Atoms, Ions and Molecules The Building Blocks of Matter - Magnetic Resonance Imaging (MRI)
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1/22/2020 Atoms, Ions and Molecules The Building Blocks of Matter Chapter 2 1 Magnetic Resonance Imaging (MRI) The signal is produced by protons in the nucleus of the hydrogen atoms in H2O 2 1
1/22/2020 Chapter Outline 2.1 The Rutherford Model of Atomic Structure 2.2 Nuclides and Their Symbols 2.3 Navigating the Periodic Table 2.4 The Masses of Atoms, Ions, and Molecules 2.5 Moles and Molar Mass 2.6 Mass Spectrometry: Isotope Abundances and Molar Mass 3 Experiments in Atomic Structure • J. J. Thompson (1906 Nobel Prize in Physics) - cathode ray tube experiments; discovery of the electron; measurement of the charge-to-mass ratio. • Robert Millikan (1923 Nobel Prize in Physics) - oil-drop experiments; measured the mass of the electron, therefore calculate the charge • Ernest Rutherford (1908 Nobel Prize in Physics) - gold-foil experiments; the nuclear atom 4 2
1/22/2020 Marie Curie The Nobel Prize in Physics 1903 (shared) The Nobel Prize in Chemistry 1911 • Physics: discovery of spontaneous radioactivity • Chemistry: discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element 5 J.J. Thomson Cathode Ray Tube Experiments - Electrons 6 3
1/22/2020 Results of “Cathode Ray” Experiments • Travel in straight lines • invisible • independent of cathode composition • bend in a magnetic field like a negatively-charged particle would • charge/mass = -1.76 x 108 C/g 7 Thompson’s “Plum Pudding” Model of the Atom electrons distributed throughout a diffuse, positively charged sphere. 8 4
1/22/2020 Robert Millikan’s oil drop Experiment - measured the mass of the electron 9 Millikan’s Results • Fine mist of oil produced by an atomizer forms in the chamber • A positively charged repeller plate is below the mist • Under the influence of gravity, the drops pass through a small hole in the repeller plate • The oil drops were then ionized by a beam of X-rays, producing electrons which adhere to the oil drops • The voltage applied to the positive repeller plate was adjusted until droplets were suspended in mid-air • From the physics and knowledge of the size of the gravitational and electrostatic forces, the charge on each droplet could be calculated • The charge was measured to be -1.60 X 10-19 C • Using the mass to charge ratio measured by Thompson, the mass of the electron was calculated to be 9.11 X 10-28 g 10 5
1/22/2020 Radioactivity and the Nuclear Atom Spontaneous emission of particles and/or radiation from a decaying, unstable nucleus -particles = -particles = -rays = 11 12 6
1/22/2020 Ernest Rutherford - the nuclear atom 13 Rutherford's Observations b) Expected results from “plum c) Actual results. pudding” model. 1. the majority of particles penetrated undeflected 2. some particles were deflected at small angles 3. occasionally -particles scattered back at large angles 14 7
1/22/2020 Rutherford’s Conclusions • The atom is mainly empty space because most of the -particles passed through undeflected • The nucleus is very dense and positively charged because some of the -particles were repulsed and deflected • Electrons occupy the space around the nucleus • The atom is electrically neutral 15 Rutherford’s Model of the Atom atomic radius ~ 100 pm = 1 x 10-10 m nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m If the nucleus was the size of an orange, then the radius of the atom would be 2.5 miles 16 8
1/22/2020 mass p mass n = 1840 x mass e- 17 Chapter Outline 2.1 The Rutherford Model of Atomic Structure 2.2 Nuclides and Their Symbols 2.3 Navigating the Periodic Table 2.4 The Masses of Atoms, Ions, and Molecules 2.5 Moles and Molar Mass 2.6 Making Elements 2.7 Artificial Nuclides 18 9
