1 Atoms, Molecules, and IonsGeneral Chemistry I – Chapter 2

2 Objectives 1.0 Define key terms and concepts1.12 Demonstrate an understanding of the Law of Conservation of Matter, the Law of Multiple Proportions, and the Law of Definite Proportions. 1.13 Describe the structure of an atom using atomic theory. 1.14 Recognize and utilize trends on the periodic table. 1.15 Recognize the difference between covalent and ionic compounds. 1.16 Name chemical compounds and write their formulas.

3 Law of Conservation of MassThe mass of a reaction conducted in a closed system cannot be changed. While matter cannot be created or destroyed, it can be rearranged. HgO + heat  Hg + O2 The mass of the reactants must equal the mass of the products.

4 Law of Definite ProportionsA compound always contains the same elements in certain definite proportions and in no other combinations (H2O and H2O2) Also states that compounds have constant properties

5 The Law of Multiple ProportionsDifferent elements can be combined in multiple proportions to make different compounds. H2O and H2O2 NO, N2O, and NO2 CO and CO2

6 History of the Atom From Atomism to the Nuclear ModelJack F. Eichler Department of Chemistry University of California, Riverside

7 This case study will discuss…1. Where did the idea of atoms originate? What is the evidence that allows us to conclude that atoms exist? How have our models of the atom evolved over time? Let’s take a tour through a history of scientific discovery and find answers to these questions…

8 Democritus – Atomism (5th Century BCE)Readings in Ancient Philosophy: From Thales to Aristotle, edited by S Marc Cohen (2000).

9 What “evidence” did Democritus use to conclude that atoms exist?Since matter is not empty space, it must be made of uncuttable particles (atoms). If you divide up matter into smaller pieces for infinity, you end up with essentially nothing; since matter cannot be made up of nothing, it must have a small fundamental unit of matter that is uncuttable (atoms). The Greeks observed that chemical reactions could take place; reactions cannot take place unless matter is made up of uncuttable particles (atoms). Democritus did not use any evidence; he simply created the idea of atoms using his imagination. All of these are correct.

10 Democritus—Atomism

11 Dalton’s Atomic Theory (1805)Every element is made up of tiny particles called atoms. All atoms of a given element are identical to one another and different for atoms of other elements. Atoms of two or more different elements combine to form compounds. A particular compound is always made up of some kinds of atoms and the same number of each kind of atom. A chemical reaction involves the rearrangement, separation, or combination of atoms. Atoms are never created or destroyed during a chemical reaction.

12 Dalton’s Atomic Theory – Mass of Oxygen and Chromium in Two Samples of Chromium OxideSample #  Appearance  Mass of Cr (g)   Mass of O(g) orange crystals red powder red powder Sample #2 – if we have g of Cr, how many grams of O? g Cr/x g O = g Cr/ g O x = g O If sample #2 is CrO, what is the formula of sample #1? 0.9319/ = sample #1 must be CrO3 The content of this slide (and on slide 9) was adapted from “A Letter from Dalton” by Susan E. Groh, Problem-Based Learning Clearinghouse at University of Delaware, item#

13 What evidence did Dalton use to conclude that atoms exist?Since chromium oxide had two different types of compounds, it must be made up of chromium and oxygen atoms. Since the mass of chromium was the same in each sample, that indicates chromium must be made up of identical atoms. Since the two chromium oxide samples had different masses of oxygen, and the oxygen masses differed in whole number ratios, that suggests the compounds had different numbers of oxygen “units” (atoms); if the atoms could be “cut” up into different sizes, these whole number ratios would not exist. The different colors of the compounds indicated that each sample must be made up of different ratios of oxygen and chromium atoms. All of these are correct.

