Chemistry Atomic Theories Part 2 PDF

The Discovery of the Nucleus J. J. Thomson proposed that the negatively charged electrons were small particles held within a...

The Discovery of the Nucleus J. J. Thomson proposed that the negatively charged electrons were small particles held within a positively charged sphere. Aka chocolate-chip model Copyright © 2023 Pearson Canada Inc. 2-1  Rutherford’s Gold Foil Experiment alpha particles: 2 protons+2 neutrons, have positive charge bombarded gold foil with them most particles passed through in a straight line some (approximately 1 in 20 000) were deflected – why? Figure 2.6 Rutherford’s Gold Foil Experiment Copyright © 2023 Pearson Canada Inc. 2-2 Rutherford’s Nuclear Theory of the Atom mass and positive charge of an atom must be concentrated in a space much smaller than the size of the atom itself = nucleus Most of the atom's volume is empty space, throughout which tiny, negatively charged electrons are dispersed. Figure 2.7 The Nuclear Atom Copyright © 2023 Pearson Canada Inc. 2-3 Rutherford’s postulates The volume occupied by an atom must consist of a large amount of empty space. A small, relatively heavy, positively charged body, the nucleus, must be at the center of each atom. The nucleus contains most of the atom’s mass. Negatively charged electrons surround the nucleus. The proton, a positively charged, subatomic particle is located in the nucleus. Copyright © 2023 Pearson Canada Inc. 2-4 Sizes An atom has a diameter of about 1 × 10–8 cm and the nucleus has a diameter of about 1 × 10–13 cm. If an atom were the size of the Superdome, the nucleus would be the size of a marble. Superdome diameter = 680 feet (207.3 m), total floor area of 269,000 square feet (24,991 m2), interior space of 3,500,000 m3, capacity of 83 000 seats New Orleans, Louisiana, United States. It is the home stadium of the New Orleans Saints of the National Football League (NFL). Copyright © 2023 Pearson Canada Inc. 2-5  Protons, the Atomic Number, and Neutrons Based on the heaviness of the nucleus, Rutherford predicted that it must contain neutral particles in addition to protons. Neutrons, n0, were discovered by James Chadwick. A neutron is about the size of a proton without any charge. Copyright © 2023 Pearson Canada Inc. 2-6  Properties of Protons, Neutrons, and Electrons Table 2.1 Characteristics of Subatomic Particles Blank Mass (kg) Mass (u) Charge (relative) Charge (C) Proton 1.67262 × 10−27 1.00727 +1 +1.60218 × 10−19 Neutron 1.67493 × 10−27 1.00866 0 0 Electron 9.10938 × 10−31 5.48580 × 10−4 −1 −1.60218 × 10−19 Copyright © 2023 Pearson Canada Inc. 2-7  8 Atomic Notation Each element has a characteristic number of protons in the nucleus. This is the atomic number, Z. The total number of protons and neutrons in the nucleus of an atom is the mass number, A. We use atomic notation to display the number of protons and neutrons in the nucleus of an atom: Copyright © 2023 Pearson Canada Inc. 2-8 Isotopes: When the Number of Neutrons Varies Number of Number of A (Mass Natural Symbol Protons Neutrons Number) Abundance (%) Ne − 20 or 20 Ne 10 10 10 20 90.48 Ne − 21 or 21 Ne 10 10 11 21 0.27 Ne − 22 or 22 Ne 10 10 12 22 9.25 Copyright © 2023 Pearson Canada Inc. 2-9 Where to extract this information from? An example: Si The element is silicon (symbol Si). The atomic number is 14; silicon has 14 protons. The mass number is 29; the atom of silicon has 29 protons + neutrons. The number of neutrons is A – Z = 29 – 14 = 15 neutrons. Copyright © 2023 Pearson Canada Inc. 2 - 10 Copyright © 2023 Pearson Canada Inc. 2 - 11  Examples 1. 2. 3. 