlorination of methane to form chloroform H4 + 3 l2 Hl3 + 3 Hl We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 11 of 14

12 Between the extremes Electronegativity and Bond Polarity Extreme 1 non-polar covalent bonding Extreme 2 ionic bonding Between the extremes a polar covalent bond We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 12 of 14

13 Electronegativity the ability of an atom in a covalent bond to attract the shared electron pair Depicting Polar Bonds EN ranges for classifying the partial ionic character of bonds Exact range varies from textbook to textbook We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 13 of 14

14 oncept heck ompound A is a solid with a melting point of 125, and compound B is a gas at 25 and one atmosphere pressure. Based on these data, one would expect a. both compounds to be covalent. b. compound A to be ionic and compound B to be covalent c. compound A to be covalent and compound B to be ionic d. both compounds to be ionic oncept heck The electronegativity is 2.1 for H and 1.8 for Si. Based on these electronegativities, SiH4 would be expected to a. be ionic b. have non polar covalent bonds c. have polar covalent bonds with a partial negative charges on the H atoms d. have polar covalent bonds with a partial positive charges on the H atoms. Rank the following bonds in order of increasing polarity: H N, H, H The EN values are: N = 3.0, H = 2.1; = 3.5; = 2.5 We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 14 of 14