Basic Concepts of Chemical Bonding Test (Answer Key Part 4)

57) Using the table of bond dissociation energies, the ΔH for the reverse of following gas-phase reaction is ________ kJ. A) +57 B) +291 C) 2017 D) -57 E) -291 Answer: A 58) Using the table of bond dissociation energies, the ΔH for the following reaction is ________ kJ. 2HCl (g) + F2 (g) → 2HF (g) + Cl2 (g) A) -359 B) -223 C) 359 D) 223 E) 208 Answer: A 8.3 Algorithmic Questions 1) There are ________ paired and ________ unpaired electrons in the Lewis symbol for a fluorine atom. A) 4, 2 B) 4, 1 C) 6, 1 D) 0, 5 E) 2, 5 Answer: C 2) The ________ ion has a noble gas electron configuration. A) Be2+ B) Li2+ C) Li D) Mg2E) Al2+ Answer: A 3) The ________ ion has a noble gas electron configuration. A) ClB) F2C) F D) S2+ E) OAnswer: A 4) The ________ ion has eight valence electrons. A) Sc3+ B) Ti3+ C) V3+ D) Cr3+ E) Mn3+ Answer: A 5) There are ________ unpaired electrons in the Lewis symbol for an oxygen atom . A) 0 B) 1 C) 2 D) 4 E) 3 Answer: C 6) What is the principal quantum number of the last shell for the element barium? A) 5 B) 4 C) 3 D) 6 E) 2 Answer: D 7) The oxide of which of the following metals should have the greatest lattice energy? A) calcium B) strontium C) magnesium D) beryllium E) barium Answer: D 8) The ________ ion is represented by the electron configuration [Ar]3d2. A) Cr4+ B) V4+ C) Ti4+ D) Mn4+ E) Sc4+ Answer: A 9) Which of the following species does the noble gas electron configuration [Kr]4d10 represent? A) Cd B) Cd+ C) Ag+ D) Ag2+ E) Sr2+ 10) Which of the following noble gas electron configurations represents the Ru+ cation? A) [Kr]5s24d5 B) [Kr]5s24d7 C) [Kr]4d5 D) [Ar]4s13d6 E) [Kr]5s14d6 Answer: E 11) Ni2+ ions are represented by the electron configuration ________. A) [Ar]3d8 B) [Ar]3d10 C) [Ar]3d6 D) [Ar]4s23d6 E) [Kr]4d8 Answer: A 12) How many single covalent bonds must a chlorine atom form to have a complete octet in its valence shell? A) 0 B) 1 C) 2 D) 3 E) 4 Answer: B 13) The most electronegative atom of the ones listed below is ________. A) B B) Al C) Ga D) In E) Tl Answer: A 14) Of the atoms below, ________ is the most electronegative. A) Ba B) Sr C) Ca D) Mg E) Be Answer: E 15) Of the atoms below, ________ is the most electronegative. A) C B) Si C) Ge D) B E) Al Answer: A 16) Of the atoms below, ________ is the least electronegative. A) B B) F C) C D) N E) O Answer: A 17) Of the bonds below, ________ is the least polar. A) C-O B) N-O C) C-F D) S-O E) K-Br Answer: B 18) Which two bonds are most similar in polarity? A) O-F and Cl-F B) B-F and Cl-F C) Al-Cl and I-Br D) I-Br and Si-Cl E) C-Cl and Be-Cl Answer: A 19) There are ________ valence electrons in the Lewis structure of CH3Cl. A) 14 B) 16 C) 18 D) 20 E) 22 Answer: A 20) How many valence electrons are in the Lewis structure of CH3OCH3.? A) 16 B) 18 C) 20 D) 24 E) 22 Answer: C 21) In the Lewis symbol for a nitrogen atom, there are ________ paired and ________ unpaired electrons. A) two, three B) one, three C) three, two D) zero, five E) two, two Answer: A 22) The oxidation number of phosphorus in PF5 is ________. A) +5 B) +3 C) +1 D) -5 E) 0 Answer: A 23) The central atom in ________ violates the octet rule. A) PF5 B) SF2 C) Cl2 D) Br2CO E) FCN Answer: A 24) Of the following, ________ cannot accommodate more than an octet of electrons. A) Ni B) Sc C) Be D) Os E) Sb Answer: C 25) How many covalent bonds are in the Lewis Structure of CH3CHCl2.? A) 6 B) 8 C) 7 D) 5 E) 4 Answer: