Chapter 2 Atoms, Molecules, and Ions PDF

Chapter 2 (3 Lectures) Fifth Edition Atoms, Molecules, and Ions  CHAPTER 2 Atoms, Molecules, and Ions 2.3 Atomic Number, Mass Number, and Isotopes. 2.4 The Periodic Table. 2.5 The Atomic Mass Scale and Aver...

Chapter 2 (3 Lectures) Fifth Edition Atoms, Molecules, and Ions  CHAPTER 2 Atoms, Molecules, and Ions 2.3 Atomic Number, Mass Number, and Isotopes. 2.4 The Periodic Table. 2.5 The Atomic Mass Scale and Average Atomic Mass. 2.6 Ions and Ionic Compounds. 2.7 Molecules and Molecular Compounds. 2 ©2020 McGraw-Hill Education  2.3 Atomic Number, Mass Number, and Isotopes Topics Atomic Number, Mass Number, and Isotopes Learning Objectives Define atomic number and mass number of an atom. Define and provide examples of isotopes of an element. Write the nuclide symbol of an element. 3 ©2020 McGraw-Hill Education  2.3 Atomic Number, Mass Number, and Isotopes 1 Atomic Number, Mass Number, and Isotopes The atomic number (Z) is the number of protons in the nucleus of each atom of an element. The mass number (A) is the total number of neutrons and protons present in the nucleus of an atom of an element. mass number (A) = number of protons (Z) + number of neutrons 4 ©2020 McGraw-Hill Education  2.3 Atomic Number, Mass Number, and Isotopes 2 Atomic Number, Mass Number, and Isotopes Most elements have two or more isotopes, atoms that have the same atomic number (Z) but different mass numbers (A). 1 2 3 1 H 1 H 1H hydrogen deuterium tritium 5 ©2020 McGraw-Hill Education  2.3 Atomic Number, Mass Number, and Isotopes 3 Atomic Number, Mass Number, and Isotopes 235 238 92 U 92 U 235 – 92 = 143 neutrons 238 – 92 = 146 neutrons 6 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.2 Setup Determine the numbers of protons, neutrons, and electrons in each of the following species:  a  1735 Cl,  b  1737 Cl,  c  41K,and  d  carbon  14 Setup Number of protons = Z, number of neutrons = A – Z, and number of electrons = number of protons. Recall that the 14 in carbon-14 is the mass number. 7 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.2 Solution 1 Solution (a) The atomic number is 17, so there are 17 protons. The mass number is 35, so the number of neutrons is 35 − 17 = 18. The number of electrons equals the number of protons, so there are 17 electrons. 8 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.2 Solution 2 Solution (b) Again, the atomic number is 17, so there are 17 protons. The mass number is 37, so the number of neutrons is 37 − 17 = 20. The number of electrons equals the number of protons, so there are 17 electrons, too. 9 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.2 Solution 3 Solution (c) The atomic number of K (potassium) is 19, so there are 19 protons. The mass number is 41, so there are 41 − 19 = 22 neutrons. There are 19 electrons. (d) Carbon-14 can also be represented as 14C. The atomic number of carbon is 6, so there are 6 protons and 6 electrons. There are 14 − 6 = 8 neutrons. 10 ©2020 McGraw-Hill Education  2.4 The Periodic Table Topics The Periodic Table Learning Objectives Identify periods and groups on the periodic table. Identify the main-group (1A-8A) and transition (1B-8B) elements on the periodic table. Recognize the portions of the periodic table that contain the metals, nonmetals, and metalloids (semimetals). 11 ©2020 McGraw-Hill Education  2.4 The Periodic Table 1 The Periodic Table 12 ©2020 McGraw-Hill Education  2.4 The Periodic Table 2 The Periodic Table Elements are arranged in horizontal rows called periods and in vertical columns called groups or families. Elements in the same group tend to have similar physical and chemical properties. The elements can be categorized as metals, nonmetals, or metalloids. 13 ©2020 McGraw-Hill Education  2.4 The Periodic Table 3 The Periodic Table A metal is a good conductor of heat and electricity, whereas a nonmetal is usually a poor conductor of heat and electricity. A metalloid has properties that are intermediate between those of metals and nonmetals. 14 ©2020 McGraw-Hill Education  2.4 The Periodic Table 15 ©2020 McGraw-Hill Education 15  2.4 The Periodic Table 16 ©2020 McGraw-Hill Education 16  2.4 The Periodic Table The Periodic Table Group 1A: Alkali metals Group 2A : Alkaline metals Group 6A : Chalcogens Group 7A : Halogens Group 8A: Noble gases Group 1B-8B : Transition elements or Transition metals. 