2 | 1 Chapter 2 Atoms, Molecules, and Ions

2 | 2 Postulates of Dalton’s Atomic Theory All matter is composed of indivisible atoms. An atom is an extremely small particle of matter that retains its identity during chemical reactions. An element is a type of matter composed of only one kind of atom.

2 | 3 A compound is a type of matter composed of atoms of two or more elements chemically combined in fixed proportions. A chemical reaction involves the rearrangement of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the reaction.

2 | 4 Atomic Symbol A one- or two-letter notation used to represent an atom corresponding to a particular element. The first letter must be UPPERCASE. The second letter, when present, must be lowercase. Symbols come from the element name; several names come from Latin.

2 | 5 Law of Multiple Proportions When two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in small, whole-number ratios.

2 | 6 As an example, compare the mass of oxygen in the two oxygen compounds of carbon: Carbon monoxide12 g C16 g O Carbon dioxide12 g C32 g O The ratio of oxygen in CO 2 to CO:

? 2 | 7 Like Dalton, today’s chemists model atoms using spheres. Modern models are often drawn using computer programs and use different colors to represent atoms of different elements. Which of these models depicts CO 2 ? ABCDEABCDE E is CO 2

2 | 8 Structure of the Atom The atom is composed of two parts: Nucleus Central core Positively charged Contains most of the atom’s mass Electrons Very light Negatively charged Exist in the region around the nucleus

2 | 9 Discovery of the Electron J. J. Thomson used an apparatus similar to the one shown on the next slide, a cathode ray tube. He discovered that the particles that make up the cathode ray are negative and are part of all matter. This finding is illustrated on the following slides. As a result, Thomson concluded that atoms are not indivisible, as Dalton had postulated.

2 | 10 Cathode Ray Tube

2 | 11 Cathode rays are attracted to the positive end of the magnet and repelled by the negative end.

2 | 12 Thomson’s experiments allowed him to calculate the ratio of the electron’s mass to its charge. Robert Millikan calculated the charge on the electron. He determined the charge on various drops of oil and found the smallest increment in charge—that is, the charge on the electron. This is illustrated on the next slide.

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2 | 14 Nuclear Model of the Atom Experiments done in Ernest Rutherford’s laboratory used positively charged alpha particles to bombard very thin gold (and other metals) foil. Most alpha particles passed through the foil, but a few were scattered at large angles, sometimes almost straight backward. Based on these findings, Rutherford proposed that 99.95% of the atom’s mass is in the positively charged nucleus.

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2 | 17 Proton A nuclear particle having a positive charge equal to that of the electron and a mass more than 1800 times that of the electron. The number of protons in an atom is called the atomic number, Z. An element is a substance whose atoms have the same number of protons and thus the same atomic number, Z.

2 | 18 Neutron A nuclear particle having a mass almost equal to that of the proton but no electrical charge The mass number, A, is the total number of protons and neutrons in the nucleus. Isotopes are atoms whose nuclei have the same atomic number (number of protons) but different numbers of neutrons (mass number).

2 | 19 Nuclide An atom characterized by a certain atomic number, Z, and mass number, A. Nuclide symbol Examples:

? 2 | 20 Write the nuclide symbol for the atom that has 19 protons and 20 neutrons. Atomic number: Z = 19 The element is potassium, K. Mass number: A = = 39 The nuclide symbol is

2 | 21 Atomic Mass The average atomic mass for the naturally occurring element expressed in atomic mass units (amu). Atomic Mass Unit Equal to exactly one-twelfth the mass of a carbon- 12 atom

? 2 | 22 An element has four naturally occurring isotopes. The mass and percentage of each isotope are as follows: Percentage AbundanceMass (amu) What is the atomic weight and name of the element?

2 | 23 To find the portion of the atomic weight due to each isotope, multiply the fraction by the mass of the isotope. The atomic weight is the sum of these products. Fractional Abundance Mass (amu)Mass From Isotope The atomic weight is 207 amu; the element is lead.

2 | 24 Periodic Table of the Elements A tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements.

