Principles 1 Week 12

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Monday April 1, 2024 Day 50 Lewis Dot Structures
Textbook Readings : 9.7: Lewis Structures	Course Lectures 10.1 pdf Video Lewis Dot Structures
Objectives 1. Predict the center atom in a molecule and create a skeletal structure around it. 2. Determine total valence electrons for molecules and polyatomic ions. 3. Distribute valence electrons observant of duets, octets and exceptions to these rules. 4. Identify correct and incorrect Lewis dot structures.	10.1 Lewis Dot Structures
Homework Problems 54.1 Atoms with the lowest electronegativity are usually the center atom in a molecule. Use electronegativity values to determine which element occupies the center position in each of the following molecules or polyatomic ions: a. SiH₄ b. Br₂CO c. N₂O d. BrO^- e. NH₄⁺ f. C₂H₄ g. PF₅ h. XeF₄ 54.2 54.1 Continued: Determine the total number of valence electrons avilable you'll use to construct the Lewis structure. Show your work. 54.3 54.1 Continued: Determine the skeletal structure or framework for each species. Use a "-" to represent the single bonds that link the center atom to the outer atoms. For each, determine the remaining/unused valence electrons to be use in the next step. 54.4 54.1 Continued: Distribute the valence electrons around each atom in an attempt to satisfy with either a duet (hydrogen) or an octet. Be aware of exceptions like boron (6 electrons) and beryllium (4 electrons). 54.5 54.1 Continued: Distribute any remaining electrons around the centermost atom. If an atom is requires more electrons, convert lone pair into bonding electrons. Use brackets around polyatomic ions and indicate the ion's charge. 54.6 Determine the correct Lewis dot structures for each of the following: a. CO₂ b. H₂O c. H₃O⁺ d. H₂CO e. NO₂^- f. CO₃^-2 Click and drag the region below for correct answers 54.1 a. Si b. C c. N d. No Center....two atoms e. N f. C or C (two centers) g. P h. Xe 54.2 a. 8 valence electrons (v.e.) b. 24 v.e. c. 16 v.e. d. 14 v.e. (negative sign indicates one additional v.e. is present) e. 8 v.e. (positive sign indicates one less v.e. is present) f. 12 v.e. g. 40 v.e. h. 36 v.e. ...still have 4 v.e. left to place 54.3 Click here 54.4 Click here 54.5 Click here 54.6 You're on your own on these! :)

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Tuesday April 2, 2024 Day 51 Resonance and Formal Charge: Variations of Lewis Structures
Textbook Readings 9.8: Resonance and Formal Charge	Course Lectures 10.2 pdf Video Resonance Structures 10.3 pdf Video Formal Charges
10.2 Resonance Structures	10.3 Formal Charges
Objectives 1. Create different Lewis structures (Resonance structures) by moving lone pair electrons into multiple bonding situations while maintaining the octet rule. 2. Create Resonance Hybrid structures that represent multple resonance structures. 3. Correctly calculate formal charges on molecular atoms. 4. Use formal charges to correctly identify the most likely Lewis structure from the various possibilities.
Homework Problems 55. 1. What are the formal charges for all atoms in the H - C ≡ N - O molecule? The "O" atom also has 6 lone pair electrons. 55.2 For the following three SCN resonance structures, determine the formal charges of all atoms. Use your formal charge information to determine which structure contributes most to the overall SCN structure. (Source) 55.3 Draw all of the possible resonance structures for the following ions or molecules. a. Nitrate ion: NO₃^-1 b . Formate ion CHO₂^-1 c. Ozone O₃ d. Carbonate ion CO₃^2- 55.4 Draw the three Lewis structures for OCN^-1 and identify the structure which is most correct. Assume the skeletal structure is the atomic order in the formula provided. Click and drag below for answers: 55.1 FC_H = 1 - ½ (2) - 0 LP = 0 FC_C = 4 - ½ (4) - 0 LP = 0 FC_N = 5 - ½ (4) - 0 LP = +1 FC_O = 6 - ½ (2) - 6 LP = -1 55.2 Structure "a" FC_S = -1 FC_C =0 FC_N = 0 Structure "b" FC_S = 0 FC_C =0 FC_N = -1 Structure "c" FC_S = +1 FC_C =0 FC_N = -2 Structure "c" contributes least since it has FC's furthest from zero. Structure "b" contributes the most since the negative formal charge is on the higher E_nelement 55.3 Use this "source" link 55.4 You're on your own! :)