17 ©2020 McGraw-Hill Education 17  2.5 The Atomic Mass Scale and Average Atomic Mass Topics The Atomic Mass Scale and Average Atomic Mass Learning Objectives Define atomic mass unit and atomic mass. Determine the atomic mass of an element from the isotopic masses and percent (of fractional) abundances. 18 ©2020 McGraw-Hill Education  2.5 The Atomic Mass Scale and Average Atomic Mass The Periodic Table When you look up the atomic mass of carbon in a table such as the one on the inside front cover of the text, you will find that its value is 12.01 amu, not 12.00 amu. The difference arises because most naturally occurring elements (including carbon) have more than one isotope. The atomic masses in the periodic table are average atomic masses. 19 ©2020 McGraw-Hill Education 19  2.5 The Atomic Mass Scale and Average Atomic Mass 4 The Periodic Table Access the text alternative for these images 20 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.3 Oxygen is the most abundant element in both Earth’s crust and the human body. The atomic masses of its three stable isotopes, 168 O  99.757 percent  , 178 O  0.038 percent  , and 18 8 O  0.205 percent  , are 15.9949, 16.9991, and 17.9992 amu, respectively. Calculate the average atomic mass of oxygen using the relative abundances given in parentheses. Report the result to four significant figures. 21 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.3 Solution Solution  0.99757 15.9949 amu   0.00038 16.9991 amu   0.0020517.9992   16.00 amu 22 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds Topics Atomic Ions Polyatomic Ions Formulas of Ionic Compounds Naming Ionic Compounds Oxoanions Hydrates 23 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 1 Atomic Ions An atomic ion or monatomic ion is one that consists of just one atom with a positive or negative charge. The loss of one or more electrons from an atom yields a cation, an ion with a net positive charge. Na Atom Na+ Ion 11 protons 11 protons 11 electrons 10 electrons 24 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 2 Atomic Ions An anion is an ion whose net charge is negative due to an increase in the number of electrons. Cl Atom Cl− Ion 17 protons 17 protons 17 electrons 18 electrons Sodium chloride (NaCl), ordinary table salt, is called an ionic compound because it consists of cations (Na+) and anions (Cl− ). 25 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 3 Atomic Ions An atom can lose or gain more than one electron. 26 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 4 Atomic Ions Designate different cations with Roman numerals, using the Stock system. Mn2+ : manganese(II) ion Mn3+ : manganese(III) ion Mn4+ :manganese(IV) ion 27 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 6 Atomic Ions A monatomic anion is named by changing the ending of the element’s name to –ide, and adding the word ion. Thus, the anion of chlorine (Cl− ), is called chloride ion. 28 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 7 TABLE 2.3 Common Polyatomic Ions Name - Cations Formula/Charge ammonium NH4+ Polyatomic Ions hydronium Mercury(I) H3O+ Hg22+ Name - Anions Formula/Charge Ions that consist of a acetate azide C2H3O2− N3− combination of two or more chlorate chlorite CIO3− CIO2− atoms are called chromate cyanide CrO42− CN− polyatomic ions. dichromate dihydrogen phosphate Cr2O72− H2PO4− hydrogen carbonate or bicarbonate HCO3− hydrogen phosphate HPO42− hydrogen sulfate or bisulfate HSO4− hydroxide OH− hypochlorite CIO− nitrate NO3− nitrite NO2− perchlorate C2O42− permanganate MnO4− peroxide O22− phosphate PO43− phosphite PO33− sulfate SO42− sulfite SO32− thiocyanate SCN− 29 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 8 Polyatomic Ions Name - Anion Formula/Charge carbonate CO32− chlorate CIO3− chlorite CIO2− chromate CrO42− cyanide CN− dichromate Cr2O72− dihydrogen phosphate H2PO4− hydrogen carbonate or bicarbonate HCO3− hydrogen phosphate HPO42− hydrogen sulfate or bisulfate HSO4− hydroxide OH− hypochlorite CIO− 30 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 9 Polyatomic Ions Name - Anion Formula/Charge nitrate NO3− nitrite