Summer Assignment Chapter 2 PROBLEMS pg. 69 #7, 11, 13, 15, 17, 20, 21, 22, 27, 28, 30, 31, 33, 35, 38, 40, 41, 43, 45, 47, 49, 55, 56, 57, 58, 60, 61, 64, 67, 69, 71, 87 7 The diameter of a neutral helium atom = 1 10 2 pm. Suppose that we could line up helium atoms side by side in contact with one another. Approximately how many atoms would it take to make the distance from end to end 1 cm? First, convert 1 cm to picometers. 1 cm 0.01 m 1 cm 1 pm 1 10 12 m = 1 1010 pm? He atoms = (1 10 10 pm) 1 He atom 1 10 2 pm = 1 108 He atoms 11 What do we call atoms of the same elements with different mass numbers? Isotopes. 13 What is the mass number of an iron atom that has 28 neutrons? For iron, the atomic number Z is 26. Therefore the mass number A is: A = 26 + 28 = 54 15 For the following atoms, determine the number of protons and neutrons. Isotope 3 2 He 2 He 12 Mg 12 Mg 22Ti 35Br 78Pt No. Protons 2 2 12 12 22 35 78 No. Neutrons 1 2 12 13 26 44 117 17 Give the symbol for the following isotopes: (a) Z= 11 A = 23 23 11Na (b) Z= 28 A = 64 64 28Ni 20 State two differences between a metal and a nonmetal. Metals conduct heat and electricity, are shiny & malleable; nonmetals are poor conductors, generally dull and brittle. 21 Write the names and symbols for four elements in each of the following categories: (a) nonemetal: phosphorous P, bromine Br, neon, Ne, carbon C (b) metal: iron Fe, cesium Cs, iridium, Ir, praseodymium Pr (c) metalloid: silicon Si, germanium Ge, boron B, antimony Sb 22 Define, with two examples, the following terms: (a) Alkali metals: (1 st column) Sodium, rubidium; (b) alkaline earth metals: (2 nd column) barium, beryllium; (c) halogens: (7 th column) fluorine, iodine; (d) noble gases: (8 th column) xenon, krypton 27 What is the difference between an atom and a molecule? An atom is the smallest representative unit of an element. A molecule is the smallest representative unit of a (non-ionic) compound, composed of two or more atoms chemically bonded. 28 What are allotropes? Allotropes are different physical forms of the same element. Examples? graphite and diamond are two allotropes of carbon.
2 SUMMER ASSINGMENT ANSWER KEY: CHAPTER 2 How are allotropes different from isotopes? Allotropes refer to differences in physical form of a macroscopic sample of an element. Isotopes refer to differences between individual atoms of an element. 30 Give an example of each of the following: (a) a monatomic cation: Many possibilities: Na +, Ba 2+, Fe 3+, etc. (b) a monatomic anion: Many possibilities: Cl, O 2, etc. (c) a polyatomic cation: NH 4 +, Hg 2 2+ (d) a polyatomic anion: Many possibilities: NO 3, SO 4 2, PO 4 3, etc. 33 Elements: N 2, S 8, H 2 Compounds: NH 3, NO, CO, CO 2, SO 2 35 Ion Na + Ca 2+ Al 3+ Fe 2+ I F S 2 O 2 N 3 No. protons 11 20 13 26 53 9 16 8 7 No. electrons 10 18 10 24 54 10 18 10 10 38 The molecular formula shows the exact number of atoms of each element in the smallest unit of a substance (a molecule), while an empirical formula indicates the simplest whole-number ratio of each element in a substance. What are similarities and differences between empirical formula ad molecular formula? They are similar in that the ratio of one element to another is the same in either formula for a given substance, while they are different in that the empirical formula will not necessarily indicate the actual number of atoms of the elements in a substance. 40 What does P 4 signify? The formula P 4 signifies a molecule that contains 4 phosphorous atoms. How does it differ from 4 P? The term 4P indicates four individual, unbonded phosphorous atoms. 41 What is an ionic compound? An ionic compound is composed of cations and anions held together by electrostatic attraction. How is electrical neutrality maintained in an ionic compound? Charge neutrality is maintained by having ions present in the reverse ratio of the magnitude of their charges. 43 What are the empirical formulas of the following compounds? (a) C 2 N 2 CN (b) C 6 H 6 CH (c) C 9 H 20 C 9 H 20 (d) P 4 O 10 P 2 O 5 (e) B 2 H 6 BH 3
