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Chapter 4 Chemical Foundations: Elements, Atoms, and Ions Copyright © Cengage Learning. All rights reserved 1 Section 4.1 The Elements • • • 118 known: 88 found in nature, others are made in laboratories. Abundance is the percentage found in nature. Oxygen most abundant element (by mass) on earth and in the human body. Copyright © Cengage Learning. All rights reserved 2 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 aurum Lead Pb plumbum Copyright © Cengage Learning. All rights reserved 3 Section 4.3 Dalton’s Atomic Theory Dalton’s Atomic Theory (1808) 1. Elements are made of tiny particles called atoms. - tiny, hard, unbreakable, spheres 2. All atoms of a given element are identical. - all carbon atoms have the same chemical and physical properties. 3. Atoms of a given element are different from those of any other element. - carbon atoms have different chemical and physical properties than sulfur atoms. Copyright © Cengage Learning. All rights reserved 4 Section 4.3 Dalton’s Atomic Theory Law of Constant Composition 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. • A given compound always has the same composition, regardless of where it comes from. 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. Copyright © Cengage Learning. All rights reserved 5 Section 4.3 Dalton’s Atomic Theory Dalton’s Atomic Theory (continued) 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. Copyright © Cengage Learning. All rights reserved 6 Section 4.3 Dalton’s Atomic Theory Dalton’s Atomic Theory (continued) 5. Atoms are indivisible in a chemical process. - all atoms present at beginning are present at the end. - atoms are not created or destroyed, just rearranged - atoms of one element cannot change into atoms of another element (Lead cannot be turned into Gold by a chemical reaction) Copyright © Cengage Learning. All rights reserved 7 Section 4.3 Dalton’s Atomic Theory 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. Copyright © Cengage Learning. All rights reserved 8 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. Copyright © Cengage Learning. All rights reserved 9 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. Copyright © Cengage Learning. All rights reserved 10 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 Copyright © Cengage Learning. All rights reserved 11 Section 4.5 The Structure of the Atom J. J. Thomson (1898—1903) • • • • • Investigated a beam called a cathode ray He determined that the ray was made of tiny negatively charge particles we call electrons. His measurements led him to conclude that these electrons were smaller than a hydrogen atom. If electrons are smaller than atoms, they must be pieces of the atom. The atom must be breakable. He found that atoms of different elements all produce these electrons. Copyright © Cengage Learning. All rights reserved 12 Section 4.5 The Structure of the Atom The ELECTRON - Tiny, negatively charge particle - Very light compared to the mass of the atom. ( 1/1836th the mass of a Hydrogen atom. - Move very rapidly within the atom Copyright © Cengage Learning. All rights reserved 13 Section 4.5 The Structure of the Atom 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. Copyright © Cengage Learning. All rights reserved 14 Section 4.5 The Structure of the Atom Thomson’s Plum Pudding Model • The atom IS breakable!! • The atom has structure. • Electrons suspended in a positively charge electric field. – must have positive charge to balance negative charge of electrons and make the atom neutral. • Mass of the atom is due to electrons. • Atom is mostly “empty” space. - compared size of the electrons to size of the atom Copyright © Cengage Learning. All rights reserved 15 Chapter 4 Table of Contents Rutherford’s Gold Foil Experment • How can you prove something is empty? • put something through it – use large target atoms • use very thin sheets of target so do not absorb “bullet” – use very small particle as bullet with very high energy • but not so small that electrons will affect it • bullet = alpha particles, target atoms = gold foil – particles have a mass of 4 amu & charge of +2 c.u. – gold has a mass of 197 amu & is very malleable Copyright © Cengage Learning. All rights reserved 16 Chapter 4 Table of Contents Rutherford’s experiment on α-particle bombardment of metal foil. Copyright © Cengage Learning. All rights reserved 17 Chapter 4 Table of Contents Rutherford’s Results • Over 98% of the particles went straight through • About 2% of the particles went through but were deflected by large angles • About 0.01% of the particles bounced off the gold foil Copyright © Cengage Learning. All rights reserved 18 Chapter 4 Table of Contents (a) The results that the metal foil experiment would have yielded if the plum pudding model had been correct. (b) Actual results. Copyright © Cengage Learning. All rights reserved 19 Section 4.5 The Structure of the Atom Ernest Rutherford (1911) • • • • Explained the nuclear atom. Atom has a dense center of positive charge called the nucleus. Electrons travel around the nucleus in the empty space at a relatively large distance. A proton has the same magnitude of charge as the electron, but its charge is positive. Copyright © Cengage Learning. All rights reserved 20 Section 4.5 The Structure of the Atom Rutherford and Chadwick (1932) • • Most nuclei also contain a neutral particle called the neutron. A neutron is slightly more massive than a proton but has no charge. Copyright © Cengage Learning. All rights reserved 21 Section 4.5 The Structure of the Atom Structure of the Nucleus • The nucleus was found to be composed of two kinds of particles • Some of these particles are called protons – charge = +1 – mass is about the same as a hydrogen atom • Since protons and electrons have