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Chapter 4 Chemical Foundations: Elements, Atoms, and Ions Chapter 4 Table of Contents 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 The Elements Symbols for the Elements Dalton’s Atomic Theory Formulas of Compounds The Structure of the Atom Introduction to the Modern Concept of Atomic Structure Isotopes Introduction to the Periodic Table 4.9 4.10 4.11 Natural States of the Elements (see Part 2) Ions (see Part 2) Compounds That Contain Ions (see Part 2) Copyright © Cengage Learning. All rights reserved 2 Section 4.1 The Elements • • • 114 known (officially named) 88 found in nature, 26 are man made. Just as you had to learn the 26 letters of the alphabet before you learned to read and write, you need to learn the names and symbols of the chemical elements before you can read and write chemistry. Return to TOC Copyright © Cengage Learning. All rights reserved 3 Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 4 Section 4.1 The Elements How the Term Element is Used • • • Could mean a single atom of that element (Ar or H). Could mean molecules of an element (H2), which is hydrogen found in its natural state (diatomic). Could mean atoms of elements are present in some form (sodium found in the human body). Return to TOC Copyright © Cengage Learning. All rights reserved 5 Section 4.1 The Elements • • Most elements are very reactive. Elements are not generally found in uncombined form. Exceptions are: • Noble metals – gold, platinum and silver • Noble gases – Group 8 Return to TOC Copyright © Cengage Learning. All rights reserved 6 Section 4.1 The Elements Diatomic Molecules • Nitrogen gas contains N2 molecules. Copyright © Cengage Learning. All rights reserved • Oxygen gas contains O2 molecules. Return to TOC 7 Section 4.1 The Elements Diatomic Molecules Return to TOC Copyright © Cengage Learning. All rights reserved 8 Section 4.1 The Elements • Atoms can form ions by gaining or losing electrons. Metals tend to lose one or more electrons to form positive ions called cations. Cations are generally named by using the name of the parent atom. Return to TOC Copyright © Cengage Learning. All rights reserved 9 Section 4.1 The Elements • Nonmetals tend to gain one or more electrons to form negative ions called anions. • Anions are named by using the root of the atom name followed by the suffix –ide. Return to TOC Copyright © Cengage Learning. All rights reserved 10 Section 4.1 The Elements Ion Charges and the Periodic Table • The ion that a particular atom will form can be predicted from the periodic table. Group or Family Alkali Metals (1A) Alkaline Earth Metals (2A) Halogens (7A) Noble Gases (8A) Charge 1+ 2+ 1– 0 Return to TOC Copyright © Cengage Learning. All rights reserved 11 Section 4.1 The Elements Ion Charges and the Periodic Table Return to TOC Copyright © Cengage Learning. All rights reserved 12 Section 4.1 The Elements • • Ions combine to form ionic compounds. Properties of ionic compounds High melting points Conduct electricity • • If melted If dissolved in water Return to TOC Copyright © Cengage Learning. All rights reserved 13 Section 4.1 The Elements • • Ionic compounds are electrically neutral. The charges on the anions and cations in the compound must sum to zero. Return to TOC Copyright © Cengage Learning. All rights reserved 14 Section 4.1 The Elements Formulas for Ionic Compounds • • Write the cation element symbol followed by the anion element symbol. The number of cations and anions must be correct for their charges to sum to zero. Return to TOC Copyright © Cengage Learning. All rights reserved 15 Section 4.2 Symbols for the Elements • • • Each element has a unique one- or two-letter symbol. First letter is always capitalized and the second is not. The symbol usually consists of the first one or two letters of the element’s name. • Examples: Oxygen Krypton O Kr Sometimes the symbol is taken from the element’s original Latin or Greek name. Examples: Gold Au Lead Pb aurum plumbum Return to TOC Copyright © Cengage Learning. All rights reserved 16 Section 4.2 Symbols for the Elements Names and Symbols of the Most Common Elements Return to TOC Copyright © Cengage Learning. All rights reserved 17 Section 4.4 Formulas of Compounds Chemical Formulas Describe Compounds • • Compound – distinct substance that is composed of the atoms of two or more elements and always contains exactly the same relative masses of those elements. Chemical Formulas – expresses the types of atoms and the number of each type in each unit (molecule) of a given compound. Return to TOC Copyright © Cengage Learning. All rights reserved 18 Section 4.4 Formulas of Compounds Rules for Writing Formulas 1. Each atom present is represented by its element symbol. 2. The number of each type of atom is indicated by a subscript written to the right of the element symbol. 