Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 4 Lecture History of the Atomic Model Basic Chemistry Fifth Edition Chapter 4 Atoms and Elements 4.3 The Atom • Democritus (400 B.C.) • Believed that matter was composed of invisible particles of matter he called atoms. • Antoine Lavoisier (1700’s) • Law of Conservation of Mass – Matter is not created or destroyed. • Joseph Proust (1700’s) Learning Goal Describe the electrical charge and location in an atom for a proton, a neutron, and an electron. History of the Atomic Model • John Dalton (Late 1700’s) • First atomic theory explaining chemical reactions • Law of constant composition – compounds are composed of atoms in definite ratios. History of the Atomic Model • Henri Bacquerel (1896) • While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very penetrating rays. • J.J. Thomson (1897) • Discovered the electron using cathode ray tubes. • Proposed the Electron Cloud model, or more commonly called the “Plum Pudding” model Thomsen’s “Plum Pudding” Model of the Atom J.J.Thomsen • discovered that cathode rays were streams of small negatively charged particles called electrons • proposed the “plum pudding” model of an atom in which protons and electrons were distributed throughout the atom 5 Basic Chemistry History of the Atomic Model • Marie Curie (1898) • Studied uranium and thorium and called their spontaneous decay process "radioactivity,” leading Rutherford to discover the alpha particle. • Hantaro Nagaok (1903) • Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. • Robert Millikan (1909) • Found the charge and mass of the electron in his famous “oil-can” experiment. Copyright © 2011 Pearson Education, Inc. 1 Milikan Oil Drop Experiment (1909) History of the Atomic Model • Ernest Rutherford (1911) • Discovered the nucleus in his famous “gold foil” experiment. • Using voltage and change in the rate of fall of charged oil drops, he was able to determine the charge on each drop. • From Thompson’s charge to mass ratio, Milikan determined the charge and mass of an electron. Particles of Radioactivity • Three types of radiation were discovered by Ernest Rutherford: particles particles rays Rutherford’s Gold Foil Experiment (1911) Since some particles were deflected at large angles, Thompson’s model could not be correct. • Data from his experiments led Rutherford to propose a planetary model in which a cloud of electrons surrounded a small, compact nucleus of positive charge. Only such a concentration of charge could produce the electric field strong enough to cause the heavy deflection of alpha particles observed. Rutherford’s Gold Foil Experiment (1911) Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. James Chadwick (1932) Further developed the atomic model by theorizing that alpha and beta radiation results from the decomposition of a neutral particle found in the nucleus, the neutron • H atoms - 1 p; He atoms - 2 p • mass He/mass H should = 2 • measured mass He/mass H = 4 2 Subatomic Particles Atoms contains subatomic particles: • protons have a positive (+) charge • electrons have a negative (-) charge • like charges repel and unlike charges attract • neutrons are neutral Structure of the Atom An atom consists • of a nucleus that contains protons and neutrons • of electrons in the large empty space around the nucleus In an atom, the protons and neutrons are in the nucleus, whereas the electrons are contained in the large space outside the nucleus. Like charges repel, and unlike charges attract. 13 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Atomic Mass Scale • • • • 14 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Particles in the Atom On the atomic mass scale for subatomic particles, 1 atomic mass unit (amu) is equal to 1/12 of the mass of the carbon-12 atom a proton has a mass of 1.007 amu a neutron has a mass of about 1.008 amu an electron has a very small mass of 0.00055 amu 15 Basic Chemistry Copyright © 2011 Pearson Education, Inc. 16 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Chapter 4 Lecture Learning Check Basic Chemistry Fifth Edition Is each of the following statements true or false? A. The mass of an electron is greater than the mass of a proton. B. Protons have a positive charge, and electrons have a negative charge. C. The nucleus of an atom contains only the protons and neutrons. Chapter 4 Atoms and Elements 4.4 Atomic Number and Mass Number Learning Goal Given the atomic number and the mass number of an atom, state the number of protons, neutrons, and electrons. 3 Atomic Number Atomic Numbers and Protons The atomic number • is specific for each element • is the same for all atoms of an element • is equal to the number of protons in an atom • appears above the symbol of an element 11 Na Atomic Number Symbol 19 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Learning Check B. A sulfur atom 1) 32 protons 2) 16 protons 3) 6 protons C. A barium atom 1) 137 protons 2) 81 protons 3) 56 protons Basic Chemistry • Hydrogen has atomic number 1, every H atom has one proton. • Carbon has atomic number 6, every C atom has six protons. • Copper has atomic number 29, every Cu atom has 29 protons. • Gold has atomic number 79, every Au atom has 79 protons. 