C Short Answer Questions 1) The electron configuration that corresponds to the Lewis symbol, : : is ________. Answer: [Ne]3s23p6 2) Write the balanced chemical equation for the reaction for which △H°rxn is the lattice energy for sodium chloride. Answer: NaCl (s) → Na+ (g) + Cl- (g) 3) Using the noble gas shorthand notation, write the electron configuration for Fe2+. Answer: [Ar]3d6 4) Give the electron configuration of Zn2+. Answer: [Ar]3d10 5) Which halogen, bromine or iodine, will form the more polar bond with phosphorus?Answer: bromine 6) Draw the Lewis structure of ICl2+. Answer: 7) If more than one Lewis structure can be drawn then the molecule or ion is said to have ________ forms. Answer: resonance 8) How many resonance forms exist for benzene? Answer: two 9) If the bonds in the reactants of a reaction are weaker than the bonds in the product, the reaction is ________. Answer: exothermic 10) Which two elements in period 2 form compounds that can violate the octet rule? Answer: boron and beryllium 11) Polyatomic ions with an even number of electrons will follow the ________ rule. Answer: octet 12) The strength of a ________ bond is measured by its bond enthalpy. Answer: covalent 13) An exothermic reaction should have ________ chemical bonds and decompose to a molecule with ________ bonds. Answer: weak, strong 14) Calculate the bond energy of C—F given that the heat of atomization of CHFClBr is 1502 kJ/mol, and that the bond energies of C—H, C—Br, and C—Cl are 413, 276, and 328 kJ/mol, respectively. Answer: ΔHatomization = [D(C—H) + D(C—F) + D(C—Cl) + D(C—Br)] D(C—F) = ΔHatomization - [D(C—H) + D(C—Cl) + D(C—Br)] = [1502 - (413 + 276 + 328)] kJ/mol = 485 kJ/mol 15) The reaction below is used to produce methanol: CO (g) + 2H2 (g) → CH3OH (l) △H rxn = -128 kJ (a) Calculate the C—H bond energy given the following data: (b) The tabulated value of the (C-H) bond energy is 413 kJ/mol. Explain why there is a difference between the number you have calculated in (a) and the tabulated value. Answer: (a) △Hrxn = D(C≡O) + 2 D(H-H) - [3 D(C-H) + D(C-O) + D(O-H)] 3 D(C-H) = -△Hrxn + D(C≡O) + 2 D(H-H) - D(C-O) - D(O-H) D(C-H) = (128 + 1072 + 2(436) - 358 - 463)/3 = 417 D(C-H) = 417 kJ/mol (b) Tabulated values, like those in Table 8.4, are averaged from many bond energies measured for C—H bonds in many different molecules. 16) From the information given below, calculate the heat of combustion of methane. Start by writing the balanced equation. Answer: CH4 + 2O2 → CO2 + 2H2O ΔHcombustion = (4 mol C—H)(DC—H) + (2 mol O O)(DO O) - [(2 mol C O)(DC O) - (4 mol O—H)(DO—H)] = [(4 × 413 + 2 × 495) - (2 × 799 + 4 × 463)] kJ ΔHcombustion = -808 kJ True/False Questions 1) Atoms surrounded by eight valence electrons tend to lose electrons. Answer: FALSE 2) The greater the lattice energy, the greater the charges on the participatory ions and the smaller their radii. Answer: TRUE 3) Most transition metals do not form ions with a noble gas configuration. Answer: TRUE 4) When a metal gains an electron, the process is endothermic. Answer: FALSE 5) Electron affinity is a measure of how strongly an atom can attract additional electrons. Answer: TRUE 6) As electronegativity difference increases, bond length will decrease. Answer: TRUE 7) In some molecules and polyatomic ions, the sum of the valence electrons is odd and as a result the octet rule fails. Answer: TRUE 8) A positive change in bond enthalpy is required to break a bond. Answer: TRUE