Principles 1 Week 11

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Monday March 25, 2024 Day 45 Periodic Trends: Electron Affinity
Textbook Reading 8.8: Electron Affinities and Metallic Character 8.9: Examples of Periodic Chemical Behavior	Course Lectures 8.8. pdf Video Atomic Trends & Electron Affinity 8.9. pdf Video Atomic Trends, Ionic Size & Magentism
Electron Gain Enthalpy / Electron Affinity	Atomic Trends & Electron Affinity
Objectives 1. Know what exothermic and endothermic electron affinity values mean. 2. Write electron affinity equations. 3. Describe and explain how electron affinity values change throughout the periodic table. 4. Describe how the formation of 1/2 and full orbitals affect electron affinity values. 5. Predict metallic character throughout the periodic table.	CHEMISTRY 101: Electron affinity and metallic character
Homework Problems 49.1 Write the electron affinity equations and electron configurations for reactants and products for each of the following elements. The first one is done for you. a. Sodium: [Ne] 3s¹ Na + 1 e^- → Na^- [Ne] 3s² b. Potassium: c. Nitrogen: d. Oxygen: e. Fluorine: f. Carbon: g. Neon: 49.2 Sodium and potassium's electron affinities are -52.9 kj/mol and -48.4 kJ/mol respectively. Which element is more welcoming (exothermic) of an additional electron and why? 49.3 Fluorine and neon's electron affinities are -328.2 kJ/mol and + 25 kJ/mol respectively. Which element is more welcoming (exothermic) of an additional electron and why? 49.4 The general trend on the periodic table is for electron affinities to become more negative in going from left to right (and from bottom to top). As an example of this, consider the following elements and their electronegativity values: Carbon: E_a = -121.8 kJ/mol Nitrogen: E_a = +10 kJ/mol Oxygen: E_a = -141.0 kJ/mol a. Do carbon and oxygen E_a values confirm the general trend? b. Why does nitrogen not follow the trend as it has a positive E_a value but is to right of carbon? 49.5 Explain why cobalt's Ea value (-64 kJ/mol) is less negative than nickel's (-111.7 kJ/mol) 49.6 Which of the noble gases would would in theory have the largest, positive Ea value? 49.7 In 49.3 and 49.6 we mention noble gases and consider why their E_a values are positive values. Zinc isn't a noble gas and yet it's E_a value is positive. Why? 49.8 Which of the following would be considered most "metalic?" Gold Silver Zinc Tin Copper Platinum Click and drag the region below for correct answers 49.1 a. Sodium: [Ne] 3s¹ Na + 1 e^- → Na^- [Ne] 3s² b. Potassium: [Ar] 4s¹ K + 1 e^- → K^- [Ar] 4s² c. Nitrogen: [He] 2s² 2p³ N + 1 e^- → N ^- [He] 2s² 2p⁴ d. Oxygen: [He] 2s² 2p⁴ O + 1 e^- → O ^- [He] 2s² 2p⁵ e. Fluorine: [He] 2s² 2p⁵ F + 1 e^- → F ^- [He] 2s² 2p⁶ f. Carbon: [He] 2s² 2p² C + 1 e^- → C ^- [He] 2s² 2p³ g. Neon: [Ne] Ne + 1 e^- → Ne ^- [Ne] 3s¹ 49.2 Sodium is more receptive to an additional electron since its E_a value is more negative and therefore more exothermic. The reason is that the added electron is closer to the nucleus for the smaller sodium atom and therefore more energy is released when an electron is added. 49.3 Fluorine has the more negative E_a value and is therefore more welcoming of an extra electron. When an extra electron is added to the fluorine atom, the 2p orbital is full and the F- ion has a noble gas electron configuration! However, an extra electron ruins neon's noble gas electron configuration and that's why it takes energy to add an electron to a neon atom. 49.4 a. Yes. Carbon and oxygen follow the trend that Ea values should become more negative from left to right on the periodic table. This is because the oxygen atom is smaller and an extra electron can get closer to the nucleus. b. Nitrogen breaks the trend being positioned between carbon and oxygen but having a positive E_a value. The reason is that the neutral nitrogen atom has a low-energy half filled 2p orbital (2p³) to begin with. Adding another electron creates a partially filled 2p⁴ situation which isn't prefered and therefore requires energy to make happen. 49.5 Nickel has a more exothermic E_a value than cobalt since the nickel atom is smaller than the cobalt atom. This means an electron added to a nickel atom gets closer to the nucleus and is therefore at lower energy. 49.6 All noble gases have positive E_a values which is to say, none of them really want an extra electron. However, if forced to, the noble gas atom that would be most welcoming to an extra electron (E_a value closest to zero) would be the smallest and that would be helium. 49.7 The zinc electron configuration is [Ar] 4s² 3d¹⁰. where both the 4s and 3d orbitals are completely full. Although it's not a noble gas, the neutral Zn configuration has full orbitals and this gives the atom low energy and stability. Furthermore, another electron would create a partially full 4 p electron that adds no stability 49.8 Elements on the periodic table are considered more metalic moving down a group and left in a period. Platinum would be the most metalic of those listed.

