COVALENT BONDS OCTET RULE ELECTRONEGATIVITY 1. Bonds formed by sharing electrons between atoms 2. Group of atoms held together by covalent bond, called molecule OCTET RULE 1. 8 electrons (4 pair) around atom -- Hydrogen 2 e-’s or 1 pair 2. Occurs mostly with Main Group Elements (IA-VIIIA) 3. Results in Noble Gas electron configuration for each atom ELECTRONEGATIVITY The ability of an atom to attract pair of electrons in covalent bond F, fluorine, most electronegative element P.table: most upper right of table least lower left of table use to show partial “+” charge on less electroneg. atom use to show partial “-” charge on more electroneg. atom

BONDING PATTERNS/REQUIREMENTS pg. 111 Hydrogen (1) Nitrogen (3) Oxygen (2) Halogens (1) carbon (4) X = F, Cl, Br, I N .. : O .. C H X .. : N + Nitrogen Ion, N+, (4)

BOND GROUP EXCEPTIONS 3 Boron, B Aluminum, Al 4 Silicon, Si 3 Phosphorus, P also 5 2 Sulfur, S also 4 & 6 1 Chlorine, Cl Bromine, Br also 3 & 5 1 Iodine, I also 3, 5, & 7

1. Sum the total number of valence electrons from all atoms in subst. LEWIS STRUCTURES pg. 122 Helps in understanding bonding in cmpds/molecules STEPS 1. Sum the total number of valence electrons from all atoms in subst. 2. Identify central atom. Write chem.symbols of atoms to show which atoms are attached to each other 3. Place 2 e-’s to show a bond between each atom 4. Complete the octet rule for each atom 5. If not enough e-’s to give central atom octet, try multiple bonds

Draw Lewis structure for phosphorus trichloride, PCl3 1. Total valence e-’s P: 1s22s2p63s2p3: 5 Cl: 1s22s2p63s2p5: 7 * 3 = 21 total = 5 + 21 = 26 2. Central atom: P Attached: 3 Cl’s 3. Place 2 e-’s to show bonds Cl:P:Cl Cl .. 26 - 6 = 20 e-’s left to account for .. : 20 - 20 = 0 4. Complete octet :Cl:P:Cl: :Cl .. 5. No e-’s left, no multiple bonds Final step, replace bonding pairs with line to represent the bond(s) between .. :Cl P Cl: :Cl:

P GEOMETRY AB3E Pyramidal :Cl P Cl: :Cl: 3-D DRAWING Cl 4 possible bonding sites, tetrahedral in this case; 3 bonds, 1 lone pair GEOMETRY AB3E Pyramidal .. :Cl P Cl: :Cl: 3-D DRAWING P .. Cl :

P POLARITY Cl more electronegative than P :Cl P Cl: :Cl: .. :Cl P Cl: :Cl: Cl: 3.0 P: 2.1 .. :Cl P Cl: :Cl: 3.0 – 2.1 = 0.9 POLAR BOND OVERALL POLARITY OF MOLECULE P .. Cl :

POLARITY pg. 130 H F H F Nonpolar: equal sharing of e- pair in bond occurs when electronegativity value is less than 0.5 all diatomics are nonpolar Polar: unequal sharing e- pair in bond occurs when electronegativity diff. between 0.5 & 2.0 Determine electronegativity value, show δ partial charges, and overall polarity in the molecule, HF H F 2.1 4.0 4.0 - 2.1 = 1.9 polar covalent H F

C HCN 10 – 8 = 2 H C N H C N H C N bonds: val. e-: 1 4 3 1 4 5 = 10 .. H C N .. bonds: val. e-: 1 4 3 1 4 5 = 10 .. H C N .. .. .. .. DOT LEWIS 3-D STRUCTURE STRUCTURE DRAWING RESONANCE STRUCTURE moleucle described as blend (composite) of 2+ Lewis structures CO3-2; carbonate ion 6 – 6 = 0 .. : 12 – 6 = 6 C O .. : .. C O .. bonds: val. e-: 4 2 4 6 (3) = 22 + 2e- = 24 .. : : 24 – 6 = 18 18 – 6 = 12

.. : C O -2 .. : C O : .. C O

GEOMETRY AROUND CENTRAL ATOM Pg. 123 Bonds Lone Pair Geometry Formula Bond 2 0 Linear AB2 1800 3 0 Planar Triangular AB3 1200 2 1 Angular (Bent) AB2E < 1200 4 0 Tetrahedral AB4 109.50 3 1 Pyramidal AB3E 1070 2 2 Bent AB2E2 1050 5 0 Trigonal Bipyramidal AB5 900, 1200 6 0 Octahedral AB6 900

Condensed: shows atom connections without showing bonds FORMULA TYPES Condensed: shows atom connections without showing bonds Molecular: shows how many of each diff. atom in molecule Structural: shows lines (bonds) between atoms to show connection of atoms Lewis: shows bonds & lone pair e- Condensed Structural Molecular Lewis C C C C C C OH H H3C O (CH3)2CHCH2COCH2CH2COOH C8H14O3 C C C C C C OH H H3C O : : : :

VSEPR Valence Shell Electron-Pair Repulsion 1. Method to predict molecular shape based upon electron charge around atoms 2. Assume electron cloud regions will repel and orient as far apart as possible from each other 3. States, “bonding electrons & lone electron pairs of an atom will adopt a spatial arrangement that minimizes electron-pair repulsion around that atom” MULTIPLE BONDS (between atoms) Single bond: 1pair electrons, total: 2 e- double bond: 2 pair electrons, total: 4 e- triple bond: 3 pair electrons, total: 6 e-

NAMING BINARY COVALENT MOLECULES 1. Use prefixes 1: mono 2: di 3: tri 4: tetra 5: penta 6: hexa 7: hepta 8: octa 9: nona 10: deca 2. 1st element: name of element, no prefix unless more than 1 for subscript 3. 2nd element: name, ending changed to-ide, always use prefix CO 2nd: oxygen, -ide ending only 1, prefix mono 1st: carbon; only 1, no prefix Carbon Monoxide

CO2 N2O P2Cl5 N2O4 Carbon Dioxide Dinitrogen Monoxide Diphosphorus Pentachloride Dinitrogen Tetroxide N2O4 Silicon Hexafluoride SiF6

CH4 CHCl3 BF3 CH2Br2 Methane Trichloromethane Boron Trifluoride Dibromomethane Diiodine Nonoxide I2O9

ION DIAGRAMS ClO2-1 or O2Cl-1 (chlorite ion) PO4-3(phosphate ion) total e- 7 + 12 + 1 = 20 5 + 24 + 3 = 32 central Cl P .. .. -1 .. -3 O Cl O .. .. O P O O

RESONANCE A molecule as a blend of diff structures as, green, blend primary colors blue & yellow Ozone, O3 .. .. O .. O .. .. SO3-2 (sulfite ion) .. O S .. O S .. O S