2 | 25 A period consists of the elements in one horizontal row. A group consists of the elements in one vertical column. Groups are numbered using two systems: IUPAC Numbers 1 through 18 Older systemRoman numerals I–VIII and the letters A and B

2 | 26 Metal A substance or mixture that has a characteristic luster or shine and is generally a good conductor of heat and electricity. Nonmetal An element that does not exhibit the characteristics of a metal Metalloid An element having characteristics of both metals and nonmetals

2 | 27 Chemical Formula A notation that uses atomic symbols with numerical subscripts to convey the relative proportions of atoms of the different elements in the substance.

2 | 28 Molecule A definite group of atoms that are chemically bonded together (tightly connected by attractive forces). Molecular Formula A formula giving the exact number of different atoms of an element in a molecule.

2 | 29 Polymer A very large molecule that is made up of a number of smaller molecules repeatedly linked together. Monomers The small molecules that are linked together to form a polymer.

2 | 30 An ion is an electrically charged particle obtained from an atom or chemically bonded group of atoms by adding or removing one or more electrons. A cation is a positively charged ion formed by losing one or more electrons. A cation is named by its element name followed by the word ion. For example, Na+ is the sodium ion, etc. Under the definition of anion add the following: An anion is named by changing the last part of the element name to –ide followed by the word ion. For example, F- is the fluoride ion, O2- is the oxide ion, N3- is the nitride ion, etc. An anion is a negatively charged ion formed by gaining one or more electrons.

2 | 31 An ionic compound is composed of cations and anions. Ions are arranged in a repeating three-dimensional pattern, forming a crystal. The formula of an ionic compound gives the smallest possible integer number of ions in the substance (without writing charges) so that the combination is electrically neutral. The formula gives the formula unit of the compounds. A formula unit is not a molecule!

? 2 | 32 What is formula of the ionic compound of Mg 2+ and N 3- ? The common multiple of the charges is 6, so we need three Mg 2+ and two N 3-. The resulting formula is Mg 3 N 2

? 2 | 33 What is the formula of the ionic compound of Ca 2+ and PO 4 3- ? The common multiple of the charges is 6, so we need three Ca 2+ and two PO The resulting formula is Ca 3 (PO 4 ) 2

2 | 34 Organic Compounds An important class of molecular substances; they contain carbon combined with other elements – notably hydrogen, oxygen, and nitrogen. Hydrocarbons contain only carbon and hydrogen.

2 | 35 A functional group is a reactive portion of a molecule that undergoes predictable reactions. ExamplesName of Group Functional Group Methyl alcoholAlcohol Dimethyl etherEther Acetic acidCarboxylic acid

2 | 36 Chemical nomenclature is the systematic naming of chemical compounds. Compounds that are not organic are called inorganic compounds. Carbon monoxide, carbon dioxide, carbonates, and cyanides are also classified as inorganic compounds.

2 | 37 Naming Inorganic Compounds 1.The cation is always named first with the name of the cation without the word ion. 2.The anion is named second with the name of the anion without the word ion. 3.Examples: CationAnionName Na + Br - Sodium bromide Mg 2- O 2- Magnesium oxide Al 3+ Cl - Aluminum chloride

2 | 38 Monatomic ions Ions formed from a single atom. Common monatomic ions are listed on the next slide by group and by period.

2 | 39 Common Monatomic Ions of the Main-Group Elements Bi 3+ Pb 2+ Tl 3+, Tl + Ba 2+ Cs + I-I- Te 2- Sn 2+ In 3+ Sr 2+ Rb + Br - Se 2- Ga 3+ Ca 2+ K+K+ Cl - S 2- Al 3+ Mg 2+ Na + F-F- O 2- N 3- Be 2+ Li + H-H VIIAVIAVAIVAIIIAIIAIA Period

2 | 40 Rules for Predicting the Charge on a Monatomic Ion 1.Most main-group metals have one monatomic ions with a charge equal to the group number. Al, in Group IIIA(3), has one ion, Al 3+. Sr, in Group IIA(2), has one ion, Sr 2+. K, in Group IA(1), has one ion, K +.

