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Ch 3. Molecules, Compounds, and Chemical Equations No change occurs inside a nucleus in chemistry Atoms can lose or gain electrons Na − e− → Na+ positive ion = cation Mg − 2e− → Mg2+ Cl + e− → Cl− O + 2e− → O2− negative ion = anion positive ions + negative ions ionic compound The attraction between positive ions and negative ions is called ionic bond. Green: Cl−, Purple: Na+ Atoms can combine together by sharing electrons Covalent bond Different elements combined by covalent bonds Covalent compound Molecule is a group of atoms held together by covalent bonds. Three kinds of chemical formulae to represent a covalent compound Molecular formula Structural formula Empirical formula metals: tend to lose electrons nonmetals: tend to gain electrons metal + nonmetal → ionic compound nonmetal + nonmetal → covalent compound Row: period Column: group Elements in the same group have similar chemical properties. Remember these properties Group 1A (alkali metals) form cations with ONE positive charge. Group 2A (alkaline earth metals) form cations with TWO positive charge. Group 7A (halogens) form anions with ONE negative charge. Group 8A (noble gases) usually do not form compounds. Other common ions to remember: Al3+, Zn2+, Ag+, Cd2+, Sc3+, O2−, S2−, P3−, N3− Review Problem Set 2 How to write chemical formulae for ionic compounds? 1) Write positive ion first, then negative ion. No “+” or “−” in a formula. 2) Subscripts are determined by balancing the charge. number of positive charge = number of negative charge 3) When subscript is 1, no need to specify. NOMENCLATURE Ionic Compounds Binary Ionic Compounds two kinds of elements Naming for Ions Type I: fixed charge (remember them) Cations Type II: different charge Naming for Ions Type I: fixed charge (remember them) Cations Type II: different charge Type I: Same name as the metal Naming for Ions Type I: fixed charge (remember them) Cations Type II: different charge (mostly transition metals) Naming for Ions Type I: fixed charge (remember them) Cations Type II: different charge (mostly transition metals) Type I: Same name as the metal Type II: Same name as the metal (charge in roman number) Naming for Ions Cations: done Anions: add –ide to element’s base name Remember them Naming for Ionic Compounds Compound name = Cation name + Anion name Exercises on Page 131 KF PbI2 SrBr2 SnCl4 Mg3N2 SnO Names → formulae Calcium sulfide Lithium nitride Mercury (II) oxide Aluminum chloride Manganese (IV) oxide Iron (III) oxide NOMENCLATURE Binary Ionic Compounds Ionic Compounds with Polyatomic Ions Naming for Ionic Compounds Compound name = Cation name + Anion name Exercises on Page 131 Ba(OH)2 CuNO2 NH4I NaBrO4 Pb(C2H3O2)2 Problems Set 3 Naming of ionic compounds 1 mol = 6.022 x 1023 particles mass in grams molar mass moles Unit: g/mol molar mass and Avogadro’s number are exact numbers CaCl2 a) Calculate the molar mass of CaCl2. A sample of CaCl2 is 2.86 g. b) How many moles of CaCl2 , Ca2+, and Cl− are in this sample? How many Ca2+, and Cl− ions are in this sample? c) What is the mass of Ca2+ in this sample? What is the mass of Cl− in this sample? 1 mol = 6.022 x 1023 particles molar mass mass in grams moles Two ways to describe the composition of a compound Chemical formula Mass percent of each element mass of component mass percent 100 % mass of whole sample mass of component mass percent 100 % mass of whole sample CaCl2 Calculate the mass percent of Ca and Cl. Pick exactly 1 mol of compound to calculate mass percent. molar mass mass in grams moles mass of component mass percent 100 % mass of whole sample What is the mass percent of nitrogen in ammonium nitrate? mass of component mass percent 100 % mass of whole sample What is the mass percent of nitrogen in ammonium nitrate? NH4NO3 Review Problem Set 3 NOMENCLATURE Binary Ionic Compounds Ionic Compounds with Polyatomic Ions Binary Covalent Compounds Remember these Prefixes • • • • • 1 = mono2 = di3 = tri4 = tetra5 = penta- • • • • • 6 = hexa7 = hepta8 = octa9 = nona10 = deca- Binary Covalent Compounds nonmetal-nonmetal 1. The first element in the formula is named first, using the element name. 2. The second element is named as if it were an anion. 