1/22/2020 Atomic Mass Units • Atomic Mass Units (amu) • Comprise a relative scale to express the masses of atoms and subatomic particles. • Scale is based on the mass of 1 atom of carbon: » 6 protons + 6 neutrons = 12 amu. • 1 amu = 1 Dalton (Da) 19 Isotopes: Experimental Evidence 20 10
1/22/2020 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes (nuclides) are atoms of the same element with different numbers of neutrons in the nucleus Mass Number A ZX Element Symbol Atomic Number 1 2 3 1H 1H (D) 1H (T) 235 238 92 U 92 U 21 Practice: Isotopic Symbols • Several nuclides of gaseous elements are useful for the MRI of pulmonary function. Write symbols in the form A ZX for the nuclides that have 36 protons and 47 neutrons. • Collect and Organize: • Analyze: • Solve: • Think about It: 22 11
1/22/2020 Practice: Identifying Atoms and Ions • Complete the missing information in the table. 23 Chapter Outline 2.1 The Rutherford Model of Atomic Structure 2.2 Nuclides and Their Symbols 2.3 Navigating the Periodic Table 2.4 The Masses of Atoms, Ions, and Molecules 2.5 Moles and Molar Mass 2.6 Making Elements 2.7 Artificial Nuclides 24 12
1/22/2020 The Periodic Table of the Elements Mendeleev’s Periodic Table Dmitrii Mendeleev (1872): • Ordered elements by atomic mass. • Arranged elements in columns based on similar chemical and physical properties. • Left open spaces in the table for elements not yet discovered. 25 The Modern Periodic Table • Also based on a classification of elements in terms of their physical and chemical properties. • Horizontal rows: called periods (1 → 7). • Columns: contain elements of the same family or group (1 →18). • Several groups have names as well as numbers. 26 13
1/22/2020 27 Metals, Metalloids, and Nonmetals metals metalloids nonmetals 28 14
1/22/2020 Navigating the Modern Periodic Table – Groups and Families 29 Groups of Elements (cont.) 30 15
1/22/2020 31 Common Charges of Cations and Anions • Cation has lost electrons and is positively charged • Anion has gained electrons and is negatively charged • Note the relationship between charge and group # 32 16
1/22/2020
These 7 elements occur naturally as diatomics (memorize)
H2 N2 F2 O2 I2 Cl2 Br2
33
Metals
• found to the left of the “diagonal
line”
• lose electrons in chemical
reactions
• solids (except for Hg, Cs, and Fr)
• conduct electricity
• ductile (draw into a wire)
• malleable (roll into sheets)
• form alloys ("solid-solution" of
one metal in another)
34
171/22/2020 Nonmetals • found to the right of the “diagonal line” • like to gain electrons from metals, or share electrons among themselves • found as solids, liquids (Br), and gases (Inert gases, and H, N, O, F, Cl) • “diatomics” - H2, N2, F2, O2 ,I2, Cl2, Br2 • oxygen also exist as ozone, O3 • insulators (except for graphite or C) Helium-Neon lasers 35 Metalloids • elements next to the “diagonal line” • B, Si, Ge, As, Sb, and Te • physical properties of a metal (can be “convinced” to conduct electricity) and chemical properties of a nonmetal Elemental Si is used in the semiconductor industry 36 18
1/22/2020 Chapter Outline 2.1 The Rutherford Model of Atomic Structure 2.2 Nuclides and Their Symbols 2.3 Navigating the Periodic Table 2.4 The Masses of Atoms, Ions, and Molecules 2.5 Moles and Molar Mass 2.6 Making Elements 2.7 Artificial Nuclides 37 Average Atomic Mass Weighted average mass of natural sample of an element, calculated by multiplying the natural abundance (%abn) of each isotope by its exact mass in amu’s and then summing up these products. NOTE: you must divide the %abn by 100 first AM = (mass 1)(abn) + (mass 2)(abn) + (mass 3)(abn) + etc. Divided by 100 0.904838 0.002696 0.092465 38 19