2 | 41 2.Some main-group metals with high atomic number have more than one cation. One cation will have the charge of the group number minus 2; the second cation will have a charge equal to the group number Pb in Group IVA(14) has two ions: Pb 2+ and Pb 4+ Tl in Group IIIA(13) has two ions: Tl + and Tl 3+

2 | 42 3.Most transition metals form more than one cation, of which one is +2. Zn and Cd form only the +2 ion. Ag forms only the +1 ion. 4.Nonmetal main-group elements form one monatomic anion with a charge equal to the group number minus 8. F in Group VIIA(17) forms the F - ion. S in Group VIA(16) forms the S 2- ion. N in Group VA(15) forms the N 3- ion.

2 | 43 Naming Monatomic Ions Monatomic cations are named after the element if the element forms only one cation.

2 | 44 If more than one cation forms: a.In the Stock system, the charge is written using a Roman numeral and is enclosed in parentheses. Cu 2+ is copper(II). Cu + is copper(I). b.In an older system, the suffic –ic (for the higher-charged cation) or –ous for the lower-charged cation) is added to the element’s stem. Cu 2+ is cupric. Cu + is cuprous.

2 | 45 Fe 3+ is iron(III) or ferric ion. Fe 2+ is iron(II) or ferrous ion. Hg 2+ is mercury(II) or mercuric ion. The second ion mercury forms is diatomic: Hg 2 2+ is mercury(I) or mercurous ion.

2 | 46 Cr 3+ is chromium(III) or chromic ion. Cr 2+ is chromium(II) or chromous ion. Mn 2+ is manganese(II) or manganous ion. Co 2+ is cobalt(II) or cobaltous ion. Zinc forms only Zn 2+, so it is called zinc ion. Cadmium forms only Cd 2+, so it is called cadmium ion. Silver forms only Ag +, so it is called silver ion.

2 | 47 Polyatomic Ion An ion consisting of two or more atoms chemically bonded together and carrying an electrical charge. Table 2.5 lists common polyatomic ions.

2 | 48 Cations mercury(I) or mercurousHg 2 2+ ammoniumNH 4 + Anions peroxideO 2 - hydroxideOH - cyanideCN -

2 | 49 phosphatePO 4 3- monohydrogen phosphateHPO 4 2- dihydrogen phosphateH 2 PO 4 - carbonateCO 3 2- hydrogen carbonate (bicarbonate)HCO 3 - sulfateSO 4 2- hydrogen sulfate (bisulfate)HSO 4 - sulfiteSO 3 2- hydrogen sulfite (bisulfite)HSO 3 -

2 | 50 acetateC 2 H 3 O 2 - oxalateC 2 O 4 2- chromateCrO 4 2- dichromateCr 2 O 7 2- permanganateMnO 4 - nitrateNO 3 - nitriteNO 2 -

2 | 51 hypochloriteClO - chloriteClO 2 - chlorateClO 3 - perchlorateClO 4 -

? 2 | 52 What are the names of the following ionic compounds? BaO Cr 2 (SO 4 ) 3 BaO is barium oxide. Cr 2 (SO 4 ) 3 is chromium(III) sulfate or chromic sulfate.

? 2 | 53 What are the chemical formulas for the following ionic compounds? potassium carbonate manganese(II) sulfate The ions K + and CO 3 2- form K 2 CO 3 The ions Mn 2+ and SO 4 2- form MnSO 4

2 | 54 Binary Molecular Compounds A compound composed of only two elements. Binary compound of a metal and a nonmetal are generally named using ionic rules.

2 | 55 Naming Binary Molecular Compounds We usually name the elements in the order given in the formula. Name the first element using the element name. Name the second element using the element root + -ide suffix.

