Slide 1 / 36 Slide 2 / 36 New Jersey Center for Teaching and Learning AP Chemistry Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written Unit 4: Presentation A permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to Covalent Bonding make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org www.njctl.org Slide 3 / 36 Slide 4 / 36 What is a chemical bond? Covalent Bonding A chemical bond results from the coulombic attraction of one atom or ion for another. When the N 2 bond forms, enormous Covalent Bond(F 2 ) amounts of energy Ionic Bond (NaCl) are released, making Nitrogen e- widely used in e- 9 p+ 9 p+ Cl- Na + explosives. Nuclei are attracted to Charged ions are attracted to shared pairs of electrons each other between nuclei. Slide 5 / 36 Slide 6 / 36 Why do atoms form bonds? Where do we find chemical bonds? Coulombic attractions develop both between atoms within Atoms form bonds because it lowers their potential energy. Bond molecules but also between neighboring molecules. formation is exothermic as energy will be released. Intramolecular Attractions Repulsions predominate Intermolecular Attractions Nuclei are too far apart (within molecules) (between molecules) to be attracted to each Distance between nuclei others electrons Hydrogen Ionic Bonds Potential bonding between Energy (kJ/mol) neighboring Attractions developing O water molecules Covalent Bonds H H Coulombic attractions maximized, repulsions minimized
Slide 7 / 36 Slide 8 / 36 Intramolecular Attractions 1 When atoms form bonds, energy is released. How ionic or covalent a bond is depends on the electronegativity True difference between the atoms involved. False Electronegativity Difference 0 0.4 1.7 3 non-polar polar covalent ionic covalent The more similar the electronegativities, the more likely the electrons will be shared. This becomes less likely as the electronegativity difference becomes great and the bond takes on a more ionic character. Slide 8 (Answer) / 36 Slide 9 / 36 2 Which of the following processes would NOT be 1 When atoms form bonds, energy is released. exothermic? True A H + H --> H 2 False B Na + (g) + Cl - (g) --> NaCl(s) Answer C MgF 2 (s) --> Mg 2+ (g) + 2F - (g) True D A and B E A and C [This object is a pull tab] Slide 9 (Answer) / 36 Slide 10 / 36 2 Which of the following processes would NOT be 3 Which of the following is TRUE regarding bond formation? exothermic? A H + H --> H 2 A Bonding results from nuclei - nuclei coulombic attractions B Na + (g) + Cl - (g) --> NaCl(s) B Bonding results from nuclei - electron coulombic C MgF 2 (s) --> Mg 2+ (g) + 2F - (g) attractions Answer C D A and B C The potential energy increases as repulsions become significant E A and C D A and B [This object is a pull tab] E B and C
Slide 10 (Answer) / 36 Slide 11 / 36 3 Which of the following is TRUE regarding bond formation? 4 Which of the following involves the breaking of intermolecular forces? A Bonding results from nuclei - nuclei coulombic A 2H 2 O(l) --> 2H 2 (g) + O 2 (g) attractions B C(s) + 2H 2 (g) --> CH 4 (g) B Bonding results from nuclei - electron coulombic attractions Answer E C I 2 (s) --> I 2 (g) C The potential energy increases as repulsions D CO 2 (g) --> C(s) + O 2 (g) become significant E None of these D A and B [This object is a pull tab] E B and C Slide 11 (Answer) / 36 Slide 12 / 36 4 Which of the following involves the breaking of 5 As the electronegativity difference between atoms intermolecular forces? becomes greater, the bond takes on a more covalent character. A 2H 2 O(l) --> 2H 2 (g) + O 2 (g) True B C(s) + 2H 2 (g) --> CH 4 (g) False Answer C I 2 (s) --> I 2 (g) C D CO 2 (g) --> C(s) + O 2 (g) E None of these [This object is a pull tab] Slide 12 (Answer) / 36 Slide 13 / 36 5 As the electronegativity difference between atoms 6 Which of the following bonds is most ionic in character? becomes greater, the bond takes on a more covalent character. A Al-O True B Si-O False C Li-O Answer False D H-O E Rb-O [This object is a pull tab]
Slide 13 (Answer) / 36 Slide 14 / 36 6 Which of the following bonds is most ionic in character? 7 Which of the following bonds would be most covalent in character? A Al-O A C-H B Si-O B C-S Answer C Li-O E C C-O D H-O D C-F E Rb-O E C-N [This object is a pull tab] Slide 14 (Answer) / 36 Slide 15 / 36 Ionic Bond Formation 7 Which of the following bonds would be most covalent in character? Ionic bonding occurs in a series of steps, most of which require energy but occur because they are coupled to the highly exothermic formation of the bond. A C-H Formation of LiF(s) from it's elements in their standard state. B C-S Li(s) + 1/2F 2 (g) --> LiF(s) Answer C C-O B Event Reaction Energy Change Sublimation of Li(s) Li(s) --> Li(g) +180 kJ/mol D C-F Ionization of Li(g) Li(g) --> Li+(g) + e- +520 kJ/mol Breaking of existing F-F bond 1/2F 2 (g) --> F(g) +157 kJ/mol E C-N Ionization of F(g) F(g) + e- --> F-(g) -328 kJ/mol Bond formation Li+(g) + F-(g) --> LiF(s) -1036 kJ/mol [This object is a pull tab] Overall energy change = -505 kJ/mol Highly exothermic Slide 16 / 36 Slide 17 / 36 Ionic Bond Formation Lattice Energy The magnitude of the lattice energy is influenced by the charge The thermochemical steps for ionic bond formation are often and size of the ions involved. summarized in a Born-Haber Cycle Diagram The higher the charges, Substance Charges Lattice Energy the greater the coulombic NaF(s) +1 and -1 -923 kJ/mol attraction and the higher The energy MgO(s) +2 and -2 -3791 kJ/mol the lattice energy. released when the gaseous ions The smaller the ionic combine is known Substance Ionic radii Lattice Energy as the Lattice radii, the greater the NaF(s) F- = 117 pm -923 kJ/mol Energy coulombic attraction and NaCl(s) Cl- = 167 pm -786 kJ/mol the higher the lattice energy Hf represents the overall energy change of the process.
Slide 18 / 36 Slide 18 (Answer) / 36 8 Which of the following would have the highest 8 Which of the following would have the highest lattice energy? lattice energy? A BeO A BeO B MgS B MgS C MgCl 2 C MgCl 2 Answer A D MgI 2 D MgI 2 E NaF E NaF [This object is a pull tab] Slide 19 / 36 Slide 19 (Answer) / 36 9 Rank the following from lowest to highest lattice energy. 9 Rank the following from lowest to highest lattice energy. A I < II < III A I < II < III B I < III < II B I < III < II I. NaBr I. NaBr II. LiBr II. LiBr C II < III < I C II < III < I Answer E III. LiF III. LiF D II < I < III D II < I < III E III < II < I E III < II < I [This object is a pull tab] Slide 20 / 36 Slide 20 (Answer) / 36 10 Which of the following BEST explains why the lattice 10 Which of the following BEST explains why the lattice energy of CaS is lower than that of MgO? energy of CaS is lower than that of MgO? A CaO has lower ionic charges than MgO A CaO has lower ionic charges than MgO B The calcium ion has more shielding than the B The calcium ion has more shielding than the magnesium ion magnesium ion Answer B C The calcium ion has a smaller nuclear charge than C The calcium ion has a smaller nuclear charge than magnesium ion magnesium ion D CaO has higher ionic charges than MgO D CaO has higher ionic charges than MgO [This object is a pull tab] E None of these E None of these
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