University:
Missouri State University
Course:
CHM 160 | General Chemistry I
Academic year:

2022
Views:

444

Pages:

16
Author:

Nehemiah Rojas

Section 9.5: The Laws Governing Formulas and Names Read pages 274-279 The Laws Governing Formulas and Names 116   The rules for naming and writing formulas are possible because elements form compounds in predictable ways. Two Important Laws  The Law of Definite Proportions  The Law of Multiple Proportions The Law of Definite Proportions 117 States that in samples of any chemical compound, the masses of the elements are always in the same proportions.  So what does that mean?  Law of Definite Proportions Continued 118  Water  What is the formula for water? H2O  What is the atomic mass of Oxygen? 16.00  What is the atomic mass of Hydrogen? 1.00  What is the mass ratio of Oxygen to Hydrogen in water? 16:2 which reduces to 8:1   Hydrogen Peroxide Dihydrogen Dioxide What is the formula for hydrogen peroxide?  H2O2  What is the mass ratio of Oxygen to Hydrogen in water? 32:2 which reduces to 16:1  Regardless of how much you have, the ratio of masses is always the same! Both water and hydrogen peroxide are composed of hydrogen and oxygen…. 119 But they have different properties. Law of Multiple Proportions 120  Whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers. Two Compounds (X and Y) contain equal masses of Element B. The ratio of the masses of Element A in these compounds is 5:10 or 1:2. Main Idea: 121 In any chemical compound, the elements are always in the same proportion by MASS.  Guidelines for Writing the Chemical Formula of a Compound 122 1. 2. 3. 4. An –ide ending generally indicates a binary compound. An –ite or –ate ending means a polyatomic ion that contains oxygen is in the formula. Prefixes in a name generally indicate that the compound is molecular. A Roman numeral after the name of a cation shows the charge of the cation. Naming Review 123 H in front of the formula? It’s an acid! OH in the formula? It’s a base! (Ionic name) Metal present? It’s ionic! 1. 2. 3. 1. 4. Check to see if you have a transition metal with multiple charges. Only nonmetals? It’s covalent! Naming Practice 124 Formula Name Sodium chloride BrF3 LiNO3 Dinitrogen tetrahydride Potassium hydroxide Rb2O Hydrofluoric acid Ionic or Molecular? Naming Practice Answers 125 Formula Name Ionic or Molecular? NaCl Sodium chloride Ionic BrF3 Bromine trifluoride Molecular LiNO3 Lithium nitrate Ionic N2H4 Dinitrogen tetrahydride Molecular KOH Potassium hydroxide Ionic Rb2O Rubidium oxide Ionic HF Hydrofluoric acid Ionic What’s Next? 126  Book Work Page 279 (#35, 39-41) #35 – What two laws describe how chemical compounds form? 127 The Law of Definite Proportions  The Law of Multiple Proportions  #39 – Name these compounds: 128 a. b. c. CaCO3 PbCrO4 SnCr2O7 a. b. c. Calcium carbonate Lead (II) chromate Tin (II) dichromate #40 – Write the formulas for these compounds: 129 a. Tin (II) hydroxide Sn(OH)2 b. Barium Fluoride BaF2 #40 – Identify the incorrect names or formulas. 130 a. b. c. d. Calcium (II) oxide Aluminum oxide Na2C2O4 Mg(NH4)2