2 | 56 Add a prefix to each name to indicate the number of atoms of that element. The prefix mono- is used only when needed to distinguish two compounds of the same two elements. The final vowel of the prefix is often dropped when followed by an element name that begins with a vowel. Oxygen is the most common example. N 2 O 4 dinitrogen tetroxide (“a” is dropped) NO nitrogen monoxide(only one “o”) (also called nitric oxide)

2 | 57 Prefixes (Greek) One (1)mono- Two (2)di- Three (3)tri- Four (4)tetra- Five (5)penta- Six (6)hexa- Seven (7)hepta- Eight (8)octa- Nine (9)nona- Ten (10)deca-

2 | 58 Some compounds have common names that differ from their systematic names: H 2 Shydrogen sulfide (the “di” is omitted) H 2 Owater NH 3 ammonia Common names need to be memorized.

2 | 59 Acids and Corresponding Anions Oxoacids contain hydrogen, oxygen, and a third central atom. To name an acid from its anion name: 1.Change an –ate suffix to –ic. 2.Change an –ite suffix to –ous. 3.Add the word “acid.”” For example: HNO 3 nitric acid H 2 SO 4 sulfuric acid

2 | 60 sulfuric acid H 2 SO 4 sulfate ionSO 4 2- sulfurous acid H 2 SO 3 sulfite ionSO 3 2- phosphoric acid H 3 PO 4 phosphate ionPO 4 3- nitric acidHNO 3 nitrate ionNO 3 - nitrous acid HNO 2 nitrite ionNO 2 - carbonic acid H 2 CO 3 carbonate ion CO 3 2- OxoacidOxoanion

2 | 61 hypochlorous acid HClOhypochlorite ion ClO - chlorous acid HClO 2 chlorite ion ClO 2 - chloric acid HClO 3 chlorate ion ClO 3 - perchloric acid HClO 4 perchlorate ion ClO 4 - Oxoacid Oxoanion

? 2 | 62 What are the names of the following compounds? OF 2 S 4 N 4 BCl 3 OF 2 is oxygen difluoride S 4 N 4 is tetrasulfur tetranitride BCl 3 is boron trichloride

? 2 | 63 What are the formulas for the following binary molecular compounds? carbon disulfide nitrogen tribromide dinitrogen tetrafluoride The formula for carbon disulfide is CS 2. The formula for dinitrogen tetrafluoride is N 2 F 4. The formula for nitrogen tribromide is NBr 3.

? 2 | 64 Bromine has an oxoacid, HBrO 2, bromous acid (compare to HClO 2, chlorous acid). What are the name and formula of the corresponding anion? The anion corresponding to HBrO 2 is bromite, BrO 2 -.

2 | 65 Hydrate A compound that contains water molecules weakly bound in the crystals. The formula of a hydrate is written with a dot before the water molecule(s) included. For example: CuSO 4  5H 2 O

2 | 66 Hydrates are named using the anhydrous (without water) compound name followed by the prefix for the number of water molecules included and the word “hydrate.” For example: CuSO 4  5H 2 O is named copper(II) sulfate pentahydrate.

? 2 | 67 A compound whose common name is green vitriol has the chemical formula FeSO 4  7H 2 O. What is the chemical name of this compound? FeSO 4  7H 2 O is iron(II) sulfate heptahydrate.

? 2 | 68 Calcium chloride hexahydrate is used to melt snow on roads. What is the chemical formula of the compound? The chemical formula for calcium chloride hexahydrate is CaCl 2  6H 2 O.

2 | 69 A chemical equation is the symbolic representation of a chemical reaction in terms of chemical formulas. For example:2Na + Cl 2  2NaCl Reactants are the starting materials; they are written on the left of the equation. Products are the materials at the end of the reaction; they are written on the right of the equation.

2 | 70 Because a reaction must accurately describe the chemical reaction, it must be consistent with the law of conservation of mass. When this is not the case, after correct formulas are written for each reactant and product, the coefficients are adjusted so that the same number of each atom is present in both the reactants and the products. This is called balancing the equation.

2 | 71 For example, the reaction of sodium with chlorine produced sodium chloride. First, we determine the correct formula for each compound. Sodium is Na. Chlorine is Cl 2. Sodium chloride is NaCl.