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Tuesday March 26, 2024 Day 46 Survey of Bonding: Ionic, Covalent, Metallic Atomic Lewis Dot Structures
Textbook Readings 9.2: Types of Chemical Bonds 9.3: Representing Valance Electrons with Dots	Course Lectures
Chemical Bonding - Ionic vs. Covalent Bonds	GCSE Chemistry - Metallic Bonding
Objectives 1. Describe the process of electron transfer and how it leads to the formation of cations and anions. 2. Explain how electrostatics are responsible for the formation of an ionic crystal lattice. 3. List the key components of a covalent bond and how electrostatics are responsible for holding neutral atoms together. 4. Describe metalic bonding and the role of the "electron sea." 5. Write elemental dot structures for both ions and neutral atomic species.	Valence Electrons and Dots
Homework Problems 50.1 Ionic bonding is the electrostatic attraction beween two oppositely charged ions. How are the ions initially created? 50.2 Coulombs law describes the potential energy that exists when ions are separated a distance "r". Calculate the potential energy for two opposite charges (Q₁ = 1 Q₂ = -1) at a distance of r = 1.0 meter and r = 2 meter. Which potential energy is lower? Nature prefers low energy situations. What does nature prefer for oppositely charged ions? 50.3 Covalent bonds are like peanut butter sandwiches. Two slices of bread won't stick to themselves. However, if you spread peanut butter between them, the two bread pieces will stick together only because they're both attraced to the peanut butter. In the covalent bond, what are the bread slices and what is the peanut butter? 50.4 Unlike ionic bonds where electrons are transferred, covalent bonds form when electrons are... a. captured b. localized c. shared d. stolen e. present 50.5 Why are atoms attracted to the electrons in a covalent bond? 50.6 What is an electron sea and how does it accomplish metallic bonding? 50.7 Write the electron configurations and Lewis dot structures for each of the following species. a. Na b. Ar c. O d. O^2- e. Cl f. Cl^- g. Ca h. Ca⁺² Click and drag the region below for correct answers 50.1 Ions are created from neutral atoms when an electron from one is transferred to the other. This leaves the donor atom positively charged (cation) and the recipient atom negatively charged (anion). 50.2 When r = 1 m Energy = - 2.31 x 10^-28 J When r = 2 m Energy = -1.16 x 10^-28 J Since - 2.31 x 10^-28 J < -1.16 x 10^-28 J nature prefers a distance of 1.0 m vs. 2.0 m Short story: Opposite charges have the least potential energy when close together. 50.3 Each slice of bread is a non-metal atom. The peanut butter is what both bread slices are "attracted to", which are the electrons in the space between the atoms. 50.4 Shared 50.5 The atoms have positively charged nucleii that are attracted to the negatively charged electrons. 50.6 The electron sea consists of electrons that were once found on a single metal atom. However, when many metal ions are present, as is the case for a metal object, the electrons are free to circulate in and amongst the metal atoms. For example, if you filled a beaker with marbles (metal atoms) and then added water (electron sea) the electrons would be free to flow but the marbles would be stuck in place. 50.7 Click here for answers.

