Ch7 Practice Problems KEY

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1 Ch. 7 Spring 2024 CHM113 Chapter 7 Problem Set 1. The elements in the ________ period of the periodic table have a core-electron configuration that is the same as the electron configuration of neon. (MC) A) first C) third B) second D) fourth 2. Consider the element with the electron configuration [Kr]5s 2 4d 7 . This element is A. a representative element. B. a transition metal. C. a nonmetal. D. an actinide element. E. a noble gas. 3. In which set of elements would all members be expected to have very similar chemical properties? (MC) A) P, Se, I B) Cl, Br, Na C) Si, As, Te D) Ne, Na, Mg E) Br, I, At 4. Which of the following has valence electrons in the 3 rd shell a. Ne b. B c. Zn d. Ga e. Al 5. Which have 6 valence electrons? a. Halogens b. Alkali metals c. Chalcogens d. Noble gases e. Period 6 elements 6. Valence electrons highlighted incorrectly? a. Fe: [Ar] 4s 2 3d 6 b. Cu: [Ar] 4s 1 3d 10 c. Mg: 1s 2 2s 2 2p 6 3s 2 d. V: [Ar] 4s 2 3d 3 e. As: [Ar] 4s 2 3d 10 4p 3

2 Ch. 7 Spring 2024 Effective Nuclear Charge: Z eff Z eff = Z - S → Z = # protons; S = # inner (core) e - Slaters Rules: S = (# of n e-)( 0.35) + (#of n-1 e-)(0.85) + (# of n-2 or less e-)(1) → don’t count the electron itself! 7. Fill in the arrows for the main group trends. A. How does it change L to R? Why? B. How does it change Top to Bottom? Why? 8. Which atom’s valence electrons experience the greatest Z eff ? • Write the electron configuration • Calculate Z eff with and without Slater’s rules. Example 1: N or O N: O: Example 2: O or S S: 9. Which atom’s 1s orbital lies the closest to the nucleus? A. Ar B. Ne C. He 10. Which is False when discussing Effective Nuclear Charge? a. Electrons are attracted to the protons in the nucleus and are repulsed by other electrons. b. VE’s can be shielded from the nucleus by the core electrons and by other valence electrons . c. Z eff might be larger than predicted because the valence electron moving around in its orbital has the potential to exist closer to nucleus and electron sees higher positive charge. d. Z eff increases L → R across a row because number of core electrons stays the same but number of protons increases. e. Z eff decreases (slightly) from top to bottom down a group because the Z-S value is the same but larger e cores don’t shield as well . 1 2 H He 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar 19 20 31 32 33 34 35 36 K Ca Ga Ge As Se Br Kr 37 38 49 50 51 52 53 54 Rb Sr In Sn Sb Te I Xe 55 56 Cs Ba [He] 2s 2 2p 3 or 1s 2 2s 2 2p 3 Z eff = +5 Slater’s rules: Z eff = +3.90 [He] 2s 2 2p 4 or 1s 2 2s 2 2p 4 Z eff = +6 Slater’s rules: Z eff = +4.55 [Ne] 3s 2 3p 4 or 1s 2 2s 2 2p 6 3s 2 3p 4 Z eff = +6 Slater’s rules: Z eff = +5.45 Z eff increases Z eff increases sligh

3 Ch. 7 Spring 2024 11. On the periodic table below, indicate the following general trends for the periods and groups: atomic radius , ionization energy , metallic character , and electron affinity . Atomic radius: decreases from left to right across the period, increases from top to bottom down the group **Ionic radius: ions increase in size down a group, cations are smaller than their parent atom while anions are larger than their parent atom Ionization energy: increases from left to right across the period, decreases from top to bottom down the group Metallic character: decreases from left to right across the period, increases from top to bottom down the group Electron affinity: increases from left to right across the period. 12. Give the the correct order for atomic radius for Mg, Na, P, Si and Ar. Ar < P < Si < Mg < Na 13. Which has the largest atomic radius? Why? i. P or S smaller Z eff ii. O or S larger valence shell 14. Which has the largest radius? Why? i. Ca or Ca 2+ larger valence shell ii. S or S 2- greater electron repulsions, same Z eff , electrons spread out iii. O 2- or S 2- same trend as atomic radius All arrows show direction of increasing value

