Name Date Period In Class Bonding Unit Homework Molecular Formulas and Lewis Structures Electronegativity: a measure of an atom’s tendency to attract shared electrons to itself in a molecule Molecular compound: compound composed of only nonmetals Covalent bond: a bond between two nonmetals in which electrons are shared by atoms Octet rule: atoms tend to be most stable when their valence sublevels are filled; 8 valence electrons How to draw Lewis structures for molecular (covalent) compounds. (Please fill in, the space below, the directions that were on the video guide). 1. 2. 3. 4. FC = valence electrons - # of bonds – lone electrons in other words, formal charge = valence – sticks – dots H 2.20 Li 0.98 Na 0.93 K 0.82 Rb 0.82 Cs 0.79 Fr 0.70 Be 1.57 Mg 1.31 Ca 1.00 Sr 0.95 Ba 0.89 Ra 0.90 B 2.04 Al 1.61 Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga 1.36 1.54 1.63 1.66 1.55 1.83 1.88 1.91 1.90 1.65 1.81 Y Zr Nb Mo Tc Ru Rb Pd Ag Cd In 1.22 1.33 1.60 2.16 1.90 2.20 2.28 2.20 1.93 1.69 1.78 La Hf Ta W Re Os Ir Pt Au Hg Tl 1.10 1.30 1.50 2.36 1.90 2.20 2.20 2.28 2.54 2.00 2.04 Ac 1.10 C 2.55 Si 1.90 Ge 2.01 Sn 1.96 Pb 2.33 N 3.04 P 2.19 As 2.18 Sb 2.05 Bi 2.02 O 3.44 S 2.58 Se 2.55 Te 2.10 Po 2.00 F 3.98 Cl 3.16 Br 2.96 I 2.66 At 2.20 Kr 3.0 Xe 2.6 Rn 2.4 On your own paper: 1. Draw Lewis structures that obey the octet rule for each of the following: a. HCN e. H2CO b. PH3 f. SeF2 c. CHCl3 g. O2 d. ammonium h. HBr 2. Which is the better structure of the 2 Lewis Dot diagrams in the following molecules? Show proof in available space! BCl3 BCl3 SO2 SO2 IF5 IF5 N2 N2 2 HCO2- HCO2- SO4-2 SO4-2 3. Draw Lewis structures for each of the following: a. POCl3, XeO4, phosphate, perchlorate b. NF3, phosphite, chlorate c. Chlorite, SCl2, PCl24. Draw Lewis structures for the following molecules or ions, which have central atoms that do not obey the octet rule: a. PF5 e. SF4 b. BeH2 f. XeF4 c. BH3 g. ClF5 d. Br3h. SF6 5. ClF3 and BrF3 are both used to fluorinate uranium to produce UF6 in the processing of nuclear fuel. Draw Lewis structures for ClF3 and BrF3. 6. Draw Lewis structures for the following: a. BF2Br b. SiO2 c. CF4 d. TeH2 e. f. g. h. 3 AlH3 CH3Cl BBr3 SCN- RESONANCE STRUCTURES A way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula. A molecule or ion with such delocalized electrons is represented by several contributing structures also called resonance structures. In other words, resonance structure is an alternate way of drawing a Lewis dot structure for a compound. 7. Draw the resonance structure for each molecule: a. ClO3- b. Nitrate c. O3 d. Carbonate 4 Molecular Geometry Guide: AXE Method Molecule Type Steric number Hybridiz a-tion AX2 2 AX2E1 KEY: A = Central Atom X = Surrounding Atom(s) E = # of lone pairs around central atom Electronic arrangement (w/ lone pairs) Shape name Bond angle sp Linear 180° 3 sp2 Bent 120° AX3 3 sp2 Trigonal Planar 120° AX2E2 4 sp3 Bent 109° AX3E1 4 sp3 Trigonal Pyramidal 109° AX4 4 sp3 Tetrahedral 109.° AX2E3 5 sp3d Linear 180° 5 Example s AX3E2 5 sp3d T-shaped 90° AX4E1 5 sp3d Seesaw 120° 90° AX5 5 sp3d Trigonal 90° Bipyramidal 120° AX4E2 6 sp3d2 Square Planar 90° AX5E1 6 sp3d2 Square Pyramidal 90° AX6 6 sp3d2 Octahedral 90° VSPER THEORY: The geometric arrangement of terminal atoms, or groups of atoms about a central atom in a covalent compound, or charged ion, is determined solely by the repulsions between electron pairs present in the valence shell of the central atom. In other words, because of electron repulsion atoms in a molecule or compound want to be as far from each other as possible. 6 Molecule BeH2 BH3 NO2־ CH4 NH3 H2 O PCl5 Lewis Structure # Atoms Attached # Lone Pairs Steric Number Hybridization Actual Shape Shape Name Bond Angles Molecule Lewis Structure # Atoms Attached # Lone Pairs Steric Number Hybridization SF4 ClF3 I3־ SF6 XeOF4 XeF4 8 Actual Shape Shape Name Bond Angles POLARITY Polar = difference in electronegativity between two bonded atoms Evaluate each bond individually. Use arrows to indicate where the charge is. Imagine you are the central atom. Will you move? BF3 BClF2 XeO4 NH3 PCl5 PCl4F Fun With Molecules! You have the following molecules: XeO3, BeCl2, XeF4, PCl5F-, NO3- A scientist gave these molecules pet names and left clues for his lab aids to identify them. Use the clues to figure out which name corresponds to each molecule. You might guess these molecules, but you’ll need more than the names to please this scientist. On a separate page, (i) Show the most stable structure (ii) Determine shape (iii) Determine molecular polarity (iv) Determine bond angles (v) Write the “name” of the molecules. “Billy” used to be nicknamed after the sea villain in “The Little Mermaid.” “Davey” has never been in charge, but he’s very willing to wait his turn in line. Though “Puck” can be negative and two-dimensional, he resonates well. “Sarah” is really noble at heart, but she’s just too square for my tastes. Don’t you think “Milo” looks like a tricycle? Hmm. Let’s take a pole or something.