Chapter 12. Chemical Bonding Key

CHAPTER 12: CHEMICAL BONDING KEY 12.2 IONIC BOND Example: Draw the electron-dot symbols representing the following reactions: sodium atom + chlorine atom form ions to produce sodium chloride Na 12.3 + Cl → Na+ [ Cl ]- COVALENT BOND Ex: Use electron dot formulas to represent the reaction described. hydrogen atom H 12.4 + + chlorine atom Cl → → HCl molecule H Cl ELECTRON DOT FORMULAS OF MOLECULES Example: Draw the Electron dot formula for each of the following molecules: a. H2S SO3 c. Valence e- = 2x1 + 6 = 8 eelectron pairs = 8/2 = 4 pairs H Valence e- = 6 + 3x6 = 24 eelectron pairs = 24/2 = 12 pairs S O S H O CH2Br2 b. O Valence e- = 4 + 2x1 + 2x7 = 20 e- electron pairs = 20/2 = 10 pairs d. HCN Valence e- = 1+ 4 + 5 = 10 e- electron pairs = 10/2 = 5 pairs H C H Br H C N Br 12.4 ELECTRON DOT FORMULAS OF POLYATOMIC IONS Example: Draw the Electron dot formula for each of the following polyatomic ions: a. NH4+ Valence e- = 5 + 4x1 – 1 = 8 eelectron pairs = 8/2 = 4 pairs c. PO4–3 Valence e- = 5 + 4x6 + 3 = 32 eelectron pairs = 32/2 = 16 pairs 1 of 5 H N H O + P O H H -3 O O b. NO3– d. CO32– Valence e- = 5 + 3x6 + 1 = 24 eelectron pairs = 24/2 = 12 pairs Valence e- = 4 + 3x6 + 2 = 24 eelectron pairs = 24/2 = 12 pairs O N 2- O O O 12.9 C O O SHAPES OF MOLECULES Ex. Give the electron dot formula, shape, and bond angles for CO2 Valence e- = 4 + 2x6 = 16 eelectron pairs = 16/2 = 8 pairs C O AB2 O shape: linear angles: 180° Ex. Give the electron dot formula, shape, and bond angles for CH2O Valence e- = 4 + 2x1 + 6 = 12 e- electron pairs = 12/2 = 6 pairs H C H O AB3 shape: trigonal planar angles: 120° Ex. Give the Electron dot formula, shape, and bond angles for CH4. Valence e- = 4 + 4x1 = 8 e- electron pairs = 8/2 = 4 pairs H H C H AB4 Tetrahedral angles: 109.5° H MOLECULES WHERE CENTRAL ATOM HAS ONE OR MORE LONE PAIRS AB2E: bent ⇒ central atom is bonded to two outer atoms (B) and has a lone pair of electrons (E) 2 of 5 Ex. Give the electron dot formula, shape, and bond angles for SO2. Valence e- = 6 + 2x6 = 18 eS O electron pairs = 18/2 = 9 pairs AB2E O shape: bent angles: <120° AB3E: trigonal pyramid ⇒ central atom is bonded to two outer atoms (B) and has a lone pair of electrons (E) Ex. Give the electron dot formula, shape, and bond angles for NH3. Valence e- = 5 + 3x1 = 8 eH N H electron pairs = 8/2 = 4 pairs AB3E H shape: trigonal pyramid angles: <109.5° AB2E2: bent ⇒ central atom is bonded to two outer atoms (B) and has 2 lone pairs of electrons (E) Ex. Give the electron dot formula, shape, and bond angles for H2O. Valence e- = 6 + 2x1 = 8 eO H electron pairs = 8/2 = 4 pairs AB2E2 H shape: bent angles: <109.5° REFER TO TABLE OF MOLECULAR SHAPES AND BOND ANGLES TO ANSWER THE FOLLOWING Example For the following molecules or ions(where the central atom is underlined): i. Draw the Electron dot formula. ii. Determine the shape of the molecule. iii. Determine the approximate bond angles. a. CH2F2 b. OF2 Electron dot formula Electron dot formula Valence e- = 4 + 2x1 + 2x7 = 20 e- Valence e- = 6 + 2x7 = 20 e- electron pairs = 20/2 = 10 pairs electron pairs = 20/2 = 10 pairs 3 of 5 H H C F O AB4 F F AB2E2 F ii. shape of CH2F2: tetrahedral iii. bond angles in CH2F2: 109.5° ii. shape of OF2: bent iii. bond angles in OF2: <109.5° C. phosphite ion, PO3–3 Electron dot formula Valence e- = 5 + 3x6 + 3 = 26 eO P O electron pairs = 26/2 = 13 pairs -3 O ii. shape of PO3–3: trigonal pyramid iii. bond angles in PO3–3: <109.5° 12.6 POLAR COVALENT BONDS Example: For each of the bonds below: i. Use delta notation (δ and δ–) to indicate which atom is more electronegative, and ii. Use an arrow to point from the less electronegative atom to the more electronegative atom. δ+ δ− δ+ δ− δ+ δ− C-Cl N—O H—O Example: Identify the type of bond described for each of the following: A. ionic bond: metal-nonmetal C. polar covalent: 2 different nonmetals B. metallic bond: metal D. nonpolar covalent: 2 same nonmetals C i. The C–O bonds in CO2. D iv. The C–C bonds in C3H8 D ii. The bonds in F2. B v. The bonds in Ba. A iii. The bonds in K2O. C vi. The bonds in H2O. 4 of 5 12.9 SHAPES OF MOLECULES A molecule with polar bonds is polar if either of the following applies: 1) the central atom has one or more lone pair(s) of electrons, or 2) the atoms bonded to the central atom are not identical Ex. 1: Determine whether the following molecules are polar or nonpolar: CO2: nonpolar - no lone pairs on C and same outer atoms C O H2O: polar – O (the central atom) has 2 lone pairs of eO O H H SO3 nonpolar – no lone pairs on S and same outer atoms O S O O Ex. 2: Determine whether the following molecules are polar or nonpolar: H CCl4 nonpolar - outer atoms are the same and no lone pairs on central atom CHCl3 polar – outer atoms are different 5 of 5