Chemical Foundations: Elements, Atoms, and Ions Chapter 4

Section 4.1 The Elements Return to TOC 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 4.10Ions 4.11Compounds That Contain Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved known: 88 found in nature, others 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. It’s just like learning a foreign language. You have to learn the vocabulary and grammar before you can read and write sentences!

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). Could mean atoms of elements that are present in some form (sodium found in the human body). Look at each particular case to determine its proper use. How the Term Element is Used

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 6 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 7 Names and Symbols of the Most Common Elements

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 8 1.Most natural materials are mixtures of pure substances. 2.Pure substances are either elements or combinations of elements called compounds. 3.A given compound always contains the same proportions (by mass) of the elements.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 9 A given compound always has the same composition, regardless of where it comes from.  There is always one oxygen for each two hydrogens in a molecule of water [O mol.wt = 16; H mol.wt. = 1 X 2 H’s per water]  Water always contains 8 g of oxygen for every 1 g of hydrogen.  Carbon dioxide always contains 2.7 g of oxygen for every 1 g of carbon. Law of Constant Composition

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 10 1.Elements are made of tiny particles called atoms. Dalton’s Atomic Theory (1808) 2.All atoms of a given element are identical. 3.The atoms of a given element are different from those of any other element. 4.Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 11 5.Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together. Dalton’s Atomic Theory (continued)

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 12 Scanning Tunneling Microscope

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 13 Concept Check Which of the following statements regarding Dalton’s atomic theory are still believed to be true? I. Elements are made of tiny particles called atoms. II. All atoms of a given element are identical. III. A given compound always has the same relative numbers and types of atoms. IV. Atoms are indestructible.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 14 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 15 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 16 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 17 Postulated the existence of electrons using cathode-ray tubes. The atom must also contain positive particles that balance exactly the negative charge carried by particles that we now call electrons. J. J. Thomson (1898—1903)

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 18 Cathode-Ray Tube + e-e- -

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 19 William Thomson (Plum Pudding Model) Reasoned that the atom might be thought of as a uniform “pudding” of positive charge with enough negative electrons scattered within to counterbalance that positive charge

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 20 Explained the nuclear atom. Atom has a dense center of positive charge called the nucleus. Electrons travel around the nucleus at a relatively large distance. A proton has the same magnitude of charge as the electron, but its charge is positive. Ernest Rutherford (1911) Nobel Prize 1908

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 21 Most nuclei also contain a neutral particle called the neutron. A neutron is slightly more massive than a proton but has no charge. Rutherford and Chadwick (1932)

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 22 Rutherford’s Experiment

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 23 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 24 The nucleus is:  Small compared with the overall size of the atom.  Extremely dense; accounts for almost all of the atom’s mass.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 25

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 26 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 27 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 28 Two Isotopes of Sodium

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 29 Isotope Notation How many protons, neutrons and electrons in each of the following: protons neutrons electrons 23 Na 14 N 38 Ar 35 Cl 36 Cl Fe Protons Neutrons Electrons

Section 4.1 The Elements 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 31 Mendeleev’s Table Mendeleev arranged the elements in order of increasing relative atomic mass (protons had not been discovered yet). The elements on the modern periodic table are arranged in order of increasing atomic number. He also grouped elements with similar properties into columns and rows so that the properties of the elements varied in a regular pattern (periodically). 2 - Mendeleev’s Table Russian chemist Dmitri Mendeleev developed and published the basic arrangement of the periodic table between 1869 and 1871.

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 32 Mendeleev’s Table 2 -

Section 4.1 The Elements 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 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 34 Groups or Families – elements in the same vertical columns; have similar chemical properties Periods – horizontal rows of elements The Periodic Table

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 35 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 Magnesium Platinum Sliver Gold Copper

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 36 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 4.9 Natural States and Elements Helium Neon Argon Krypton Xenon

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 37 Diatomic Molecules Nitrogen gas contains N 2 molecules. Oxygen gas contains O 2 molecules. Section 4.9 Natural States and Elements

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 38 Diatomic Molecules Section 4.9 Natural States and Elements

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 39 Nonmetals Liquid Nitrogen Selenium Phorphorus Bromine Chlorine Fluorine Sulfur Graphite

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 40 Different forms of a given element. Example:  Solid carbon occurs in three forms. Diamond Graphite Buckminsterfullerene Carbon Allotropes Section 4.9 Natural States and Elements

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 41 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 4.10 Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 42 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 4.10 Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 43 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 4.10 Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 44 Conductivity of Solutions Containing Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 45 Ion Charges and the Periodic Table Section 4.10 Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 46 Exercise An ion with a 3+ charge contains 23 electrons. Which ion is it? a)Fe 3+ b)V 3+ c)Ca 3+ d)Sc 3+ Section 4.10 Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 47 Exercise A certain ion X + contains 54 electrons and 78 neutrons. What is the mass number of this ion? 133 Section 4.10 Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 48 Ions combine to form ionic compounds. Properties of ionic compounds  High melting points  Conduct electricity If melted If dissolved in water Section 4.11 Compounds that Contain Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 49 Ionic compounds are electrically neutral. The charges on the anions and cations in the compound must sum to zero. Section 4.11 Compounds that Contain Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 50 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 4.11 Compounds that Contain Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 51 Concept Check A compound contains an unknown ion X and has the formula XCl 2. Ion X contains 20 electrons. What is the identity of X? a)Ti 2+ b)Sc + c)Ca 2+ d)Cr 2+ Section 4.11 Compounds that Contain Ions

Section 4.1 The Elements Return to TOC Copyright © Cengage Learning. All rights reserved 52 Concept Check A member of the alkaline earth metal family whose most stable ion contains 36 electrons forms a compound with bromine. What is the correct formula for this compound? a)CaBr 2 b)KrBr c)RbBr d)SrBr 2 Section 4.11 Compounds that Contain Ions