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Wednesday April 3, 2024 Day 52 Lewis Structures and Expanded Octets
Textbook Readings 9.9: Exceptions to the Octet Rule	Course Lectures 10.1 pdf Video Lewis Dot Structures
Objectives 1. Memorize the more common octet rule exceptions and their unique electron requirements. 2. Define the term "expanded octet" and explain how & why not all elements are capable of an expanded octet. 3. Correctly draw Lewis structures for "odd electron" molecules	Exceptions to the Octet Rule

Homework Problems 56.1 Draw the Lewis structures for BeCl₂, BH₃, SF₄, I₃^-1 , PF₆ ^-1 and BrF₅ 56.2 The NO₂ molecule is an odd electron species. Draw the two resonance structures for the NO₂ molecule and include all formal charges. Click and drag the region below for correct answers 56.1 Click on links for YouTube solutions BeCl₂, BH₃, SF₄, I₃^-1 , PF₆ ^-1 and BrF₅ 56.2 Click here for solutions

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Thursday April 4, 2024 Day 53 Bond Energy and Bond Length Determinations
Textbook Readings 9.10: Bond Energies and Bond Lengths	Course Lectures 9.5 pdf Video Introduction to Bond Energy 9.6 pdf Video Bond Energy Example 9.7 pdf Video Bond Lengths and Energies 9.8 pdf Video Fuels
Bond Energy and Bond Length	Bond Energy Calculations
Objectives 1. Know what high and low bond energies mean in terms of bond strength. 2. Describe how bond length generally relates to bond length. 3. Calculate ΔH_rxnusing the balanced chemical reaction and tabulated bond energies. (FYI: bond energy tables are always provided on exams.)
Homework problems. 57.1 The figure at right breaks down the reaction of hydrogen and oxygen gas to form water. When using bond energies to determine the ΔH_rxn, you calculate the energy required to break all bonds and subtract the energy required to make all bonds.
Given the bond energies available here, calculate the break bond total, make bond total, and the ΔH_rxn. This is a combustion reaction and is known to be exothermic. Does your ΔH value support this fact?
57.2 Use the bond energies here to determine the ΔH for the following reactions. a. C₄H_{10 (g)} + 13/2 O_{2 (g)} → 4CO_2(g) + 5H₂O_(g) b. N_2(g) + 3 H_{2 (g)} → 2NH_3(g) c. CH_4(g) + 3 Cl_2(g) → CHCl_3(g) + 3HCl_(g) 57.3 Use the bond energies available here to determine the strongest and weakest bonds. 57.4 Generally, short bonds are stronger than long bonds. Is this the case for your answers to 57.3? 57.5 Compare the C-H, C-F and C-Cl bonds and determine if they follow the trend that shorter bonds are stronger bonds. 57.6 Identify the longest bond in the table and compare its bond length to others. Do your observations support the trend that long bonds are weak? Click and drag below for answers. 57.1 -509 kJ/mol 57.2 a. -2674 kJ/mol b. - 109 kJ/mol c. -342 kJ/mol 57.3 Strongest: C ≡ O E = 1072 kJ/mol Weakest: O - O E = 146 kJ/mol 57.4 C ≡ O E = 1072 kJ/mol Bond Length = 113 pm O - O E= 146 kJ/mol Bond Length = 148 pm Yes. In this case, the shorter bond is the stronger bond with higher bond energy. 57.5 In this case, the strongest bond is the C-F bond. However, the shortest bond is the C-H bond. This is quite typical as bond energies & lengths between different atoms can exhibit exceptions to general trends. 57.6 Longest bond: I-I 267 pm. This bond's energy is 149 kJ/mol ... not the weakest bond but very close (O-O 146 kJ/mol) This example does generally support the idea that long bonds are weak.

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Friday April 5, 2024 Day 54 Valence Shell Electron Pair Repulsion (VSEPR Theory)
Textbook Readings 10.2: VSEPR Theory and the five fundemental shapes.	Course Lectures 10.4 pdf Video VSEPR Part I
Objectives 1. Recognize exceptions to the octet rule and correctly draw Lewis structures for them. 2. Correctly determine the number of bonding regions in a Lewis structure (focusing on the centermost atom). 3. Identify the electronic geometry name from the number of bonding regions for molecules having NO lone pair. 4. Draw molecular pictures using bond "wedges" and dotted lines to add perspective. 5. Correctly identify and label all bond angles.	10.4 VSEPR Part I
Homework Problems 59.1 For each of the following 5 molecules.... i. Draw the Lewis Structure ii. Determine the number of bonding regions and the electronic geometry name. iii. Draw a molecular picture and identify all bond angles. a. BeCl₂ b. CCl₄ c. BF₃ d. PF₆^- e. PBr₅ Click and drag below for answers Click HERE for answer "a" Click HERE for answer "b" Click HERE for answer "c" Click HERE for answer "d" Click HERE for answer "e"

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