1/22/2020 Average Atomic Mass of Ne Calculation 39 Average Atomic Masses Any sample of an element always contains the same percentage of each type of isotope, e.g. if you have 100 grams of Ne, then using the %abn’s given previously, you have - 90.4838 g of Neon-20 0.2696 g of Neon-21 9.2465 g of Neon 22 The most abundant isotope has an atomic mass closest to the average atomic mass given in the Periodic Table, e.g. Most abundant isotope of Ne is Neon-20 because its average atomic mass from the Periodic Table = 20.180 amu 40 20
1/22/2020 Molecular Mass (Molecular Weight) Molecular Mass = the sum of the average atomic masses of the atoms in the molecule. e.g. H2SO4 41 Formula Units and Formula Mass Formula Units – for ionic compounds, the smallest electrically neutral unit in an ionic compound Formula Mass – the sum of the average atomic masses of the cations and anions that make up a neutral formula unit e.g. NaCl 42 21
1/22/2020 Chapter Outline 2.1 The Rutherford Model of Atomic Structure 2.2 Nuclides and Their Symbols 2.3 Navigating the Periodic Table 2.4 The Masses of Atoms, Ions, and Molecules 2.5 Moles and Molar Mass 2.6 Making Elements 2.7 Artificial Nuclides 43 The Mole - The mole is the Chemist’s counting unit pair dozen gross =2 = 12 = 144 Avogadro’s Number ream = (NA) = 6.022 X 1023 500 = 1 mole of atoms, molecules, ions, etc. 44 22
1/22/2020 One Mole of: He Cu, Fe, S, and Hg 1 foot 45 Experiment – 12C • Remember that 12C is our reference and has a mass of exactly 12 amu (exact number). • Count the number of atoms of 12C that add up to exactly 12 grams • This number is called Avogadro’s Number NA = 6.022 x 1023 • So there are 12 g of 12C per mole, or we write: AW = 12 g/mol 46 23
1/22/2020 Therefore, if Avogadro’s Number of 12C adds up to 12.0 grams, then what would Avogadro’s Number of, for example, 24Mg atoms weigh, if each atom is 23.99 amu? The Magnesium atoms (baseballs) are heavier than Carbon- 12 atoms (golf balls), and have a mass ratio of 23.99/12. Adding up the same number of C and Mg atoms has the same ratio. Therefore a mole of Mg weighs 23.99 grams! 47 Significance of the Mole Mass in Equivalent to Mass in amu’s grams/mole NA of Hg atoms weigh __________ NA of Si atoms weigh __________ 48 24
1/22/2020 Moles, Mass, and Particles How to convert between number of particles number of moles (and vica-versa) 49 Sample Exercise 2.6 The silicon used to make computer chips has to be extremely pure. Fpr example, it must contain less than 3 x 10-10 moles of phosphorus (a common impurity in Si) per mole of silicon. What is this level of impurity expressed in atoms of phosphorus per mole of Si? 50 25
1/22/2020 Converting Between Moles, Numbers of Particles, and Mass Using the Molar Mass (M) and NA as Conversion Factors e.g. carbon 12.011 grams 1 mole mole 12.011 grams e.g. H2SO4 sulfuric acid 98.0 grams 1 mole mole 98.0 grams 51 Converting Between Moles, Numbers of Particles, and Mass Using the Molar Mass (M) and NA as Conversion Factors 1 = Mass Divide by M moles of Multiply by NA Numbers Multiply by M particles Divide by NA of particles = 1 This procedure works for both elements and molecules 52 26
1/22/2020 Example Involving Elements (a) How many moles of K atoms are present in 19.5 g of potassium? (b) How many atoms of K are there? 53 Example Involving Molecules How many moles are present in 58.4 g of chalk (CaCO3)? 54 27
1/22/2020 Example Involving Molecules Convert 2.45 x 1018 molecules of KCl to grams 55 Calculations Involving an Element of Groups of Elements Within a Molecule You must use the chemical formula to form a ratio: • How many atoms of N are there in a molecule of Fe(NO3)2? • How many oxygen atoms are there? • How many nitrate ions (NO3-) are there? 56 28
1/22/2020 The Uranium used in nuclear fuel exists in nature in several minerals, e.g. carnotite 1. Calculate how many moles of Uranium are found in 100.0 grams of carnotite, K2(UO2)2(VO4)2•3H2O. MW = 902.2 g/mol 2. How many grams of Uranium are there? 57 Summary 58 29
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