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4 Ch. 7 Spring 2024 15. Which molecule has the longest bond? a. C — H b. C — O c. C — N d. C — Br e. C — Cl 16. Following is an isoelectronic series. Arrange this series in order of decreasing ionic radius : Br - , Rb + , Se 2- , Sr 2+ . Sr 2+ < Rb + < Br - < Se 2- What is the electron configuration (full or abbreviated) for this series? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 17. Which of the following statements are false ? a. All atoms in an isoelectronic series are the same size. b. All atoms in an isoelectronic series have the same number of valence electrons. c. O 2- , F - , Ne, Na + , Mg 2+ is an example of an isoelectronic series. d. If ions are isoelectronic, the ion with more protons will have a smaller radius. e. If ions are all anions, then their radii follow the same trend as neutral atoms. 18. Which equation correctly represents the first ionization energy (I 1 ) of sodium? a. Na - (g) → Na (g) + e - b. Na (s) → Na + (s) + e - c. Na (g) + e - → Na - (g) d. Na (g) → Na + (g) + e - e. Na + (g) + e - → Na (g) 19. What is the chemical equation for the first ionization energy (I 1 ) for the following atoms? What are the electron configurations for the atom and its ion? a. Li (g) → Li + (g) + e - Li: 1s 2 2s 1 or [He]2s 1 Li + : 1s 2 b. Al (g) → Al + (g) + e - Al: 1s 2 2s 2 2p 6 3s 2 3p 1 or [Ne]3s 2 3p 1 Al + : 1s 2 2s 2 2p 6 3s 2 or [Ne]3s 2 20. Of the choices below, which gives the order for first ionization energies? (MC) A) Kr > Se > Br > Ga > Ge B) Kr > Br > Se > Ge > Ga C) Ga > Br > Ge > Kr > Se D) Ga > Ge > Se > Br > Kr E) Br > Se > Ga > Kr > Ge

5 Ch. 7 Spring 2024 21. Which has the highest 2 nd ionization energy: Ca or K? Why? Symbolic/Equation Electron configuration Ca IE 1 IE 2 K IE 1 IE 2 22. Which of the following explains why electron configurations for chromium and copper disobey Aufbau order? a. Filled and half-filled subshells are especially stable. b. No two electrons can have the same energy. c. Electrons fill the lowest energy orbitals first. d. Two elections can occupy same orbital but must have different spins. e. Remove electrons from the p/s orbitals first, then the (n-1) d orbitals. 23. Which of the following explains the electron configurations for cations of transition metals? a. Filled and half-filled subshells are especially stable. b. No two electrons can have the same energy. c. Electrons fill the lowest energy orbitals first. d. Two elections can occupy same orbital but must have different spins. e. Remove electrons from the p/s orbitals first, then the (n-1) d orbitals. 24. What is the electron configuration of Zn? a. [Ar]4s 2 3d 10 b. [Ar]4s 2 4d 8 c. [Ar]3d 10 d. [Ar]4d 10 25. What is the electron configuration of Zn 2+ ? a. [Ar]4s 2 3d 8 b. [Ar]4s 2 4d 8 c. [Ar]4d 10 d. [Ar]3d 10 I 1 : Ca → Ca + + e- Ca: [Ar]4s 2 (removing one will not remove a core electron) I 2 : Ca + → Ca 2+ + e- Ca + : [Ar]4s 1 (removing one will not remove a core electron) I 1 : K → K + + e- K: [Ar]4s 1 (removing one will not remove a core electron) I 2 : K + → K 2+ + e- K + : [Ar] (removing one REMOVES a core electron!!) 1s 2 2s 2 2p 6 3s 2 3p 6