45 Write the molecular formula of glycine, shown below: SUMMER ASSINGMENT ANSWER KEY: CHAPTER 1 CHAPTER 2 3 In organic compounds, carbon is generally listed first, then hydrogen, then the other elements by increasing atomic number. Thus we have C 2 H 5 NO 2. A more descriptive formula is the structural formula, grouping atoms together by their bonding arrangement: NH 2 CH 2 COOH. 47 Which of the following compounds are likely to be ionic? Which are likely to be molecular? Compounds of metals with nonmetals are usually ionic. Nonmetal-nonmetal compounds are usually molecular. Ionic: LiF, BaCl 2, KCl Molecular: SiCl 4, B 2 H 6, C 2 H 4 49 What is the difference between inorganic and organic compounds? The difference between inorganic compounds and organic compounds is that organic compounds contain carbon in combination with hydrogen, oxygen, nitrogen, and/or sulfur. All other compounds are considered inorganic. 55 (a) KH 2 PO 4 : potassium dihydrogen phosphate (i) PF 5 : phosphorus pentafluoride (b) K 2 HPO 4 : potassium hydrogen phosphate (j) P 4 O 6 : tetraphosphorus hexoxide (c) HBr (gas) : hydrogen bromide (molecular compound) (d) HBr (in water): hydrobromic acid (aqueous solution) (e) Li 2 CO 3 : lithium carbonate (k) CdI 2 : cadmium iodide (f) K 2 C 2 O 7 : potassium dichromate (l) SrSO 4 : strontium sulfate (g) NH 4 NO 2 : ammonium nitrite (m) Al(OH) 3 : aluminum hydroxide (h) HIO 3 : iodic acid 56 (a) KClO: This is an ionic compound in which the metal cation (K + ) has only one charge. The correct name is potassium hypochlorite. Hypochlorite is a polyatomic ion with one less O atom than the chlorite ion, ClO 2 (b) Ag 2 CO 3 : silver carbonate. Silver can form only the +1 ion, so the Roman numeral is not needed. Other single-charge transition metals are Cd and Zn, forming the 2+ ions Cd 2+ and Zn 2+. (c) HNO 2 : This is an oxoacid that contains the nitrite ion, NO 2. The -ite suffix is changed to -ous. The correct name is nitrous acid. (d) KMnO 4 : potassium permanganate (e) CsClO 3 : cesium chlorate
4 SUMMER ASSINGMENT ANSWER KEY: CHAPTER 2 (f) KNH 4 SO 4 : potassium ammonium sulfate (g) FeO: This is an ionic compound in which the metal can form more than one cation. Use a Roman numeral to specify the charge of the Fe ion. Since the oxide ion has a 2 charge, the Fe ion has a +2 charge. The correct name is iron(ii) oxide. (h) Fe 2 O 3 : iron(iii) oxide (i) TiCl 4 : This is an ionic compound in which the metal can form more than one cation. Use a Roman numeral to specify the charge of the Ti ion. Since each of the four chloride ions has a 1 charge (total of 4), the Ti ion has a +4 charge. The correct name is titanium(iv) chloride. (j) NaH: sodium hydride (k) Li 3 N: lithium nitride (l) Na 2 O: sodium oxide (m) Na 2 O 2 : This is an ionic compound in which the metal cation (Na + ) has only one charge. The O 2 2 ion is called the peroxide ion. Each oxygen has a 1 charge. You can determine that each oxygen only has a 1 charge, because each of the two Na ions has a +1 charge. Compare this to sodium oxide in part (l). The correct name is sodium peroxide. 57 (a) rubidium nitrite: RbNO 2 (f) potassium dihydrogen phosphate: KH 2 PO 4 (b) potassium sulfide: K 2 S (g) iodine heptafluoride: IF 7 (c) sodium hydrogen sulfide: NaHS (h) ammonium sulfate: (NH 4 ) 2 SO 4 (d) magnesium phosphate: Mg 3 (PO 4 ) 2 (i) silver perchlorate: AgClO 4 (e) calcium hydrogen phosphate: CaHPO 4 (j) boron trichloride: BCl 3 58 (a) copper(i) cyanide: The Roman numeral I tells you that the Cu cation has a +1 charge. Cyanide has a 1 charge. Since, the charges are numerically equal, no subscripts are necessary in the formula. The correct formula is CuCN. (b) strontium chlorite: Strontium is an alkaline earth metal. It only forms a +2 cation. The polyatomic ion chlorite, ClO 2, has a 1 charge. Since the charges on the cation and anion are numerically different, the subscript of the cation is numerically equal to the charge on the anion, and the subscript of the anion is numerically equal to the charge on the cation. The correct formula is Sr(ClO 2 ) 2. (c) perbromic acid: Perbromic tells you that the anion of this oxoacid is perbromate, BrO 4. The correct formula is HBrO 4 (aq). Remember that (aq) means that the substance is dissolved in