4. Copyright © 2023 Pearson Canada Inc. 2 - 12 Exercise Copyright © 2023 Pearson Canada Inc. 2 - 13 Ions: Losing or Gaining Electrons Li → Li+ + 1e− cations are positively charged ions F + 1e− → F− anions are negatively charged ions In a neutral molecule, the charge or sum of charges of the cation must be equal to the charge or sum of charges of the anion. Copyright © 2023 Pearson Canada Inc. 2 - 14 Isotopes All atoms of the same element have the same number of protons. Most elements occur naturally with varying numbers of neutrons. Isotopes are the atoms of the same element that have a different number of neutrons in the nucleus. Isotopes have the same atomic number, but different mass numbers. Copyright © 2023 Pearson Canada Inc. 2 - 15 Isotope Notation We often refer to an isotope by stating the name of the element followed by the mass number. Protium is 11𝐻 2 Deuterium is 1𝐻 How many protons and neutrons does an atom of lead-206 have? The atomic number of Pb is 82, so it has 82 protons. Pb-206 has 206 – 82 = 124 neutrons. Copyright © 2023 Pearson Canada Inc. 2 - 16 2.5 Atomic Mass: The Average Mass of an Element’s Atoms Atomic mass =  (χ n )  (mn ) n Atomic mass = χ 1m1 + χ 2 m2 + χ 3 m3 + K + χ n mn χn is the fraction of isotope n mn is the mass of isotope n Copyright © 2023 Pearson Canada Inc. 2 - 17 Calculating Atomic Mass Chlorine has two naturally occurring isotopes 35Cl has m35 = 34.968853 amu and abundance χ35 = 75.77% 37Cl has m37 = 36.965903 amu and abundance χ37 = 24.23% Atomic mass = (χ n )  (mn ) Weighted average mass = χ 35 m35 + χ 37 m37 = (34.968853 amu )(0.7577) + (36.965903 amu )(0.2423) = 35.45 amu Copyright © 2023 Pearson Canada Inc. 2 - 18 Example Copyright © 2023 Pearson Canada Inc. 2 - 19 Mass Spectrometry: Measuring the Mass of Atoms and Molecules 1. Ionization: The atom is ionized by knocking one or more electrons off to give a positive ion. This is true even for things which you would normally expect to form negative ions (chlorine, for example) or never form ions at all (argon, for example). Mass spectrometers always work with positive ions. 2: Acceleration: The ions are accelerated so that they all have the same kinetic energy. 3: Deflection: The ions are then deflected by a magnetic field according to their masses. The lighter they are, the more they are deflected. The amount of deflection also depends on the number of positive charges on the ion - in other words, on how many electrons were knocked off in the first stage. The more the ion is charged, the more it gets deflected. 4: Detection: The beam of ions passing through the machine is detected electrically. Jim Clark (Chemguide.co.uk) Copyright © 2023 Pearson Canada Inc. 2 - 20 Figure 2.8 A Time-of-Flight Mass Spectrometer kinetic energy =1/2 mv2 (where m is the mass of the ion and v is the velocity) ions with different masses have different velocities. ions enter a field-free region where they drift based on their velocities the time it takes each packet of ions to reach the detector is measured. The lightest ions have a higher velocity and reach the detector first, and the heaviest ions have a lower velocity and reach the detector later. Copyright © 2022 Pearson Canada Inc. 2 - 21 Mass Spectrum Figure 2.9 Mass Spectrum of Xenon Copyright © 2023 Pearson Canada Inc. 2 - 22 2.7 The Periodic Table of the Elements Dmitri Mendeleev’s periodic table from 1871. Mendeleev organized the known elements into eight groups, in order of increasing mass. [Dmitri Mendeleev] Copyright © 2023 Pearson Canada Inc. 2 - 23 Modern Periodic Table (1 of 2) Figure 2.10 Metals, Nonmetals, and Metalloids [Sr, Matthias Zepper; Cr, Charles D. Winters/Science Source; Au, Steffen Foerster/Shutterstock; Cu, Clive Streeter/DK Images; Pb, Tom Bochsler/Pearson Education; Si, Enricoros; As, Harry Taylor/DK Images; C, Gary Ombler/DK Images; S, Mirek Hejnicki/Fotolia; Br, Charles D. Winters/Science Source] Copyright © 2023 Pearson Canada Inc. 2 - 24 Modern Periodic Table (2 of 2) Figure 2.11 The Periodic Table Main-Group and Transition Elements Copyright © 2023 Pearson Canada Inc. 2 - 25 Group 1 Elements [© Richard Megna/Fundamental Photographs, NYC] [Martyn F. Chillmaid/Science Source] Copyright © 2023 Pearson Canada Inc. 2 - 26 Group 17 Elements [Charles D. Winters/Science Source] [Charles D. Winters/Science Source] Copyright © 2023 Pearson Canada Inc. 2 - 27 Ions and the Periodic Table Figure 2.12 Main-Group Elements That Form Ions with Predictable Charges Copyright © 2023 Pearson Canada Inc. 2 - 28