2 | 72 Second, we write the reaction. Na + Cl 2  NaCl Third, we check the number of each atom on each side of the equation. This equation shows two Cl atoms on the reactant side and only one Cl atom on the product side. To balance the Cl atoms, we insert a coefficient of “2” before NaCl on the product side. Na + Cl 2  2NaCl

2 | 73 Na + Cl 2  2NaCl Now the Na are not balanced: there is one on the reactant side and there are two on the product side. To balance Na, we insert the coefficient “2” before Na on the reactant side. 2Na + Cl 2  2NaCl The reaction is now balanced!

? 2 | 74 Balance the following equation: CS 2 + O 2  CO 2 + SO 2 Tally the number of each atom on each side: C1 on reactant side; 1 on product side S2 on reactant side; 1 on product side O2 on reactant side; 4 on product side Begin by inserting the coefficient “2” before SO 2 on the product side. We leave O 2 until later because it is an element.

2 | 75 CS 2 + O 2  CO 2 + 2SO 2 Tally the atoms again: C1 on reactant side; 1 on product side S2 on reactant side; 2 on product side O2 on reactant side; 6 on product side Insert a “3” before O 2 : CS 2 + 3O 2  CO 2 + 2SO 2

2 | 76 CS 2 + 3O 2  CO 2 + 2SO 2 Tally the atoms again: C1 on reactant side; 1 on product side S2 on reactant side; 2 on product side O6 on reactant side; 6 on product side The reaction is now balanced!

? 2 | 77 Balance the following equation: NH 3 + O 2  NO + H 2 O Tally the number of each atom on each side: N1 on reactant side; 1 on product side H3 on reactant side; 2 on product side O2 on reactant side; 2 on product side Begin by inserting the coefficient “2” before NH 3 on the reactant side and the coefficient “3” before H 2 O on the product side. We leave O 2 until later because it is an element.

2 | 78 2NH 3 + O 2  NO + 3H 2 O Tally the atoms again: N2 on reactant side; 1 on product side H6 on reactant side; 6 on product side O2 on reactant side; 4 on product side To balance N, insert a “2” before NO: 2NH 3 + O 2  2NO + 3H 2 O

2 | 79 2NH 3 + O 2  2NO + 3H 2 O Tally the atoms again: N2 on reactant side; 2 on product side H6 on reactant side; 6 on product side O2 on reactant side; 5 on product side Since this gives us an odd number oxygens, we double the coefficients on NH 3, NO, and H 2 O and to balance O, insert a “5” before O 2.

2 | 80 Tally the atoms again to double check: 4NH 3 + 5O 2  4NO + 6H 2 O N4 on reactant side; 4 on product side H12 on reactant side; 12 on product side O10 on reactant side; 10 on product side The reaction is now balanced!

? 2 | 81 Balance the following equation: C 2 H 5 OH + O 2  CO 2 + H 2 O Tally the number of each atom on each side: C2 on reactant side; 1 on product side H6 on reactant side; 2 on product side O3 on reactant side; 3 on product side Begin by balancing H. Insert the coefficient “3” before H 2 O on the product side. We leave O 2 until later because it is an element.

2 | 82 C 2 H 5 OH + O 2  CO 2 + 3H 2 O Tally the number of each atom on each side: C2 on reactant side; 1 on product side H6 on reactant side; 6 on product side O3 on reactant side; 5 on product side To balance C, insert a “2” before CO 2.

2 | 83 C 2 H 5 OH + O 2  2CO 2 + 3H 2 O Tally the number of each atom on each side: C2 on reactant side; 2 on product side H6 on reactant side; 6 on product side O3 on reactant side; 7 on product side To balance O, insert a “3” before O 2.

2 | 84 C 2 H 5 OH + 3O 2  2CO 2 + 3H 2 O Tally the number of each atom on each side: C2 on reactant side; 2 on product side H6 on reactant side; 6 on product side O7 on reactant side; 7 on product side The reaction is now balanced!