14 Dalton’s Atomic Theory – Mass of Oxygen and Chromium in Two Samples of Chromium OxideSample #  Appearance  Mass of Cr (g)   Mass of O(g) orange crystals red powder red powder Sample #2 – if we have g of Cr, how many grams of O? g Cr/x g O = g Cr/ g O x = g O If sample #2 is CrO, what is the formula of sample #1? 0.9319/ = sample #1 must be CrO3

15 Thomson Cathode Ray Tube (1897)

16 Thomson Cathode Ray Tube (1897)

17 Figure A Figure B Figure C Figure DWhich model of the atom is confirmed by the data/observations from the cathode ray tube experiment? Figure A Figure B Figure C Figure D

18 Rutherford Gold Foil Experiment (1911)

19 Figure A Figure B Figure C Figure DWhich model of the atom is confirmed by the data/observations from the gold foil experiment? Figure A Figure B Figure C Figure D

20 Rutherford Gold Foil Experiment (1911)vs.

21 Chadwick Beryllium Experiment (1932)Nuclear Model of the Atom: nucleus possesses protons and neutrons; “electron cloud” surrounds the nucleus.

22 Nuclear Model of the AtomElectron (-) Proton (+) Neutron

23 We know about the basic structure of atoms…how were atoms of the elements different from one another? How were they organized?

24 Relative Atomic Mass Example: H2OIn the late 1700’s and 1800’s, scientists such as Dalton were able to determine experimentally that when water formed, it took two “parts” of hydrogen by volume and one “part” of oxygen by volume. This suggested water was made of two hydrogen atoms and one oxygen atom. How does this relate to relative atomic mass?

25 Which of the following best explains how relative atomic mass could be determined from the type of data available to Dalton? By determining the mass of oxygen contained in a sample of water, its atomic mass could be determined. By comparing the masses of hydrogen and oxygen contained in a sample of water, the atomic masses could be determined. By comparing the mass of hydrogen in the two “parts” of hydrogen and the mass of oxygen in the one “part” of oxygen in water, the relative atomic masses could then be determined. A and B are correct. B and C are correct.

26 Relative Atomic Mass Example: H2OIf one part of oxygen weighs 8 times as much as two parts of hydrogen in a sample of water, then one oxygen atom weighs 8 times as much as 2 hydrogen atoms…this is relative atomic mass.

27 Mendeleev and the Periodic Table (1869)Mendeleev used atomic mass and periodic trends to order the elements; his table predicted the existence of elements not yet discovered at the time (Ga, Sc, Ge…). Periodic trends trumped atomic mass in some cases.

28 Mass Spectrometry: Identifying Masses of Atoms (J.J. Thompson – 1910)

29 Moseley’s Determination of Atomic Number (1913)Number of protons in nucleus corresponded to shift in energy of spectral lines (shift in wavelength) X-rays Excited e-’s Light emitted prism Spectral lines Sample of matter

30 How is it possible that the atomic number increases in order, yet the atomic masses do not?There is no relationship between the atomic number and mass of the atom. The masses of the protons for Te, I, and Xe have slightly different masses. Since the numbers of neutrons do not neccessarily increase from one atom to the next, it is possible for the atomic number to increase while the total mass does not increase. A and B are both correct. B and C are both correct.

31 Atomic Mass vs. Mass Number

32 Neutrons, Atomic Number, Mass Number, and Average Atomic MassH 1 H 2 1 H 3 1

33 The average atomic mass (amu) of hydrogen is listed as 1The average atomic mass (amu) of hydrogen is listed as 1.001amu on the periodic table. If the three isotopes of hydrogen have a mass of 1 amu, 2 amu, and 3 amu, respectively, how is this average atomic mass possible? Hydrogen-1, hydrogen-2 (deuterium), and hydrogen-3 (tritium) must have different numbers of neutrons, which then shifts the mass closer to amu. The natural abundance of hydrogen-1 must be higher than the natural abundance of the other two isotopes of hydrogen. The average atomic mass is a weighted average of the three isotopes, and since there is more hydrogen-1 in nature than either of the other two isotopes, the average is thus less than the simple average of the three isotope masses. A and B are both correct. B and C are both correct.

