Lecture Notes Alan D. Earhart Southeast Community College Lincoln, NE Chapter 2 Atoms, Molecules, and Ions John E. McMurry Robert C. Fay CHEMISTRY Fifth Edition Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 2/2 Conservation of Mass and the Law of Definite Proportions Law of Conservation of Mass: Mass is neither created nor destroyed in chemical reactions. Hg I 2 (s) + 2KNO 3 (aq)Hg(NO 3 ) 2 (aq) + 2K I(aq) 4.55 g g = 6.57 g Aqueous solutions of mercury(II) nitrate and potassium iodide will react to form a precipitate of mercury(II) iodide and aqueous potassium iodide g g = 6.57 g
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/3 Conservation of Mass and the Law of Definite Proportions Law of Definite Proportions: Different samples of a pure chemical substance always contain the same proportion of elements by mass. By mass, water is:88.8 % oxygen 11.2 % hydrogen
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/4 Dalton’s Atomic Theory and the Law of Multiple Proportions Elements are made up of tiny particles called atoms. Each element is characterized by the mass of its atoms. Atoms of the same element have the same mass, but atoms of different elements have different masses. Chemical combination of elements to make different substances occurs when atoms join together in small whole-number ratios. Chemical reactions only rearrange the way that atoms are combined; the atoms themselves don’t change.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/5 Dalton’s Atomic Theory and the Law of Multiple Proportions Law of Multiple Proportions: Elements can combine in different ways to form different substances, whose mass ratios are small whole-number multiples of each other. 8 grams oxygen per 7 grams nitrogen 16 grams oxygen per 7 grams nitrogen nitric oxide: nitrous oxide:
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/6 Dalton’s Atomic Theory and the Law of Multiple Proportions Law of Multiple Proportions: Elements can combine in different ways to form different substances, whose mass ratios are small whole-number multiples of each other.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/7 The Structure of Atoms: Electrons Cathode-Ray Tubes: J. J. Thomson ( ) proposed that cathode rays must consist of tiny negatively charged particles. We now call them electrons.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/8 The Structure of Atoms: Protons and Neutrons Atomic Nucleus: Ernest Rutherford ( ) bombarded gold foil with alpha particles. Although most of the alpha particles passed through the foil undeflected, approximately 1 in every 20,000 particles were deflected. A fraction of those particles were deflected back at an extreme angle. Rutherford proposed that the atom must consist mainly of empty space with the mass concentrated in a tiny central core—the nucleus.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/11 The Structure of Atoms: Protons and Neutrons The mass of the atom is primarily in the nucleus
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/12 The Structure of Atoms: Protons and Neutrons The charge of the proton is opposite in sign but equal to that of the electron
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/13 Atomic Number Atomic Number (Z): Number of protons in an atom’s nucleus. Equivalent to the number of electrons around the atom’s nucleus. Mass Number (A): The sum of the number of protons and the number of neutrons in an atom’s nucleus. Isotope: Atoms with identical atomic numbers but different mass numbers.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/14 Atomic Number carbon-14 C 14 6 atomic number mass number carbon-12 C 12 6 atomic number mass number 6 protons 6 electrons 8 neutrons 6 protons 6 electrons 6 neutrons
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/15 Atomic Mass The mass of 1 atom of carbon-12 is defined to be 12 amu. Atomic Mass: The weighted average of the isotopic masses of the element’s naturally occurring isotopes.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/16 Atomic Mass carbon-12:98.89 % natural abundance12 amu carbon-13:1.11 % natural abundance amu Why is the atomic mass of the element carbon amu? = amu mass of carbon = (12 amu)(0.9889) + ( amu)(0.0111) = amu amu
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/17 Compounds and Mixtures Same compositionVariable composition
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/18 Compounds and Mixtures Variable properties Similar properties
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/19 Compounds and Mixtures Cannot be separated physically The same number of protons