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Wednesday March 27, 2024 Day 47 Ionic Bonding and Lattice Energy
Textbook Reading 9.4: Ionic Bonding	Course Lectures 9.3 pdf Video Lattice Energy
Ionic Bonding	Practice Problem: Lattice Energy and Ionic Bond Strength
Objectives 1. Write Coulomb's law for "Force" and "Energy" 2. Describe how changes in distance and charge affect the attractive forces between ions. 3. Describe how changes in distance and charge affect the lattice energy. 4. Predict relative melting point differences for ionic solids based upon their lattice energies.	Lattice Energies and Melting Point Temperatures
Homework Problems 51.1 Consider the salts CsCl, NaCl, KCl and LiCl. Use the relative sizes of the metal ions to list the salts in order of increasing cation-anion distance in a ionic lattice. 51.2 Coulombs law of electrostatic forces states that the attractive forces between ions increases as the distance between the ions decreases. (If you've ever played with magnets, it's the same effect ...the closer the magnets are to each other, the stronger their attraction). Use your answers to 51.1 to identify the cation/anion combination that experiences the greatest and weakest attractive forces. 51.3 It requires a lot of heat to melt an ionic solid. At high temperatures, the ionic bonds are broken and the ions are set free from their positions within the ionic lattice. This is to say that the ionic solid "melts." Use your results from 51.2 to predict which ionic solid would have the highest melting point temperature. Also identify the species with the lowest melting point temperature. 51.4 MgS and NaCl are made up of ions that are similarly sized. Yet, the melting point temperature of MgS is (>2000 ^oC) is much higher than that for NaCl is (~800 ^oC). Why do they have such dramatically different melting point temperatures even though the cation-anion spacings are similar? 51.5 When anions and cations collapse to form an ionic solid, a large amount of energy is released and this energy is referred to as the "Lattice Energy" of the solid. Because the process releases energy, it's exothermic and that's why lattice energies have negative values. Lattice energies are always quoted "per mole" because the amount of heat released depends on the amount of ionic solid that forms. Here are the lattice energies for the ionic solids refered to in 51.1 Which ionic combination releases more heat energy as the cations and anions collapsed to form the ionic solid? Salt Lattice energy LiCl - 834 kJ/mol NaCl -787 kJ/mol KCl -701 kJ/mol CsCl -657 kJ/mol 51.6 Salts which have high lattice energies reach lower potential energies as the solid forms. These salts are more stable, lower in energy, have stronger ionic attractions and therfore higher melting point temperatures. Using only the lattice energy values, put the following salts in order of increasing melting point temperature. Salt Lattice energy KBr - 671 kJ/mol SrO -3217 kJ/mol CaO -3414 kJ/mol KCl -701 kJ/mol 51.7 Using only your periodic table, determine which of the following ionic solids you'd expect to have the greatest lattice energy? Why? NaCl MgO Al₂O₃ 51.8 Using only your periodic table, match each of the following ionic solids with its lattice energy; Al₂O₃ - 649 kJ/mol NaCl - 786 kJ/mol B₂O₃ - 1858 kJ/mol AlPO₄ - 7509 kJ/mol KCl - 15162 kJ/mol K₂CO₃ - 18730 kJ/mol 51.9 Using only your periodic table determine for each pair which should have the highest melting point temperature. Explain your answer. a. Al₂O₃ vs. Al₂Se₃ b. ZnO vs. NaCl c. MgF₂ vs. MgI₂ d. LiF vs. MgO Click and drag the region below for correct answers 51.1 smallest distance LiCl ... NaCl ... KCl ... CsCl 51.2 Greatest attractive force ... closest together (small ions) LiCl Least attractive forxe ... furthest apart (large ions) CsCl 51.3 Highest T_melt LiCl ... Lowest T_melt: CsCl 51.4 The cation-anion distances for MgS and NaCl are approximately the same. However, attractive forces also depend on the charges of the ions and in this case the Mg²⁺ and S^2- experience about 4x the attractive force of the Na⁺ and Cl^- ions. Being more strongly held, the MgS requires more heat and higher temperatures to melt. 51. 5 LiCl releases more heat energy than any of the others. 51.6 T_melt: KBr < T_melt: KCl < T_melt: SrO < T_melt: CaO 51.8 KCl 649 kJ/mol NaCl 786 kJ/mol K₂CO₃ 1858 kJ/mol AlPO₄ 7509 kJ/mol Al₂O₃ 15162 kJ/mol B₂O₃ 18730 kJ/mol 51.9 a. Al₂O₃ b. ZnO c. MgF₂ d. MgO

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Thursday March 28, 2024 Day 48 Covalent Bonding and Lewis Structures
Textbook Readings: 9.5: Covalent Bonding: Lewis Structure	Course Lecture 9.4 pdf Video Covalent Bonding
Covalent Bond Energy and Length (Through 3:06)	Chemical Bonding - Ionic vs. Covalent Bonds
Objectives 1. Describe how and why two hydrogen atoms experience i. repulsion ii. attraction and iii. repulsion as they are pushed together. 2. Draw Lewis dot structures for molecules containing oxygen, hydrogen, copper and nitrogen.