NO2− oxalate C2O42− perchlorate CIO4− permanganate MnO4− peroxide O22− phosphate PO43− phosphite PO33− sulfate SO42− sulfite SO32− thiocyanate SCN− 31 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 10 Formulas of Ionic Compounds 32 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 11 Formulas of Ionic Compounds Access the text alternative for these images 33 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 12 Naming Ionic Compounds 34 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.4 Setup Name the following ionic compounds: (a) MgO. (b) Al(OH)3. (c) Fe2(SO4)3. Setup (a) Mg2+ O2–. (b) Al3+ OH–. (c) Since the charge on SO2− 4 is −2, the charge on Fe must be +3: Fe3+. 35 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.4 Solution Name the following ionic compounds: (a) MgO. (b) Al(OH)3. (c) Fe2(SO4)3. Solution (a) magnesium oxide. (b) aluminum hydroxide. (c) iron (III) sulfate. 36 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.5 Setup Deduce the formulas of the following ionic compounds: (a) mercury(I) chloride. (b) lead(II) chromate. (c) potassium hydrogen phosphate. Setup  2 a Hg 2 Cl b Pb 2 CrO 2 4  c K  HPO 2 4 37 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.5 Solution Deduce the formulas of the following ionic compounds: (a) mercury(I) chloride. (b) lead(II) chromate. (c) potassium hydrogen phosphate. Solution  a Hg2Cl2 b  PgCrO4  c  K2HPO4 38 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 13 Oxoanions Oxoanions are polyatomic anions that contain one or more oxygen atoms and one atom (the “central atom”) of another element. Examples include the chlorate       ClO3 , nitrate NO3 , and sulfate SO24 ions. 39 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 14 Oxoanions Starting with the oxoanions whose names end in –ate, we can name these ions as follows: 1. The ion with one more O atom than the –ate ion is called the per... ate ion. Thus, ClO3− is the chlorate ion, so ClO4− is the perchlorate ion. 2. The ion with one less O atom than the –ate anion is called the –ite ion. Thus, ClO2− is the chlorite ion. 40 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 15 Oxoanions Starting with the oxoanions whose names end in –ate, we can name these ions as follows: 3. The ion with two fewer O atoms than the –ate ion is called the hypo... ite ion. Thus, ClO− is the hypochlorite ion. 41 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.6 Setup Name the following species: (a) BrO4−. (b) HCO3−. (c) SO32−. Setup (a) BrO3− is the bromate ion. (b) CO3− is the carbonate ion. (c) SO42− is the sulfate ion. 42 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.6 Solution Name the following species: (a) BrO4−. (b) HCO3−. (c) SO32−. Solution (a) perbromate ion. (b) hydrogen carbonate ion (or bicarbonate ion). (c) sulfite ion. 43 ©2020 McGraw-Hill Education  2.6 Ions and Ionic Compounds 16 Hydrates Hydrates are compounds that have a specific number of water molecules within their solid structure. BaCl2 ∙ 2H2O barium chloride dihydrate LiCl ∙ H2O lithium chloride monohydrate MgSO4 ∙ 7H2O magnesium sulphate heptahydrate Sr(NO3)2 ∙ 4H2O strontium nitrate tetrahydrate 44 ©2020 McGraw-Hill Education McGraw-Hill Education/Charles D. Winters, photographer  2.7 Molecules and Molecular Compounds Topics Molecular Formulas Naming Molecular Compounds Simple Acids Oxoacids Empirical Formulas of Molecular Substances 45 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 1 Molecules A molecule is a combination of at least two atoms in a specific arrangement held together by electrostatic forces known as covalent chemical bonds. The hydrogen molecule, symbolized as H2, is called a diatomic molecule because it contains two atoms. Other elements that normally exist as diatomic molecules are nitrogen (N2), oxygen (O2), and the Group 7A elements—fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2). 46 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 2 Molecules In homonuclear diatomic molecules, both atoms in each molecule are of the same element. A diatomic molecule can also contain atoms of different elements (heteronuclear diatomic molecules). 47 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 4 Molecular Formulas The structural formula shows not only the elemental composition, but also the general arrangement of atoms within the molecule. 