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/20 Molecules, Ions, and Chemical Bonds Covalent Bond: Results when two atoms share several (usually two) electrons. Typically a nonmetal bonded to a nonmetal.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/21 Molecules, Ions, and Chemical Bonds Ionic Bond: A transfer of one or more electrons from one atom to another. An electrostatic attraction between charged particles.Typically a metal bonded to a nonmetal. Ion: A charged particle. Cation: A positively charged particle. Metals tend to form cations. Anion: A negatively charged particle. Nonmetals tend to form anions.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/22 Molecules, Ions, and Chemical Bonds Na 1+ + Cl 1- Na + Cl 11 protons 10 electrons 17 protons 18 electrons 11 protons 11 electrons 17 protons 17 electrons In the formation of sodium chloride, one electron is transferred from the sodium atom to the chlorine atom.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/23 Molecules, Ions, and Chemical Bonds
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/24 Acids and Bases Acid: A substance that provides H 1+ ions in water. HCl, HNO 3, H 2 SO 4, H 3 PO 4 Turns litmus red. Base: A substance that provides OH 1- ions in water. NaOH, KOH, Ba(OH) 2 Turns litmus blue.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/25 Acids and Bases Sulfuric acid: H 1+ (aq) + SO 4 2- (aq)HSO 4 1- (aq) H2OH2O Hydrochloric acid: H 1+ (aq) + Cl 1- (aq)HCl(g) H2OH2O Nitric acid: H 1+ (aq) + NO 3 1- (aq)HNO 3 (l) H2OH2O H 1+ (aq) + HSO 4 1- (aq)H 2 SO 4 (l) H2OH2O
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/26 Acids and Bases Sodium hydroxide: Na 1+ (aq) + OH 1- (aq)NaOH(s) H2OH2O Barium hydroxide: Ba 2+ (aq) + 2OH 1- (aq)Ba(OH) 2 (s) H2OH2O
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/ Naming Chemical Compounds Cation Charges for Typical Main-Group Ions
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/28 1- Naming Chemical Compounds Anion Charges for Typical Main-Group Ions 3-2-
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/29 Naming Chemical Compounds Some transition metals form more than one cation
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/30 Naming Chemical Compounds Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges. aluminum sulfide:Al 2 S 3 Al 3+ S 2- sodium chloride:NaClNa 1+ Cl 1- magnesium oxide:MgOMg 2+ O 2- Binary Ionic Compounds
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/31 Naming Chemical Compounds Stock System: Use Roman numerals in parentheses to indicate the charge on metals that form more than one kind of cation. lead(II) fluoride:PbF 2 Pb 2+ F 1- iron(III) oxide:Fe 2 O 3 Fe 3+ O 2- tin(II) chloride:SnCl 2 Sn 2+ Cl 1- Binary Ionic Compounds
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/32 Naming Chemical Compounds Molecular Compound (Molecule): The unit of matter that results when two or more atoms are joined by covalent bonds. Because nonmetals often combine with one another in different proportions to form different compounds, numerical prefixes are usually included in the names of binary molecular compounds.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/33 Naming Chemical Compounds N2F4N2F4 The second element listed is more anionlike and takes the name of the element with an “ide” modification to the ending. The first element listed is more cationlike and takes the name of the element. The prefix is added to the front of each to indicate the number of each atom. dinitrogen tetrafluoride
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/34 Naming Chemical Compounds Binary Molecular Compounds dinitrogen tetroxideN2O4N2O4 carbon monoxideCO Whenever the prefix for the first element is “mono,” drop it. Whenever the prefix ends in “a” or “o” and the element name begins with a vowel, drop the “a” or “o” in the prefix. carbon dioxideCO 2
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/35 Naming Chemical Compounds
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/36 Naming Chemical Compounds Polyatomic Ionic Compounds sodium carbonate:Na 2 CO 3 Na 1+ CO 3 2- iron(II) hydroxide:Fe(OH) 2 Fe 2+ OH 1- magnesium carbonate:MgCO 3 Mg 2+ CO 3 2- sodium hydroxide:NaOHNa 1+ OH 1-
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/37 Naming Chemical Compounds Binary Acids HClhydrochloric acid HBrhydrobromic acid HFhydrofluoric acid
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 2/38 Naming Chemical Compounds “ate”“ic” “ite”“ous”