6 Ch. 7 Spring 2024 26. Where are the groups that contain atoms with positive electron affinities? What does a positive electron affinity mean? a. Alkali metals b. Alkaline earth metals c. Chalcogens d. Noble gases e. Halogens 27. Which group has the greatest electron affinity (most negative)? a. Alkali metals b. Alkaline earth metals c. Chalcogens d. Noble gases e. Halogens 28. What does a more negative electron affinity mean? A. Greater ability to lose an electron, energy released (exothermic) B. Greater attraction to an added electron, energy absorbed (endothermic) C. Greater ability to lose an electron, energy absorbed (endothermic) D. Greater attraction to an added electron, energy released (exothermic) E. None of the above 29. Which of the following shows a reaction for a positive electron affinity? A. Ar (g) + e - → Ar - (g) B. Cl (g) → Cl + (g) + e - C. Na (g) + e - → Na - (g) D. He (g) → He + (g) + e - 30. Which of the following is not a good way to describe an atom with a positive electron affinity? A. Energy is absorbed in the process B. An electron will not attach itself to the neutral atom C. The negative ion is unstable and will not form D. Adding an electron to the atom is energetically unfavorable E. All of the above are accurate descriptions. 31. Why are the electron affinities of Group 5 elements more positive (less negative) than would be predicted by the general trend? _____ 32. Why are the electron affinities of Group 2 elements more positive (less negative) than would be predicted by the general trend? _____ 33. Why are the electron affinities of Group 8 elements more positive (less negative) than would be predicted by the general trend? _____ A. Stability of full s orbitals B. Stability of full p orbitals C. Stability of full s and p orbitals D. Stability of half full p orbitals D A C

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7 Ch. 7 Spring 2024 34. Consider the following electron configurations to answer the questions that follow: (i) 1s 2 2s 2 2p 6 3s 1 (ii) 1s 2 2s 2 2p 6 3s 2 (iii) 1s 2 2s 2 2p 6 3s 2 3p 1 (iv) 1s 2 2s 2 2p 6 3s 2 3p 4 (v) 1s 2 2s 2 2p 6 3s 2 3p 5 a. The electron configuration that belongs to the atom with the highest second ionization energy is (i) b. The electron configuration that belongs to the atom with the most negative electron affinity is (v) c. The electron configuration belonging to the atom with largest radius is (i) . 35. Which of the following is false ? Metals with high metallic character tend to more easily _________. a. lose electrons. b. form cations. c. oxidize. d. react with oxygen to form acidic oxides. e. react with water to form hydroxides, H 2 , and heat. 36. Which list correctly indicates the order of metallic character (from most metallic to least metallic)? a. O > Se > S b. Li > Na > K c. C > Ge > Si d. F > Cl > Br e. Sr > Ca > Mg 37. Consider Mg, Si, Fe, and S . Which would have the (or be)... a. Highest melting point? Fe b. Lowest ionization energy? Mg c. Greatest electron affinity? S d. Most easily oxidized? Mg e. Oxide that is acidic? S f. An electrical semiconductor? Si g. The least lustrous? S h. Exhibits multiple oxidation states Fe 38. Little is known about astatine because of its rarity and radioactivity. Make the following predictions: a. Is it a solid, liquid, or gas at room temperature? Solid Astatine is in the same family as iodine, which is solid, and a larger atom, so it would follow that it is solid as well. b. Is it a metal, non-metal, or metalloid? Non-metal It is to the far right of the periodic table in the halogens, so it is a nonmetal. c. What would be the chemical formula of the compounds it forms with sodium and aluminum? NaAt AlAt 3