3. Prefixes are used to denote the number of atoms present. 4. The prefix mono- is never used for naming the first element. 5. Drop the final o or a of the prefix when the element begins with a vowel. Examples: page 101-102, 131 NI3 PCl5 CO2 SnCl4 P4S10 a. phosphorus trichloride b. chlorine monoxide c. disulfur tetrafluoride d. phosphorus pentafluoride CO H2O — water NH3 — ammonia NOMENCLATURE Binary Ionic Compounds Ionic Compounds with Polyatomic Ions Binary Covalent Compounds Acids What is an acid? An acid is a compound that releases hydrogen ions (H+) when dissolved in water. HCl → H+ + Cl− HClO3 → H+ + ClO3− dissolved in water = aqueous = aq HCl(aq), HClO3(aq) Binary acids: H and another element Acids Oxyacids: Anions (oxyanion) contain an element and oxygen HCl → H+ + Cl− HClO3 → H+ + ClO3− Binary Acids General formula: HnXm Rules: Start with prefix: hydro Use element root name of anion Add -ic at the end Add the word acid Example: HF(aq), HCl(aq), HBr(aq), HI(aq), H2S(aq) Oxyacids General formula: HnXmOp Rules: Use base name of oxyanion, change ending as follows: change –ate to –ic; change –ite to –ous. Add the word acid Use base name of oxyanion change –ate to –ic; change –ite to –ous. Problems Set 4 Naming of compounds Classification of Matter Homogeneous (Solutions) (visibly indistinguishable) Mixtures (multiple components) Heterogeneous (visibly distinguishable) Matter Elements Pure Substances (one component) Ionic Compounds Covalent Review Problem Set 4 1 mol = 6.022 x 1023 particles mass in grams molar mass moles Unit: g/mol molar mass and Avogadro’s number are exact numbers N2O3 sample: 8.56 g 1 mol = 6.022 x 1023 particles molar mass a)Calculate the molar mass of N2O3. b)How many moles of N2O3 are in this sample? c)How many moles of N are in this sample? d)How many moles of O are in this sample? e)How many N2O3 molecules are in this sample? f)How many N atoms are in this sample? g)How many O atoms are in this sample? h)What is the mass percent of N in N2O3? mass in grams moles Problem Set 5 Two ways to describe the composition of a compound Chemical formula Mass percent of each element mass of component mass percent 100 % mass of whole sample A laboratory analysis of a compound determined the following mass percent: 30.45 % N and 69.55 % O. What is its chemical formula? mass in grams of element molar mass of element moles of element Pick exactly 100 g of compound to calculate. A laboratory analysis of a compound determined the following mass percent: 30.45 % N and 69.55 % O. What is its chemical formula? mass in grams of element molar mass of element moles of element Pick exactly 100 g of compound to calculate. If the molar mass of this compound is 92.02 g/mol, what is its molecular formula? Review Problem Set 5 Example 3.18 on page 115 A laboratory analysis of aspirin determined the following mass Percent: 60.00 % C, 4.48 % H and 35.52 % O. What is its empirical formula? mass in grams of element molar mass of element moles of element Pick exactly 100 g of compound to calculate. If the molar mass of this compound is 180.154 g/mol, what is its molecular formula? Conversion to simplest integer ratio 1.000 : 2.002 : 2.998 = 1: 2 : 3 1.000 : 2.499 : 3.001 = 1: 2.5 : 3 = 10 : 25 : 30 = 2 : 5 : 6 1.0 : 2.4 : 3.0 = 10 : 24 : 30 = 5 : 12 : 15 In a chemical reaction, Old chemical bonds are broken and new chemical bonds are formed. Atoms are neither created nor destroyed. Mass is conserved. Example: A−B + C−D → A−C + B−D Chemical Equation: Reactants → Products CH4 + 2 O2 → CO2 + 2 H2O Each chemical has a certain composition (formula). We must balance each chemical equation. CH4 + 2O2 → CO2 + 2H2O CH4 + 2O2 → CO2 + 2H2O Specify the physical states of the reactants and products s — solid, l — liquid, g — gas, aq — in aqueous solution CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g) How to balance a chemical equation? 1) Start from the most complicated chemical, adjust the coefficients of others. 2) Make all coefficients to simplest integers. Examples C2H5OH (l) + O2 (g) → CO2 (g) + H2O (g) C6H12O6 (s) + O2 (g) → CO2 (g) + H2O (g) Fe2S3 (s) + HCl (aq) → FeCl3 (aq) + H2S (g) NH3 (g) + O2 (g) → NO (g) + H2O (g) Problem Set 6