20 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Electrons in an Atom State the number of protons in each atom. A. A nitrogen atom 1) 5 protons 2) 7 protons 3) 14 protons 21 Examples: Copyright © 2011 Pearson Education, Inc. An atom of any element • is electrically neutral; the net charge of an atom is zero • the number of protons is equal to the number of electrons Example: An atom of aluminum Group 3A (13) has 13 protons and 13 electrons. It has a net charge of zero. 13 protons (13 +) + 13 electrons (13 -) = 0 22 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Mass Number Learning Check The mass number • represents the number of particles in the nucleus • is equal to the Number of protons + Number of neutrons An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 2) 35 3) 65 B. How many neutrons are in the zinc atom? 1) 30 2) 35 3) 65 C. What is the mass number of a zinc atom that has 37 neutrons? 1) 37 2) 65 3) 67 23 Basic Chemistry Copyright © 2011 Pearson Education, Inc. 24 Basic Chemistry Copyright © 2011 Pearson Education, Inc. 4 Chapter 4 Lecture Learning Check Basic Chemistry Fifth Edition An atom has 14 protons and 20 neutrons. Chapter 4 A. Its atomic number is 1) 14 2) 16 3) 34 Atoms and Elements 4.5 Isotopes and Atomic Mass B. Its mass number is 1) 14 2) 16 3) 34 2) Ca 3) Se C. The element is 1) Si 25 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Learning Goal Determine the number of protons, neutrons, and electrons in one or more of the isotopes of an element; calculate the atomic mass of an element using the percent abundance and mass of its naturally occurring isotopes. Isotopes Nuclear Symbol Isotopes A nuclear symbol • are atoms of the same element that have different mass numbers • represents a particular atom of an element • have the same number of protons, but different numbers of neutrons 27 Basic Chemistry Copyright © 2011 Pearson Education, Inc. • gives the mass number in the upper left corner and the atomic number in the lower left corner Example: An atom of magnesium with an atomic number of 12 and a mass number of 24 has the following atomic symbol: 28 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Information from Nuclear Symbols Learning Check • The nuclear symbol indicates the number of protons (p+), neutrons, (n), and electrons (e -) in a particular atom. Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following. 16 31 8 15 O 8 p+ 8n 8 e- 29 Basic Chemistry P 15 p+ 16 n 15 e- 65 30 Zn 30 p+ 35 n 30 e- Copyright © 2011 Pearson Education, Inc. 12C 6 13C 6 6 protons ______ neutrons ______ ______ ______ electrons ______ ______ ______ 30 Basic Chemistry ______ 14C ______ Copyright © 2011 Pearson Education, Inc. 5 Learning Check Learning Check Write the nuclear symbols for atoms with the following subatomic particles: A. 8 p+, 8 n, 8 e- ___________ B. 17 p+, 20 n, 17e- ___________ 1. Which of the following pairs are isotopes of the same element? 2. In which of the following pairs do both atoms have 8 neutrons? A. 15X 8 C. 47 p+, 60 n, 47 e- ___________ Basic Chemistry 12X C. 15X 16X 7 8 32 Copyright © 2011 Pearson Education, Inc. 7 B. 6 31 15X Basic Chemistry 14X 6 Copyright © 2011 Pearson Education, Inc. Isotopes of Magnesium Atomic Mass The atomic mass of an element • is listed below the symbol of each element on the periodic table 11 Na 22.99 In naturally occurring magnesium, there are three isotopes. • gives the mass of an “average” atom of each element compared to 12C • is not the same as the mass number 33 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Examples of Isotopes and Their Atomic Masses 34 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Calculating Atomic Mass The calculation for atomic mass requires the Most elements have two or more isotopes that contribute to the atomic mass of that element. • percent(%) abundance of each isotope • atomic mass of each isotope of that element • sum of the weighted averages mass isotope(1) x (%) + mass isotope(2) x (%) + … 100 100 35 Basic Chemistry Copyright © 2011 Pearson Education, Inc. 36 Basic Chemistry Copyright © 2011 Pearson Education, Inc. 6 Atomic Mass of Magnesium Calculating Atomic Mass Isotope Mass The atomic mass of Mg • is due to all the Mg isotopes • is a weighted average • is not a whole number Abundance 24Mg = 23.99 amu x 78.70/100 25Mg = 24.99 amu x 10.13/100 = 2.531 amu 26Mg = 25.98 amu x 11.17/100 = 2.902 amu = 18.88 amu Atomic mass (average mass) Mg = 24.31 amu Mg 24.31 37 Basic Chemistry 38 Copyright © 2011 Pearson Education, Inc. Learning Check __________ B. aluminum __________ C. lead __________ D. barium __________ E. iron __________ Copyright © 2011 Pearson Education, Inc. Atomic Mass for Cl Using the periodic table, specify the atomic mass of each element: A. calcium Basic Chemistry • The atomic mass of chlorine is the weighted average of two isotopes 35Cl and 37Cl. Chlorine, with two naturally occurring isotopes, has an atomic mass of 35.45. 39 Basic Chemistry 40 Copyright © 2011 Pearson Education, Inc. Calculating Atomic Mass for Cl 35Cl has atomic mass 34.97 (75.76%) and 37C atomic mass 36.97 (24.24%). • Use the atomic mass and percent of each isotope to calculate the contribution of each isotope to the weighted average. 34.97 x 75.76 = 26.49 amu 100 35.97 x 24.24 = 8.962 amu 100 35.45 amu has Basic Chemistry Copyright © 2011 Pearson Education, Inc. Learning Check Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.11% of 69Ga (atomic mass 68.93) atoms and 39.89% of 71Ga (atomic mass 70.92) atoms. What is the atomic mass of gallium? • The sum is the weighted average or atomic mass of Cl. 35.45 amu 41 Basic Chemistry Copyright © 2011 Pearson Education, Inc. 42 Basic Chemistry Copyright © 2011 Pearson Education, Inc. 7