Ch. 3 Answer Key 1. The Greeks believed that all matter is made of elements. We currently believe the same thing. However, the Greeks believed that there were 4 elements: earth, water, air and fire. Instead, we have a Periodic Table which contains 118 elements. The smallest unit of an element is an atom. 2. The early alchemists were able to make some discoveries about metals like mercury and antimony and some nonmetal elements such as sulfur. They also learned how to prepare acids. 3. Boyle s most important contribution to science were in his experiments. He determined that a substance was an element if it can not be broken down to simpler parts. For example H 2 O can be broken down to form two atoms of H and 1 atom of O. Hydrogen and oxygen are elements. 4. Out of the 112 elements known in 1999, 88 of these elements occur naturally and the rest have been made in laboratories. The most common elements on earth are, oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, hydrogen, titanium, chlorine, phosphorus, manganese, carbon, sulfur, barium, nitrogen, and fluorine. 5. Oxygen is also found in rocks, sand, and soil and is more commonly found in compounds than on its own as an element. Examples of oxygen in compound form include H 2 O, CO 2, FeO, SiO 2 etc. 6. The most abundant elements in human body are oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, magnesium, potassium, sulfur, sodium all of which are among the most abundant elements on earth. 7. Boron-B, Carbon-C, Fluorine-F, Hydrogen-H, Iodine-I, Nitrogen-N, Oxygen-O, Phosphorus-P, Potassium-K, Sulfur-S, Uranium-U, Vanadium-V, Yttrium-Y, Tungsten-W 8. Potassium-K, Gold- Au, Silver-Ag, Antimony-Sb, Iron-Fe. 9. a. Neon- Ne b. Nickel- Ni c. Potassium-K
d. Silicon- Si e. Barium- Ba f. Silver- Ag 10. 11. 12. a. Fe- iron b. Cl- chlorine c. S- sulfur d. U- uranium e. Ne- neon f. K- potassium a. Cu- copper b. Co- cobalt c. Ca- calcium d. C- carbon e. Cr- chromium f. Cs- cesium g. Cl- chlorine h. Cd- cadmium a. False, most natural materials are mixtures of pure substances (compounds and elements). b. True c. False, molecules are made up of tiny particles called atoms 13. The law of constant composition states that a given compound always has the same composition, regardless of where it comes from. A given compound always has the same numbers and types of atoms. For example, CO 2 contains one carbon and 2 oxygen atoms. C 6 H 12 O 6 contains 6 carbon, 12 hydrogen and 6 oxygen atoms. 14. A compound is two or more elements chemically bonded. 15. The mass of one atom of any element is unique. For hydrogen the average mass for an atom is 1.008 amu (from the periodic table). An average oxygen atom has a mass of 15.999 amu. Therefore, the compound of water (H 2 O) has a mass of about 18 amu. There is a ratio of masses for each element and a ratio of atoms and they are related. 16. a. PCl 3
b. B 2 H 6 c. CaCl 2 d. CBr 4 e. Fe 2 O 3 f. H 3 PO 4 19. Neutrons are uncharged particles that are found in the nucleus of atoms. They are incredibly tiny, even relative to the tiny size of a single atom. 20. Protons are the positively charged particles that are found in the nucleus of atoms. They are incredibly tiny, even relative to the tiny size of a single atom. 21. Neutrons are slightly more massive than protons but it is close enough for us to say that they are approximately the same. Electrons have almost no mass relative to protons and neutrons. We usually say that they have a mass of 0. Therefore, almost all of the mass for an atom comes from the protons and neutrons in the tiny nucleus. However, electrons determine the chemical properties for an atom. 22. Although the nucleus of an atom is very important, it is the electrons of the atoms that determine it s chemical properties. 23. False Corrected: Atoms that have the same number of PROTONS but a different number of NEUTRONS are called isotopes. 24. False Corrected: The mass number of a nucleus represents the sum of the number of protons and neutrons in the nucleus. 26. Not all atoms of the same element are identical. There are different isotopes which have different numbers of neutrons and therefore different mass numbers (P + + N). 27. a. Ge Atomic number = 32 b. Zn Atomic number = 30 c. Cr Atomic number = 24 d. W (tungsten) Atomic number = 74 e. Sr Atomic number = 38 f. Co Atomic number = 27
