Chapter 1 Chemical Foundations
Chapter 1 Table of Contents (1.1) (1.2) (1.3) (1.4) (1.5) (1.6) (1.7) Chemistry: An atoms-first approach The scientific method The early history of chemistry Fundamental chemical laws Dalton s atomic theory Early experiments to characterize the atom The modern view of atomic structure: An introduction
Chapter 1 Questions to Consider How do chemicals in a battery cause the production of electricity? Why is lead harmful for human consumption? How do hormones influence human behavior? How does nail polish remover work?
Section 1.1 Chemistry: An Atoms-First Approach Importance of Studying About Atoms It provides a better understanding about: Macroscopic structures and their behavior Formation of different molecules Attraction between molecules Study of chemistry is based on a proper understanding of atoms Forms the basis of solutions to many problems
Section 1.1 Chemistry: An Atoms-First Approach Figure 1.1 - Atoms Seen through an STM Microscope
Section 1.1 Chemistry: An Atoms-First Approach Understanding Atoms The macroscopic world comprises objects such as cars, glass, rocks, oceans, etc Made of atoms Understanding the structure and behavior of different atoms helps in a better purview of the macroscopic world
Section 1.1 Chemistry: An Atoms-First Approach Figure 1.2 - Grains of Sand on a Beach
Section 1.1 Chemistry: An Atoms-First Approach Understanding Atoms There are only about 100 different types of atoms They combine in various proportions to form all known substances Properties of a substance are determined by the arrangement of its atoms
Section 1.1 Chemistry: An Atoms-First Approach Atoms vs. Molecules Matter is composed of tiny particles called atoms Atom - The smallest part of an element that is still that element Molecule - Two or more atoms joined and acting as a unit
Section 1.1 Chemistry: An Atoms-First Approach Diatomic Molecules Chemical elements that naturally possess two atoms
Section 1.1 Chemistry: An Atoms-First Approach
Section 1.1 Chemistry: An Atoms-First Approach A Chemical Reaction One substance changes to another by reorganizing the way the atoms are attached to each other
Section 1.2 The Scientific Method Fundamental Steps of the Scientific Method A sequence that scientists use in the study of nature Helps solve problems effectively Mastery of the scientific approach makes for excellent problem solvers
Section 1.2 The Scientific Method Science A framework for gaining and organizing knowledge A set of facts with a plan of action A procedure for processing and understanding certain types of information Scientific method: The basis on which a scientific enquiry is conducted It varies according to the nature of the problem encountered
Section 1.2 The Scientific Method Scientific Models Theory (model): Set of tested hypotheses that gives an overall explanation of some natural phenomenon Observation A witnessed phenomenon that can be recorded Interpretation A possible explanation of the reason behind the phenomenon
Section 1.2 The Scientific Method Scientific Methods Natural law: An observation that applies to many different systems Law of conservation of mass: The total mass of materials is not affected by a chemical change in those materials A law is a statement on how a particular phenomenon occurs A theory is an attempt to explain why a phenomenon occurs
Section 1.3 The Early History of Chemistry Early History of Chemistry Greeks were the first to attempt to provide a reason behind chemical equations They believed that all matter was composed of earth, air, fire, and water Alchemy was prevalent for the next 2000 years Several elements were discovered Methods to prepare mineral acids were developed Robert Boyle was the first chemist Quantified the relationship between pressure and air Copyright Cengage Learning. All rights reserved 17
Section 1.3 The Early History of Chemistry Robert Boyle and Other Pioneers of Chemistry Introduced quantitative physics and chemistry Declared that elements cannot be further broken down Phased out the Greek system of describing elements All views were not accurate Metals were not true elements Georg Stahl Suggested the existence of phlogiston Joseph Priestly discovered the existence of oxygen
Section 1.4 Fundamental Chemical Laws Three Important Laws Law of conservation of mass Mass is neither created nor destroyed Stated by Antoine Lavosier Law of definite proportion E.g., CH 4 + 2O 2 CO 2 + 2H 2 0 A given compound always contains exactly the same proportion of elements by mass Stated by Joseph Proust
Section 1.4 Fundamental Chemical Laws Three Important Laws Law of multiple proportions When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers Stated by John Dalton
Section 1.4 Fundamental Chemical Laws Example 1.1 - Illustrating the Law of Multiple Proportions The following data were collected for several compounds of nitrogen and oxygen Show how these data illustrate the law of multiple proportions
Section 1.4 Fundamental Chemical Laws Solution For the law of multiple proportions to hold, the ratios of the masses of nitrogen combining with 1 gram of oxygen in each pair of compounds should be small whole numbers. Therefore, the ratios can be computed as follows A 1.750 2 = = B 0.8750 1 B 0.8750 2 = = C 0.4375 1 A 1.750 4 = = C 0.4375 1
Section 1.5 Dalton s Atomic Theory Dalton s Atomic Theory (1808) Each element is made up of tiny particles called atoms The atoms of a given element are identical The atoms of different elements are different in some fundamental way or ways Chemical compounds are formed when atoms of different elements combine with each other A given compound always has the same relative numbers and types of atoms Copyright Cengage Learning. All rights reserved 23
