Chemical Foundations: Elements, Atoms, and Ions Chapter 4

Table of Contents Copyright © Cengage Learning. All rights reserved The Elements 4.2 Symbols for the Elements 4.3 Dalton’s Atomic Theory 4.4 Formulas of Compounds 4.5 The Structure of the Atom 4.6Introduction to the Modern Concept of Atomic Structure 4.7Isotopes 4.8Introduction to the Periodic Table 4.9Natural States of the Elements (see Part 2) 4.10Ions (see Part 2) 4.11Compounds That Contain Ions (see Part 2)

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 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.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 4

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 5 Could mean a single atom of that element (Ar or H). Could mean molecules of an element (H 2 ), 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). How the Term Element is Used

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 6 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

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 7 Diatomic Molecules Nitrogen gas contains N 2 molecules. Oxygen gas contains O 2 molecules.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 8 Diatomic Molecules

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 9 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.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 10 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.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 11 Ion Charges and the Periodic Table The ion that a particular atom will form can be predicted from the periodic table. Group or FamilyCharge Alkali Metals (1A)1+ Alkaline Earth Metals (2A) 2+ Halogens (7A)1– Noble Gases (8A)0

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 12 Ion Charges and the Periodic Table

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 13 Ions combine to form ionic compounds. Properties of ionic compounds  High melting points  Conduct electricity If melted If dissolved in water

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 14 Ionic compounds are electrically neutral. The charges on the anions and cations in the compound must sum to zero.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 15 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. Formulas for Ionic Compounds

Section 4.2 Symbols for the Elements Return to TOC Copyright © Cengage Learning. All rights reserved 16 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 O Krypton Kr Sometimes the symbol is taken from the element’s original Latin or Greek name.  Examples: Gold Au aurum Lead Pb plumbum

Section 4.2 Symbols for the Elements Return to TOC Copyright © Cengage Learning. All rights reserved 17 Names and Symbols of the Most Common Elements

Section 4.4 Formulas of Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 18 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. Chemical Formulas Describe Compounds

Section 4.4 Formulas of Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 19 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. Rules for Writing Formulas

Section 4.4 Formulas of Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 20 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. C 14 H 9 Cl 5

Section 4.6 Introduction to the Modern Concept of Atomic Structure Return to TOC Copyright © Cengage Learning. All rights reserved 21 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

Section 4.6 Introduction to the Modern Concept of Atomic Structure Return to TOC Copyright © Cengage Learning. All rights reserved 22 The nucleus is:  Small compared with the overall size of the atom.  Extremely dense; accounts for almost all of the atom’s mass.

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 Return to TOC Copyright © Cengage Learning. All rights reserved 24 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. Why do different atoms have different chemical properties?

Section 4.6 Introduction to the Modern Concept of Atomic Structure Return to TOC 1 EARTH = E9 PEOPLE 1 PURE COPPER PENNY = 2.4E22 ATOMS 1 MOLE OF ANY SUBSTANCE = 6.022E23 ATOMS Copyright © Cengage Learning. All rights reserved 25

Section 4.7 Isotopes Return to TOC Copyright © Cengage Learning. All rights reserved 26 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. Isotopes

Section 4.7 Isotopes Return to TOC Copyright © Cengage Learning. All rights reserved 27 Two Isotopes of Sodium

Section 4.7 Isotopes Return to TOC Copyright © Cengage Learning. All rights reserved 28 X = the symbol of the element Z = the atomic number (# of protons) A = the mass number (# of protons and neutrons) Isotopes

Section 4.7 Isotopes Return to TOC Copyright © Cengage Learning. All rights reserved 29 Isotopes – An Example C = the symbol for carbon 6 = the atomic number (6 protons) 14 = the mass number (6 protons and 8 neutrons) C = the symbol for carbon 6 = the atomic number (6 protons) 12 = the mass number (6 protons and 6 neutrons)

Section 4.7 Isotopes Return to TOC Copyright © Cengage Learning. All rights reserved 30 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

Section 4.8 Introduction to the Periodic Table Return to TOC Copyright © Cengage Learning. All rights reserved 31 The periodic table shows all of the known elements in order of increasing atomic number. The Periodic Table

Section 4.8 Introduction to the Periodic Table Return to TOC Copyright © Cengage Learning. All rights reserved 32 Metals vs. Nonmetals Groups or Families – elements in the same vertical columns; have similar chemical properties Periods – horizontal rows of elements The Periodic Table

Section 4.8 Introduction to the Periodic Table Return to TOC Copyright © Cengage Learning. All rights reserved 33 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. The Periodic Table

Section 4.8 Introduction to the Periodic Table Return to TOC 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 # Copyright © Cengage Learning. All rights reserved 34

Section 4.8 Introduction to the Periodic Table Return to TOC NAMESYMBOL ATOMIC # PROTONSNEUTRONS MASS # ELECTRONS OSMIUM ErEr Copyright © Cengage Learning. All rights reserved 35

Section 4.8 Introduction to the Periodic Table Return to TOC Copyright © Cengage Learning. All rights reserved 36 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 Physical Properties of Metals