g. Be Atomic number = 4 h. Li Atomic number = 3 28. 29. 17 a. 8 O 37 b. 17 Cl c. 60 27 Co d. 57 26 Fe e. 131 53 I f. 7 Li 3 244 a. 94 Pu 241 b. 95 Am P + = 94 N = 150 P + = 95 N = 146 227 c. 89 Ac 133 d. 55 Cs 193 e. 77 Ir P + = 77 P + = 89 P + = 55 N = 116 N = 138 N = 78 56 f. 25 Mn P + = 25 N = 31 30. Name Symbol Atomic Number Mass Number Neutrons Sodium 23 11 Na 11 23 12 Nitrogen Barium 15 7 136 56 N Ba 7 15 8 56 136 80 Lithium 9 3 Li 3 9 6 Boron 11 5 B 5 11 6
31. The Periodic Table is arranged in order of increasing atomic number (number of protons). Originally, it was arranged into families based on similar chemical and physical properties. 32. Elements with similar chemical properties (families) are found in vertical columns called groups on the Periodic Table. 33. Metals tend to be (1) good conductors of heat and electricity, (2) malleable, (3) ductile, and (4) lustrous. Something is malleable if it can be dented and flattened with a hammer. Ductile means that a thing can be stretched into wires. Lustrous is a metallic shininess. 34. Metals are found below and to the left of the stair-step. There are many more metals than nonmetals. 35. Mercury (Hg) is a liquid at room temperature. 36. Nitrogen (N 2 ), oxygen (O 2 ), fluorine (F 2 ), chlorine (Cl 2 ) and all of the noble gases (He, Ne, Ar, Kr, Xe and Rn) are gases at room temperature. 37. Mercury (Hg) is a metal that exists as a liquid at room temperature and bromine (Br) is a nonmetal that exists as a liquid at room temperature. 38. Metalloids are elements that exhibit properties between metals and nonmetals. They tend to be brittle and lustrous. They are found along the stair-step of the Periodic Table. 39. (a) Iodine (I) is in group 17 (VIIA) and is a halogen (b) Calcium (Ca) is found in group 2 (IIA) and is an alkaline earth metal. (c) Sodium (Na) is found in group 1 (IA) and is an alkali metal. (d) Lithium (Li) is a found in group 1 (IA) and is an alkali metal. (e) Krypton (Kr) is found in group 18 (VIIIA) and is a noble gas (f) Sodium (Na) is found in group 1 (IA) and is an alkali metal. (g) Neon (Ne) is found in group 18 (VIIIA) and is a noble gas 40. (a) Rubidium is an alkali metal (metal) that is found in group 1 (IA). (b) Germanium is a metalloid (semimetal) that is found in group 14 (IVA). (c) Magnesium (Mg) is an alkaline earth metal (metal) that is found in group 2 (IIA).
(d) Titanium (Ti) is a transition metal (metal) found in group 4. (e) Iodine is a halogen (nonmetal) found in group 17 (VIIA). 41. Most elements are found in nature in compound form because they have reacted with other elements. 42. Elements from group 18 (VIIIA) are referred to as noble or inert gases because they unreactive and stand apart from other elements for that reason. 45. [1] 10 (b) [2] 23 (d) [3] 10 (b) [4] 48 (h) [5] 25 (f) [6] 24 (e) [7] 2 (a) [8] 21 (c) [9] 36 (g) [10] 76 (i) 46. a. Co 2+ 27 P + 25 e - CoO (2+) + (2-) = 0 b. Co 3+ 27 P + 24 e - Co 2 O 3 2(3+) + 3(2-) = 0 (6+) + (6-) = 0 c. Cl 1-17 P + 18 e - CaCl 2 (2+) + 2(1-) = 0 (2+) + (2-) = 0 d. K 1+ 19 P + 18 e -
K 2 O 2(1+) + (2-) = 0 (2+) + (2-) = 0 47. a. Ca Ca 2+ + 2e - 20 P + 20 P + 20 e - 18 e - b. P + 3e - P 3-15 P + 15 P + 15 e - 18 e - c. Br + e - Br 1-35 P + 35 P + 35 e - 36 e - d. Fe Fe 3+ + 3e - 26 P + 26 P + 26 e - 23 e - 48. a. 53 I 1- b. 38 Sr 2+ c. 55 Cs 1+ d. 88 Ra 2+ 49. Ionic compounds tend to have very high melting and boiling points. They also tend to increase the electrical conductivity of water because the ions are able to move around. Ionic compounds are also brittle and tend to break along straight lines of alternating positive and negative charges. Nonionic compounds tend to have low melting and boiling points. Nonionic compounds also tend to be softer if they are not metals and don t usually break in straight lines. 50. An ionic compound is able to increase the electrical conductivity of water because the ions are able to move around freely. As a solid, ionic compounds do not conduct electricity well because ions do not move around freely.
51. The total number of positive charges (protons) must equal the total number of negative charges (electrons) so that the crystals of an ionic compound have no net charge. A normal size or larger (macroscopic) sample of a compound ordinarily has no charge. 52. a. Fe 3+ + P 3- FeP b. Fe 3+ + S 2- Fe 2 S 3 c. Fe 3+ + Cl 1- FeCl 3 d. Mg 2+ + Cl 1- MgCl 2 e. Mg 2+ + O 2- MgO f. Mg 2+ + N 3- Mg 3 N 2 g. Na 1+ + P 3- Na 3 P h. Na 1+ + S 2- Na 2 S