4.2: Answer Key

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1. All matter is composed of atoms; atoms of the same element are the same, and atoms of different elements are different; atoms combine in whole-number ratios to form compounds.

a. Sodium---alkali metal

b. Magnesium---Alkaline earth metal

c. Calcium---Alkaline earth metal

d. Chlorine---halogen

e. Potassium---Alkali metal

5. Most of the alpha particles went through the metal sheet because atoms are mostly empty space.

7. Electrons are in orbit about the nucleus.

9. The electron weighs the least. The protons and neutrons are found in the nucleus while electrons are located outside the nucleus.

11. Proton, electron

13. Least, outside

15. a. Z = 8; O; atomic oxygen

b. Z = 27; Co; cobalt

c. Z = 33; As; arsenic

e. Z = 90; Th; thorium

17. a. P b. Mo c. Be

19. a. Ag b. S c. N d. Ne

21. a. 86 b. 74 c. 24 d. 4

23. Column 1 is the alkali metals. Column 2 is the alkaline earth metals. Columns 3 - 12 are the transition metals.

25. The transition metals can exist in more than one charge state. They have variable charge.

27. Calcium and Barium (belong to same group).

29. Magnesium; Beryllium

31. Helium; Xenon; Neon

33. metal; transition metal.

35. a,d

37. a. 1A (1) b. 1A (1) c. 8A (18) d. 6A (16)

39.

Chemical Symbol	Group Number	Group Name	Metal or Non-metal
Br	7A (17)	Halogens	Non-metal
Sr	2A (2)	Alkaline earth metals	metal
Ne	8A (18)	Noble gases	Non-metal
K	1A (1)	Alkali metal	metal

41. a and d

43. a and b

45. a. 27 b. 38 c. 54 d. 28

47. a. 10 b. 2 c. 46 d. 30

49. a. Li, Li⁺, 2nd period, group 1

b. F, F^–, 2nd period, group 17

c. Al, Al³⁺, 3nd period, group 13

51. a. 2 b. 3 c. 3 d. 1

53.

a. 1+

b. 2−

c. 2+, 3+

55. SO₃ is sulfur trioxide, while SO₃²⁻ is the sulfite ion.

57. All isotopes of nitrogen have the same atomic number (Z = 7). Yes, all isotopes of the same element have the same Z.

59. a. Z=1, A=3 b. Z=20, A=42 c. Z=73, A=182 d. Z=24, A=52

61. a. 26 b. 22 c. 2

63. a. b. c. d. e.

65.

a. protons=43; neutrons=54; electrons=43

b. protons=49; neutrons=64; electrons=49

c. protons=28; neutrons=35; electrons=28

d. protons=26; neutrons=29; electrons=26

67.

a. protons=82; neutrons=125; electrons=82

b. protons=8; neutrons=8; electrons=8

c. protons=55; neutrons=82; electrons=55

d. protons=19; neutrons=21; electrons=19

69. This iron atom has 26 protons and 56 − 26 = 30 neutrons.

71. a. He b. B c. Bi & P

73.

Number of protons	Number of neutrons	Element name	Isotope Symbol
80	120	Mercury
26	29	iron
1	2	Hydrogen

75. If "CO" was written as the chemical symbol for cobalt, it would be the same as the chemical formula for carbon monoxide. This ambiguity would create a lot problems such as in labeling and might lead to life-threatening danger. And The chemical symbol is ALWAYS written with the first letter in uppercase and the second letter in lowercase.

77. a) Iron, 26 protons, 24 electrons, and 32 neutrons;

(b) iodine, 53 protons, 54 electrons, and 74 neutrons

79. If the atomic number of uranium is 92, then that is the number of protons in the nucleus. Because the mass number is 235, then the number of neutrons in the nucleus is 235 − 92, or 143.