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The answers listed here are from the Complete Solutions Guide, in which rounding is carried out at each intermediate step in a calcu- lation in order to show the correct number of significant figures for that step. Therefore, an answer given here may differ in the last digit from the result obtained by carrying extra digits throughout the entire calculation and rounding at the end (the procedure you should follow). Chapter 2 19. ClF 3 21. All the masses of hydrogen in these three compounds can be expressed as simple whole-number ratios. The g H/g N in hydrazine, ammonia, and hydrogen azide are in the ratios 6:9:1. 23. O, 7.94; Na, 22.8; Mg, 11.9; O and Mg are incorrect by a factor of ± 2; correct formulas are H 2 O, Na 2 O, and MgO. 25. d(nucleus) ± 3 ² 10 15 g/cm 3 ; d(atom) ± 0.4 g/cm 3 27. Since all charges are whole-number multiples of 6.40 ² 10 ³ 13 zirkombs, then the charge on one electron could be 6.40 ² 10 ³ 13 zirkombs. However, 6.40 ² 10 ³ 13 zirkombs could be the charge of two elec- trons (or three electrons, etc.). All one can conclude is that the charge of an electron is 6.40 ² 10 ³ 13 zirkombs or an integer frac- tion of 6.40 ² 10 ³ 13 . 29. If the plum pudding model were correct (a diffuse positive charge with electrons scattered throughout), then ± particles should have traveled through the thin foil with very minor deflections in their path. This was not the case because a few of the ± particles were deflected at very large angles. Rutherford reasoned that the large deflections of these ± particles could be caused only by a center of concentrated positive charge that con- tains most of the atom’s mass (the nuclear model of the atom). 31. The atomic number of an element is equal to the number of protons in the nucleus of an atom of that element. The mass num- ber is the sum of the number of protons plus neutrons in the nucleus. The atomic mass is the actual mass of a particular isotope (including electrons). As we will see in Chapter 3, the average mass of an atom is taken from a measurement made on a large number of atoms. The average atomic mass value is listed in the periodic table. 33. a. The noble gases are He, Ne, Ar, Kr, Xe, and Rn (helium, neon, argon, krypton, xenon, and radon). Radon has only radioactive isotopes. In the periodic table, the whole number enclosed in parentheses is the mass number of the longest-lived isotope of the element. b. promethium (Pm) and technetium (Tc) 35. a. Five; F, Cl, Br, I, and At; b. Six; Li, Na, K, Rb, Cs, Fr (H is not considered an alkali metal.) c. 14; Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; d. 40; all elements in the block defined by Sc, Zn, Uub, and Ac are transition metals. 37. a. 12 p, 12 n, 12 e; b. 12 p, 12 n, 10 e; c. 27 p, 32 n, 25 e; d. 27 p, 32 n, 24 e; e. 27 p, 32 n, 27 e; f. 34 p, 45 n, 34 e; g. 34 p, 45 n, 36 e; h. 28 p, 35 n, 28 e; i. 28 p, 31 n, 26 e 39. 151 63 Eu 3 ´ ; 118 50 Sn 2 ´ 41. a. Lose 2 e ³ to form Ra 2 ´ ; b. Lose 3 e ³ to form In 3 ´ ; c. Gain 3 e ³ to form P 3 ³ ; d. Gain 2 e ³ to form Te 2 ³ ; e. Gain 1 e ³ to form Br ³ ; f. Lose 1 e ³ to form Rb ´ 43. AlCl 3 , aluminum chloride; CrCl 3 , chromium(III) chloride; ICl 3 , iodine trichloride; AlCl 3 and CrCl 3

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