8 Ch. 7 Spring 2024 Some Group Trends (7.7 & 7.8) Group 1A: The Alkali Metals • Alkali metals are soft, metallic solids. • The name comes from the Arabic word for ashes. • They are found only in compounds in nature, not in their elemental forms. • They have low densities and melting points. • They also have low ionization energies. • Their chemistry is dominated by the loss of their single s electron: M → M + + e – • With water: Their reactions are famously exothermic: 2M( s ) + 2H 2 O( l ) → 2MOH( aq ) + H 2 ( g ) • With oxygen: 4Li( s ) + O 2 ( g ) → 2Li 2 O( s ) ( oxide ) o Alkali metals (except Li) react with oxygen to form peroxides: 2Na( s ) + O 2 ( g ) → Na 2 O 2 ( s ) ( peroxide ) o K, Rb, and Cs also form superoxides: K( s ) + O 2 ( g ) → KO 2 ( s ) ( superoxide ) • With hydrogen: the hydrogen is present as H – , hydride ion . 2M( s ) + H 2 ( g ) → 2MH( s ) • High temps: They produce bright colors when placed in a flame. Group 2A: The Alkaline Earth Metals • Alkaline earth metals are harder, more dense, and have higher melting points than alkali metals. • Their ionization energies are low, but not as low as those of alkali metals. • Reactivity tends to increase as you go down the group. • Their chemistry is dominated by the loss of two s electrons: M → M 2+ + 2e – • With water: Ca( s ) + 2H 2 O( l ) → Ca(OH) 2 ( aq ) + H 2 ( g ) o Beryllium does not react with water and magnesium reacts only with steam, but the others react readily with water. • With oxygen: 2Mg( s ) + O 2 ( g ) → 2MgO( s ) ( oxide )

9 Ch. 7 Spring 2024 Trends for Selected Nonmetals Hydrogen • Although hydrogen and alkali metals have a single valence electron, the reactivity of hydrogen is very different from that of alkali metals. o It can either gain another electron to form the hydride ion, H – 2Na( s ) + H 2 ( g ) → 2NaH( s ) ▪ When in an ionic compound with a metal. These are referred to as metal hydrides o or lose its electron to become H + : 2H 2 ( g ) + O 2 ( g ) → 2H 2 O( l ) ▪ The aqueous chemistry of hydrogen is dominated by H + ( aq ). • It most often occurs as a colorless diatomic gas, H 2 like the other nonmetal gases • Reaction with nonmetals tends to form molecular compounds: ½ H 2 ( g ) + ½ Cl 2 ( g ) → HCl( s ) • Under extreme pressure, hydrogen can act like a metal and conduct electricity and heat Group 6A: The Oxygen Group (Chalogens) • As we move down the group, the metallic character increases. o Oxygen, sulfur, and selenium are nonmetals. o Tellurium is a metalloid. o The radioactive polonium is a metal. • Have low melting points and high ionization energies and densities Group 7A: The Halogens • The halogens are prototypical nonmetals. • The name comes from the Greek words halos and gennao : “salt formers”. • They have large, negative electron affinities. o Therefore, they tend to oxidize other elements easily in other words are very good oxidizing agents. • All halogens exist as diatomic molecules • Reactions with hydrogen form gaseous halides, all strong acids except for HF. ▪ H 2 ( g ) + X 2 → 2HX( g ) • They react directly with metals to form metal halides. • Fluorine is one of the most reactive substances known. ▪ 2F 2 ( g ) + 2H 2 O( l ) → 4HF( aq ) + O 2 ( g ) • Chlorine is one of the more industrially useful halogens: o Added to water to disinfect swimming pools: forms hypochlorous acid. ▪ Cl 2 ( g ) + H 2 O( l ) → HCl( aq ) + HOCl( aq )

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10 Ch. 7 Spring 2024 Group 8A: The Noble Gases • The noble gases have astronomical ionization energies. • Their electron affinities are positive. o Therefore, they are relatively unreactive. • They are found as monatomic gases. • Xe forms three compounds: o XeF 2 , XeF 4 (at right), XeF 6 • Kr forms only one stable compound: KrF 2 • The unstable HArF was synthesized in 2000. Allotropes • Allotropes are different forms of the same element at the same state. o Oxygen- ▪ O 2 and O 3 (ozone), and AO (atomic oxygen) o Sulfur – more than 30! ▪ most stable is S 8 o Carbon – 8 allotropes ▪ most common is graphite o Phosphorus – 5 allotropes ▪ diphosphorus (P 2 ) (by heating white phosphorus to high temp) ▪ white (P 4 ), most common (glows) ▪ red (matches) ▪ violet ▪ black (most stable)

11 Ch. 7 Spring 2024 Chapter 7 Reference Information