48 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.7 Write the molecular formula of ethanol based on its ball- and-stick model, shown here. Access the text alternative for these images 49 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.7 Solution Write the molecular formula of ethanol based on its ball- and-stick model, shown here. Solution C2H6O 50 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 5 Naming Molecular Compounds Binary molecular compounds consist of just two different elements. To name such a compound, we first name the element that appears first in the formula. We then name the second element, changing the ending of its name to –ide. HCl hydrogen chloride SiCsilicon carbide 51 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 6 Naming Molecular Compounds TABLE 2.4 Greek Prefixes. Use Greek prefixes to denote Prefix Meaning the number of atoms of each Mono- 1 element present. Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Nona- 9 Deca- 10 52 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 7 Naming Molecular Compounds TABLE 2.5 Some Compounds Named Using Greek Prefixes. Compound Name CO Carbon monoxide CO2 Carbon dioxide SO2 Sulfur dioxide SO3 Sulfur trioxide NO2 Nitrogen dioxide N2O5 Dinitrogen pentoxide 53 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 8 Naming Molecular Compounds The prefix mono– is generally omitted for the first element. SO2, for example, is named sulfur dioxide, not monosulfur dioxide. For ease of pronunciation, we usually eliminate the last letter of a prefix that ends in “o” or “a” when naming an oxide. Thus, N2O5 is dinitrogen pentoxide, rather than dinitrogen pentaoxide. 54 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.8 Name the following binary molecular compounds: (a) NF3 and (b) N2O4. 55 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.8 Solution Name the following binary molecular compounds: (a) NF3 and (b) N2O4. Solution (a) nitrogen trifluoride and (b) dinitrogen tetroxide. 56 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.9 Write the chemical formulas for the following binary molecular compounds: (a) sulfur tetrafluoride and (b) tetraphosphorus decasulfide. 57 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.9 Solution Write the chemical formulas for the following binary molecular compounds: (a) sulfur tetrafluoride and (b) tetraphosphorus decasulfide. Solution (a) SF4 and (b) P4S10. 58 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 9 Naming Molecular Compounds The names of molecular compounds containing hydrogen do not usually conform to the systematic nomenclature guidelines. B2H6 Diborane PH3 Phosphine SiH4 Silane H2O Water NH3 Ammonia H2S Hydrogen sulfide 59 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 10 Simple Acids Acids make up another important class of molecular compounds. One definition of an acid is a substance that produces hydrogen ions (H+) when dissolved in water. Several binary molecular compounds produce hydrogen ions when dissolved in water and are, therefore, acids. In these cases, two different names can be assigned to the same chemical formula. 60 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 11 Simple Acids For example, HCl, hydrogen chloride, is a gaseous compound. When it is dissolved in water, however, we call it hydrochloric acid. The rules for naming simple acids of this type are as follows: remove the –gen ending from hydrogen (leaving hydro–), change the –ide ending on the second element to –ic, combine the two words, and add the word acid. hydrogen chloride  – ic acid hydrochloric acid 61 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 12 Simple Acids TABLE 2.6 Some Simple Acids. Formula Binary Compound Name Acid Name HF Hydrogen fluoride Hydrofluoric acid HCl Hydrogen chloride Hydrochloric acid HBr Hydrogen bromide Hydrobromic acid HI Hydrogen iodide Hydroiodic acid HCN∗ Hydrogen cyanide Hydrocyanic acid *Although HCN is not a binary compound, it is included in this table because it is similar chemically to HF, HC1, HBr, and HI. 62 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 13 Oxoacids An important class of acids known as oxoacids, which ionize to produce hydrogen ions and the corresponding oxoanions. The formula of an oxoacid can be determined by adding enough H+ ions to the corresponding oxoanion to yield a formula with no net charge. For example, the formulas of oxoacids based on the nitrate (NO3−) and sulfate (SO42−) ions are HNO3 and H2SO4, respectively. 