3. When only one atom of a given type is present, the subscript 1 is not written. Return to TOC Copyright © Cengage Learning. All rights reserved 19 Section 4.4 Formulas of Compounds Exercise The pesticide known as DDT paralyzes insects by binding to their nerve cells, leading to uncontrolled firing of the nerves. Before most uses of DDT were banned in the U.S., many insects had developed a resistance to it. Write out the formula for DDT. It contains 14 carbon atoms, 9 hydrogen atoms, and 5 atoms of chlorine. C14H9Cl5 Return to TOC Copyright © Cengage Learning. All rights reserved 20 Section 4.6 Introduction to the Modern Concept of Atomic Structure The atom contains: • • • Electrons – found outside the nucleus; negatively charged Protons – found in the nucleus; positive charge equal in magnitude to the electron’s negative charge Neutrons – found in the nucleus; no charge; virtually same mass as a proton Return to TOC Copyright © Cengage Learning. All rights reserved 21 Section 4.6 Introduction to the Modern Concept of Atomic Structure • The nucleus is: Small compared with the overall size of the atom. Extremely dense; accounts for almost all of the atom’s mass. Return to TOC Copyright © Cengage Learning. All rights reserved 22 Section 4.6 Introduction to the Modern Concept of Atomic Structure Return to TOC Copyright © Cengage Learning. All rights reserved 23 Section 4.6 Introduction to the Modern Concept of Atomic Structure Why do different atoms have different chemical properties? • • • The chemistry of an atom arises from its electrons. Electrons are the parts of atoms that “intermingle” when atoms combine to form molecules. It is the number of electrons that really determines chemical behavior. Return to TOC Copyright © Cengage Learning. All rights reserved 24 Section 4.6 Introduction to the Modern Concept of Atomic Structure • 1 EARTH = 6.775235700E9 PEOPLE • 1 PURE COPPER • 1 PENNY = 2.4E22 ATOMS MOLE OF ANY SUBSTANCE = 6.022E23 ATOMS Return to TOC Copyright © Cengage Learning. All rights reserved 25 Section 4.7 Isotopes Isotopes • • • Atoms with the same number of protons but different numbers of neutrons. Show almost identical chemical properties; chemistry of atom is due to its electrons. In nature most elements contain mixtures of isotopes. Return to TOC Copyright © Cengage Learning. All rights reserved 26 Section 4.7 Isotopes Two Isotopes of Sodium Return to TOC Copyright © Cengage Learning. All rights reserved 27 Section 4.7 Isotopes Isotopes A Z • • • X X = the symbol of the element Z = the atomic number (# of protons) A = the mass number (# of protons and neutrons) Return to TOC Copyright © Cengage Learning. All rights reserved 28 Section 4.7 Isotopes Isotopes – An Example 14 6 • • • C C = the symbol for carbon 6 = the atomic number (6 protons) 14 = the mass number (6 protons and 8 neutrons) 12 6 C • C = the symbol for carbon • 6 = the atomic number (6 protons) • 12 = the mass number (6 protons and 6 neutrons) Return to TOC Copyright © Cengage Learning. All rights reserved 29 Section 4.7 Isotopes Exercise A certain isotope X contains 23 protons and 28 neutrons. • What is the mass number of this isotope? • Identify the element. Mass Number = 51 Vanadium Return to TOC Copyright © Cengage Learning. All rights reserved 30 Section 4.8 Introduction to the Periodic Table The Periodic Table • The periodic table shows all of the known elements in order of increasing atomic number. Return to TOC Copyright © Cengage Learning. All rights reserved 31 Section 4.8 Introduction to the Periodic Table The Periodic Table • • • Metals vs. Nonmetals Groups or Families – elements in the same vertical columns; have similar chemical properties Periods – horizontal rows of elements Return to TOC Copyright © Cengage Learning. All rights reserved 32 Section 4.8 Introduction to the Periodic Table The Periodic Table • • • Most elements are metals and occur on the left side. The nonmetals appear on the right side. Metalloids are elements that have some metallic and some nonmetallic properties. Return to TOC Copyright © Cengage Learning. All rights reserved 33 Section 4.8 Introduction to the Periodic Table • ATOMIC NUMBER - the number of protons in the nucleus of an atom • # OF ELECTRONS (NEGATIVELY CHARGED) EQUALS THE # OF PROTONS (POSITIVELY CHARGED) • MASS NUMBER – total number of protons and neutrons in the nucleus • # OF NEUTRONS = MASS # - ATOMIC # Return to TOC Copyright © Cengage Learning. All rights reserved 34 Section 4.8 Introduction to the Periodic Table NAME SYMBOL ATOMIC # PROTONS NEUTRONS MASS # ELECTRONS OSMIUM 24 36 Er Return to TOC Copyright © Cengage Learning. All rights reserved 35 Section 4.8 Introduction to the Periodic Table Physical Properties of Metals 1. Efficient conduction of heat and electricity 2. Malleability (they can be hammered into thin sheets) 3. Ductility (they can be pulled into wires) 4. A lustrous (shiny) appearance Return to TOC Copyright © Cengage Learning. All rights reserved 36