Homework Problems 52.1 Why does the potential energy of two atoms decrease as they are pushed closer together and the covalent bond begins to form? 52.2 What does the term "bond length" refer to and what is true for the molecule's potential energy at that point? 52.3 Why are two neutral atoms attracted to each other in a covalent bonding situation? 52.4 When neutral atoms are pushed to separation distances shorter than the "bond length", why does the potential energy increase. 52.5 Draw Lewis structures for each of the following molecules. Use "dots" when representing bonds. a. CCl₄ b. CCl₂O c. NH₃ d. H₂O e. H₂ f. O₂ g. N₂ h. OBr^- i. H₃O⁺ 52.6. For each of the molecules in 52.5, visibly verify that all atoms have either 8 electrons (octet) or 2 electrons (duet) Click and drag the region below for correct answers 52.1 As two neutral atoms are brought together, their outer most valence electrons begin to overlap. Eventually, there is enough electron density in the region between 52.2 Bond length refers to the "comfortable", low energy separation distance between atoms in a covalent bond. 52.3 Actually, the atoms aren't attracted to each other. Rather, the positively charged nucleii are attracted to the same high density that exists in the covalent bond region. Since both nucleii are attracted to the same electrons (remember opposite charges attract), it only seems that the atoms are attracted to each other. 52.4 When the atoms are separated by distances shorter than the low energy bond length, the energy increases as the repulsion between positively charged nucleii dominates tending to want to push the atoms further apart. 52.5 Click here for answers. 52.6 You're on your own on this one. Just be sure to show your work! :)

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Friday March 29, 2024 Day 49 Electronegativity and Bond Polarity
Textbook Readings: 9.6: Electronegativity and Bond Polarity	Course Lectures 9.9 pdf Video Electronegativity 9.10 pdf Video Bond Polarity
The Periodic Table: Atomic Radius, Ionization Energy, and Electronegativity (Beginning at 6:20)	The Chemical Bond: Covalent vs. Ionic and Polar vs. Nonpolar
Objectives 1. Describe what electronegativity means. 2. Interpret delta E_n value to determine bond polarity 3. Draw dipole moment vectors (arrows) to signify the bond polarity 4. Calculate dipole moments and percent diopole character.	9.10 Bond Polarity
Homework Problems 53.1 Two young children have a bag of candy that they're supposed to share. However, one child, "Terry", takes more than half leaving "Alyssa" with fewer candy pieces. Explain in your own words how this situation relates to polar covalent bonding.
53.2 Electronegativity (E_n) is the term we use to describe an atom's ability to attract bonding electrons. The higher the E_n value, the greedier an atom is for bonding electrons. Use the E_n periodic table above to determine which of the two elements is greedier. a. Cl or Cl b. C or Cl c. C or S d. C or O e. C or N f. C or F 53.3 What four elements have the greatest electronegativity and are most likely to be involved in a polar covalent bond? 53.4 In bonding situations, we will compare the E_n values of the bonded atoms by calculating the difference between their respective electronegativities (abbreviated ΔE_n). Note that this difference is reported as a positive number. The ΔE_n value is then used to determine the bond type as either ionic, polar covalent, or non-polar (a.k.a. pure covalent) according to the following guidelines. Use E_n values and the guidelines above to determine if the bond between the two atoms is ionic, polar covalent or Pure (non-polar) covalent. a. C & N b. N & S c. K & F d. Sr & F e. N & Cl f. N & O g. I & I h. Cs & Br i. P & O 53.5 The "dipole moment vector" is an arrow used to indicate the direction electrons drift in a polar covalent bond as a result of electronegativity differences. Additionally, the arrow has a "+" sign at one end to indicate how the drifting electrons have left that side of the bond slightly positively charge. Draw the atoms, bonds and dipole moment vector for the polar covalent bonds you identified in problem 53.4 Click and drag the region below for correct answers 53.1 The two children are atoms attracted to the same electrons (candy). Their bond is polar because one child finishes with more of the candy than the other. 53.2 a. Neither. They are identical b. Chlorine c. Sulfur d. Oxygen e. Nitrogen f. Fluorine 53.3 N, O, F, & Cl 53.4 a. C & N ΔE_n = 0.5 Polar Covalent b. N & S ΔE_n = 0.5 Polar Covalent c. K & F ΔE_n = 3.2 Ionic d. Sr & F ΔE_n = 3.0 Ionic e. N & Cl ΔE_n = 0.0 Pure Covalent (non-polar) f. N & O ΔE_n = 0.5 Polar Covalent g. I & I ΔE_n = 0.0 Pure Covalent (non-polar) h. Cs & Br ΔE_n = 2.1 Ionic ....just barely i. P & O ΔE_n = 1.4 Polar Covalent 53.5 Answers available here.

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