Section 1.5 Dalton s Atomic Theory Dalton s Atomic Theory Chemical reactions involve reorganization of the atoms changes in the way they are bound together Atoms themselves are not changed in a chemical reaction
Section 1.5 Dalton s Atomic Theory Dalton s Atomic Theory Dalton prepared the first table of atomic masses Also called atomic weights Most of his masses were not accurate Incorrect assumptions about the formulas of certain compounds
Section 1.5 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. III. All atoms of a given element are identical A given compound always has the same relative numbers and types of atoms IV. Atoms are indestructible
Section 1.5 Dalton s Atomic Theory Joseph Gay-Lussac and Avogadro (1809 1811) Joseph Gay-Lussac Measured the volumes of gases that reacted with each other Identical conditions of temperature and pressure were used Avogadro s hypothesis At the same temperature and pressure, equal volumes of different gases contain the same number of particles Applies if the distance between gas particles is very great
Section 1.5 Dalton s Atomic Theory Figure 1.8 - Combining Gas Volumes
Section 1.5 Dalton s Atomic Theory Figure 1.9 - Combining Gases at the Molecular Level
Section 1.6 Early Experiments to Characterize the Atom J. J. Thomson Conducted experiments using cathode-ray tubes High voltage applied to partially evacuated tubes Assumed that the cathode ray comprised of electrons Determined the charge-to-mass ratio of an electron e 8 = 1.76 10 C/g m e is the charge of the electron in coulombs m is the mass in grams
Section 1.6 Early Experiments to Characterize the Atom Figure 1.11 - The Cathode-Ray Tube
Section 1.6 Early Experiments to Characterize the Atom The Plum Pudding Model Hypothesized by Thomson Atoms are made of a positively charged cloud Negative electrons are embedded at random
Section 1.6 Early Experiments to Characterize the Atom Determining the Charge of an Electron Robert Millikan Performed experiments involving charged oil drops Determined the magnitude of the charge on a single electron Calculated the mass of the electron 9.11 10 31 kg
Section 1.6 Early Experiments to Characterize the Atom Figure 1.14 (a) - Determining the Charge of an Electron
Section 1.6 Early Experiments to Characterize the Atom Radioactivity Accidentally discovered by Henri Becquerel A uranium-containing mineral produced its image on a photographic plate in the dark Types of radioactive emission Gamma rays (γ) - High-energy light Beta particles (β) - High-speed electrons Alpha particles (α) - Possess a charge twice that of the electron, with the opposite sign
Section 1.6 Early Experiments to Characterize the Atom The Nuclear Atom Discovered by Ernest Rutherford in 1911 Alpha particles were made to pass through foil and hit a detector Some particles were deflected and never hit the detector Deflection of α particles was attributed to a highly concentrated center of positive charge, which was termed the nucleus
Section 1.6 Early Experiments to Characterize the Atom Figure 1.17 (a) and (b) - Expected and Actual Results of the Metal Foil Experiment
Section 1.7 The Modern View of Atomic Structure Composition of an Atom Protons: Found in the nucleus Positive charge equal in magnitude to the electron s negative charge Electrons: Found outside the nucleus Negatively charged Neutrons: Found in the nucleus No charge Virtually the same mass as a proton
Section 1.7 The Modern View of Atomic Structure Composition of an Atom The nucleus is: Small compared to the overall size of the atom Extremely dense Accounts for almost all of the atom s mass A pea-sized nucleus would have a mass of 250 million tons
Section 1.7 The Modern View of Atomic Structure All Atoms have the Same Components but Different Chemical Properties Caused by differences in: The number of electrons The arrangement of electrons Electrons of different atoms intermingle to form molecules The degree of interaction in an atom is determined by the number of electrons it possesses
Section 1.7 The Modern View of Atomic Structure Isotopes Atoms with the same number of protons but different numbers of neutrons 23 Na 11 11 is the atomic number (Z) Number of protons 23 is the mass number (A) Total number of protons and neutrons
Section 1.7 The Modern View of Atomic Structure Figure 1.19 - Two Isotopes of Sodium
Section 1.7 The Modern View of Atomic Structure Interactive Example 1.2 - Writing the Symbols for Atoms Write the symbol for the atom that has an atomic number of 9 and a mass number of 19 How many electrons and how many neutrons does this atom have?
Section 1.7 The Modern View of Atomic Structure Solution The atomic number 9 means the atom has 9 protons. This element is called fluorine, symbolized by F. The atom is represented as: 19 9 F It is called fluorine nineteen. Since the atom has 9 protons, it also must have 9 electrons to achieve electrical neutrality. The mass number gives the total number of protons and neutrons, which means that this atom has 10 neutrons
Section 1.7 The Modern View of Atomic Structure Ions Atoms are electrically neutral Atoms can be assigned a net charge by either removing or adding an electron Charged atoms are called ions
Section 1.7 The Modern View of Atomic Structure Assigning a Charge to an Atom Atoms are turned into positive ions when they are stripped of an electron They are called cations Consider removing an electron from sodium Na Na + e +
Section 1.7 The Modern View of Atomic Structure Assigning a Charge to Atoms Atoms are turned into negative ions when an electron is added They are called anions Consider adding an electron to chlorine Cl + e Cl