63 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 14 Oxoacids The names of oxoacids are derived from the names of the corresponding oxoanions using the following guidelines: 1. An acid based on an –ate ion is called... ic acid. Thus, HClO3 is called chloric acid. 2. An acid based on an –ite ion is called... ous acid. Thus, HClO2 is called chlorous acid. 64 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 15 Oxoacids The names of oxoacids are derived from the names of the corresponding oxoanions using the following guidelines: 3. Prefixes in oxoanion names are retained in the names of the corresponding oxoacids. Thus, HClO4 and HClO are called perchloric acid and hypochlorous acid, respectively. 65 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 16 Oxoacids Many oxoacids, such as H2SO4 and H3PO4, are polyprotic— meaning that they have more than one ionizable hydrogen atom. In these cases, the names of anions in which one or more (but not all) of the hydrogen ions have been removed must indicate the number of H ions that remain. H3PO4 phosphoric acid HPO42− hydrogen phosphate ion H2PO4− dihydrogen phosphate ion PO43− phosphate ion 66 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.10 Setup Determine the formula of sulfurous acid. Setup The sulfite ion is SO32−. 67 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.10 Solution Determine the formula of sulfurous acid. Solution The formula of sulfurous acid is H2SO3. 68 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 17 Oxoacids Organic compounds contain carbon and hydrogen, sometimes in combination with other elements such as oxygen, nitrogen, sulfur, and the halogens. The simplest organic compounds are those that contain only carbon and hydrogen and are known as hydrocarbons. Among hydrocarbons, the simplest examples are compounds known as alkanes. 69 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 18 TABLE 2.7 Formulas, Names, and Models of Some Simple Alkanes. Formula Name Model CH4 Methane C2H6 Ethane C3H8 Propane C4H10 Butane 70 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 19 Formula Name Model C5H12 Pentane C6H14 Hexane C7H16 Heptane C8H18 Octane 71 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 20 Formula Name Model C9H20 Nonane C10H22 Decane 72 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 21 Oxoacids Many organic compounds are derivatives of alkanes in which one of the H atoms has been replaced by a group of atoms known as a functional group. The functional group determines many of the chemical properties of a compound because it typically is where a chemical reaction occurs. 73 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 22 TABLE 2.8 Organic Functional Groups Name Functional Group Model Alcohol —OH Aldehyde —CHO Carboxylic acid —COOH Amine —NH2 74 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 23 Empirical Formulas of Molecular Substances Molecular substances can also be represented using empirical formulas. The word empirical means “from experience” or, in the context of chemical formulas, “from experiment.” The empirical formula tells what elements are present in a molecule and in what whole-number ratio they are combined. 75 ©2020 McGraw-Hill Education  2.7 Molecules and Molecular Compounds 24 TABLE 2.9 Molecular and Empirical Formula Molecular Empirical Compound Model Model Formula Formula Water H2O H2O Hydrogen H2O2 HO peroxide Ethane C2H6 CH3 Propane C3H8 C3H8 Acetylene C2H2 CH Benzene C6H6 CH 76 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.11 Write the empirical formulas for the following molecules: (a) glucose (C6H12O6). (b) adenine (C5H5N5). (c) nitrous oxide (N2O). 77 ©2020 McGraw-Hill Education  SAMPLE PROBLEM 2.11 Solution Write the empirical formulas for the following molecules: (a) glucose (C6H12O6). (b) adenine (C5H5N5). (c) nitrous oxide (N2O). Solution (a) CH2O. (b) CHN. (c) N2O. 78 ©2020 McGraw-Hill Education