water. (d) hydroiodic acid: Hydroiodic tells you that the anion of this binary acid is iodide, I. The correct formula is HI(aq). (e) disodium ammonium phosphate: Na is an alkali metal. It only forms a +1 cation. The polyatomic ion ammonium, NH 4 +, has a +1 charge and the polyatomic ion phosphate, PO 4 3, has a 3 charge. To balance the charge, you need 2 Na + cations. The correct formula is Na 2 (NH 4 )PO 4. (f) lead(ii) carbonate: The Roman numeral II tells you that the Pb cation has a +2 charge. The polyatomic ion carbonate, CO 3 2, has a 2 charge. Since, the charges are numerically equal, no subscripts are necessary in the formula. The correct formula is PbCO 3. (g) tin(ii) fluoride: The Roman numeral II tells you that the Sn cation has a +2 charge. Fluoride has a 1 charge. Since the charges on the cation and anion are numerically different, the
SUMMER ASSINGMENT ANSWER KEY: CHAPTER 1 CHAPTER 2 5 subscript of the cation is numerically equal to the charge on the anion, and the subscript of the anion is numerically equal to the charge on the cation. The correct formula is SnF 2. (h) tetraphosphorous decasulfide: This is a molecular compound. The Greek prefixes tell you the number of each type of atom in the molecule. The correct formula is P 4 S 10. (i) mercury(ii) oxide: The Roman numeral II tells you that the Hg cation has a +2 charge. Oxide has a 2 charge. Since, the charges are numerically equal, no subscripts are necessary in the formula. The correct formula is HgO. (j) mercury(i) iodide: The Roman numeral I tells you that the Hg cation has a +1 charge. However, this cation exists as Hg 2 2+. Iodide has a 1 charge. You need two iodide ion to balance the +2 charge of Hg 2 2+. The correct formula is Hg 2 I 2. (k) selenium hexafluoride: This is a molecular compound. The Greek prefixes tell you the number of each type of atom in the molecule. The correct formula is SeF 6. 60 Which one in each pair resembles each other most closely in chemical properties? a)!! H and 1 1H + b) 14 7 N and 14 7 N 3 c) 12 6C and 13 6 C Changing the electrical charge of an atom usually has a major effect on its chemical properties The two electrically neutral carbon isotopes should have nearly identical chemical properties. 61 One isotope of a metallic element has mass number 65 and 35 neutrons in the nucleus. The cation derived from the isotope has 28 electrons. Write the symbol for this cation. The number of protons = 65 35 = 30. The element that contains 30 protons is zinc, Zn. There are two fewer electrons than protons, so the charge of the cation is +2. The symbol for this cation is Zn 2+. 64 What is wrong with or ambiguous about the phrase four molecules of NaCl? NaCl is an ionic compound; it doesn t form molecules. 67 What is wrong with the name in parentheses? (a) BaCl 2 (barium dichloride) This is an ionic compound. Prefixes are not used. The correct name is barium chloride. (b) Fe 2 O 3 [iron(ii) oxide] Iron has a +3 charge in this compound. The correct name is iron(iii) oxide. (c) CsNO 2 (cesium nitrate) NO 2 is the nitrite ion. The correct name is cesium nitrite. (d) Mg(HCO 3 ) 2 [magnesium(ii) bicarbonate] Magnesium is an alkaline earth metal, which always has a +2 charge in ionic compounds. The Roman numeral is not necessary. The correct name is magnesium bicarbonate. Note: bicarbonate is the old nomenclature. Modern nomenclature would be magnesium hydrogen carbonate. 69 Fill in the blanks in the following table: Symbol 11 5B 26 Fe 2+ 15P 79Au 86 Rn Protons 5 26 15 79 86 Neutrons 6 28 16 117 136 Electrons 5 24 18 79 86 Net Charge 0 +2 3 0 0 71 Write the formula of the common ion derived from each of the following:
6 SUMMER ASSINGMENT ANSWER KEY: CHAPTER 2 (a) Li +, alkali metals always have a +1 charge in ionic compounds (b) S 2 (c) I, halogens have a 1 charge in ionic compounds (d) N 3 (e) Al 3+, aluminum always has a +3 charge in ionic compounds (f) Cs +, alkali metals always have a +1 charge in ionic compounds (g) Mg 2+, alkaline earth metals always have a +2 charge in ionic compounds. 87 alkali metals alkaline earth metals halogens noble gases 1A 2A 3A 4A 5A 6A 7A 8A The metalloids are shown in gray.