the same amount of charge, for the atom to be neutral there must be equal numbers of protons and electrons • The other particle is called a neutron – has no charge – has a mass slightly more than a proton Copyright © Cengage Learning. All rights reserved 22 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 Copyright © Cengage Learning. All rights reserved 23 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. Copyright © Cengage Learning. All rights reserved 24 Section 4.6 Introduction to the Modern Concept of Atomic Structure Copyright © Cengage Learning. All rights reserved 25 Section 4.6 Introduction to the Modern Concept of Atomic Structure A nuclear atom viewed in cross section. Copyright © Cengage Learning. All rights reserved 26 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. Copyright © Cengage Learning. All rights reserved 27 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. Copyright © Cengage Learning. All rights reserved 28 Section 4.7 Isotopes Two Isotopes of Sodium Copyright © Cengage Learning. All rights reserved 29 Section 4.7 Isotopes Isotopes A Z • • • X X = the symbol of the element A = the mass number (# of protons and neutrons) Z = the atomic number (# of protons) Copyright © Cengage Learning. All rights reserved 30 Section 4.7 Isotopes Isotopes – An Example 14 6 • • • • • • 12 6 C Name of element carbon Number of protons (6 protons) Number of neutrons (8 neutrons) Copyright © Cengage Learning. All rights reserved • • • • • • C Name of element carbon Number of protons (6 protons) Number of neutrons (6 neutrons) 31 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. • Copyright © Cengage Learning. All rights reserved Mass Number = 51 Vanadium 32 Section 4.7 Isotopes Elements • Arranged in a pattern called the Periodic Table • Position on the table allows us to predict properties of the element • Metals – about 75% of all the elements – lustrous, malleable, ductile, conduct heat and electricity • Nonmetals – dull, brittle, insulators • Metalloids – also know as semi-metals – some properties of both metals & nonmetals Copyright © Cengage Learning. All rights reserved 33 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. Copyright © Cengage Learning. All rights reserved 34 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 Copyright © Cengage Learning. All rights reserved 35 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. Copyright © Cengage Learning. All rights reserved 36 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 Copyright © Cengage Learning. All rights reserved 37 Section 4.8 Introduction to the Periodic Table Physical Properties of Nonmetals 1. Lack properties of metals 2. Exhibit much variation in properties 3. Can be gases, liquids, or solids Copyright © Cengage Learning. All rights reserved 38 Section 4.8 Introduction to the Periodic Table Physical Properties of Metalloids 1. Exhibit a mixture of metallic and non-metallic properties Copyright © Cengage Learning. All rights reserved 39 Section 4.8 Introduction to the Periodic Table • • 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 Copyright © Cengage Learning. All rights reserved 40 Section 4.8 Introduction to the Periodic Table Diatomic Molecules • Nitrogen gas contains N2 molecules. Copyright © Cengage Learning. All rights reserved • Oxygen gas contains O2 molecules. 41 Section 4.8 Introduction to the Periodic Table Diatomic Molecules Copyright © Cengage Learning. All rights reserved 42 Section 4.8 Introduction to the Periodic Table Important Group - Halogens • Group 7A = Halogens • very reactive nonmetals • react with metals to form ionic compounds • HX all acids • Fluorine = F2 – pale yellow gas • Chlorine = Cl2 – pale green gas • Bromine = Br2 – brown liquid that has lots of brown vapor over it – Only other liquid element at room conditions is the metal Hg • Iodine = I2 – lustrous, purple solid Copyright © Cengage Learning. All rights reserved 43 Section 4.8 Introduction to the Periodic Table Allotropes • Many solid nonmetallic elements can exist in different forms with different physical properties, these are called allotopes. • Different forms of a given element. • Example: Solid carbon occurs in three forms. • Diamond • Graphite • Buckminsterfullerene Copyright © Cengage Learning. All rights reserved 44 Section 4.8 Introduction to the Periodic Table Carbon Allotropes Copyright © Cengage Learning. All rights reserved 45 Section 4.8 Introduction to the Periodic Table • 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. Copyright © Cengage Learning. All rights reserved 46 Section 4.8 Introduction to the Periodic Table • 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. Copyright © Cengage Learning. All rights reserved 47 Section 4.8 Introduction to the Periodic Table 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) Copyright © Cengage Learning. All rights reserved Charge 1+ 2+ 1– 0 48 Section 4.8 Introduction to the Periodic Table Ion Charges and the Periodic Table Copyright © Cengage Learning. All rights reserved 49 Section 4.8 Introduction to the Periodic Table Electrical Nature of Matter • Some substances dissolve in water to form a solution that conducts well - these are called electrolytes • When dissolved in water, electrolyte compounds break up into component ions – ions are atoms or groups of atoms that have an electrical charge Copyright © Cengage Learning. All rights reserved 50 Section 4.8 Introduction to the Periodic Table Exercise An ion with a 3+ charge contains 23 electrons. Which ion is it? a) b) c) d) Fe3+ V3+ Ca3+ Sc3+ Copyright © Cengage Learning. All rights reserved 51 Section 4.8 Introduction to the Periodic Table Exercise A certain ion X+ contains 54 electrons and 78 neutrons. What is the mass number of this ion? • Copyright © Cengage Learning. All rights reserved 133 52