34 The Nuclear Model of the Atom Atomic Mass and Atomic Number+ - - + + - hydrogen-1 Atomic mass = 1 amu Atomic number =1 helium-4 Atomic mass = 4 amu Atomic number = 2

35 The next step…how do we get from the nuclear model of the atom to the current model of the atom?Quantum Theory!

36 Image Credits Unless otherwise noted below, images in this presentation were created by the author or by the National Center for Case Study Teaching in Science. Slide 1 Description: Stylized illustration of an atom. Source: © valdis torms - Fotolia.com, ID# Clearance: Licensed image. Slides 2 and 17 Description: Atom schema. Source: Halfdan, Wikimedia Commons, Clearance: Creative Commons Attribution-Share Alike 3.0 Unported license. Slide 4 Description: Carved Italian marble bust depicting Democritus at the Victoria and Albert Museum Knightsbridge London England. Source: Photo by Afshin Darian, Flickr, Clearance: Creative Commons Attribution 2.0 Generic license. Slide 6 Description: British physicist and chemist John Dalton ( ), painted by J. Lonsdale, engraved by C. Turner. Source: Image available from the United States Library of Congress's Prints and Photographs division under the digital ID cph.3b12511, Clearance: U.S. public domain because of expired copyright. Slide 10 Description: Photo of Crookes tube. Source: D-Kuru/Wikimedia Commons, Clearance: Creative Commons Attribution-Share Alike 3.0 Austria license. Slides 10 and 23 Description: Photo of J.J. Thomson. Source: GWS - The Great War: The Standard History of the All Europe Conflict (volume four) edited by H. W. Wilson and J. A. Hammerton (Amalgamated Press, London 1915), Clearance: U.S. public domain because of expired copyright. Slide 11 Description: Diagram of cathode ray tube. Source: Theresa Knott, Wikimedia Commons, Clearance: Creative Commons Attribution-Share Alike 3.0 Unported license. Slide 13 Description: Photo of Ernest Rutherford, circa 1910. Source: Wikimedia Commons,

37 Image Credits Slide 13: Description: Diagram of gold foil experiment.Source: John Hutchinson, Structure of an Atom, Clearance: Creative Commons Attribution 3.0 Unported license (CC BY 3.0). Slide 15 Description: Diagram of the nuclear deflection of alpha particles. Source: Wikimedia Commons, Clearance: This work has been released into the public domain by its author, Fastfission. Slide 16 Description: Photo of James Chadwick. Source: Clearance: U.S. public domain because of expired copyright. Slide 22 Description: Photo of Dmitri Mendeleev. Source: Wikimedia Commons, Clearance: U.S. public domain because of expired copyright. Slide 23 Description: Schema of typical mass spectrometer. Source: Devon Fyson, part of Clearance: U.S. public domain because it contains materials that originally came from the United States Geological Survey, an agency of the United States Department of Interior. Slide 24 Description: Photo of Henry Moseley. Source: Wikimedia Commons, Clearance: In the U.S. public domain because of expired copyright. Slide 27 Description: Illustration of deuterium and tritium Source: European Fusion Development Agreement (EFDA), Clearance: Used in accordance with EFDA’s terms of use, Slide 29 Description: Periodic table. Source: Wikimedia Commons, Clearance: Released to the public domain by author.

38 What Are Your Questions?

39 Cl Atomic Number and Mass 17 35.453 Chlorine Atomic NumberElement Symbol Element Name 35.453 Atomic Mass

40 Isotopes Atoms of the same element that have different number of neutrons. The number of protons is ALWAYS the same.

41 Isotopes

42 Radioactivity The spontaneous emission of radiation from certain unstable elements Rontgen and The Curies Half-Life the amount of time it takes for half of a radioactive substance to decay

43 Types of RadioactivityAlpha (α) The least energetic of the three types of radioactivity Made of up positively charged particles Identical to the nucleus of a helium atom Symbolized as He2+ Beta (β) The second most energetic form of radioactivity Made up of negatively charged particles (electrons) Symbolized as e- Gamma (γ) A form of electromagnetic radiation The most energetic and penetrating of all radiation Has medical applications

44 Calculating Atomic MassCalculate the Atomic Mass of Cl. 35Cl = amu with % abundance 37Cl = amu with % abundance

45 Atomic Number and Mass Name of Element Symbol Atomic NumberMass Number # of Protons # of Neutrons # of Electrons P 32 44  101 12 12   Silicon 15  82 125

46 What Are Your Questions?

47 Origins of the ElementsThe most abundant element in the universe is Hydrogen followed by Helium Hydrogen was produced by stars in the universe and the fusion of two Hydrogen atoms formed Helium. 73% of the universe is Hydrogen, 25% is Helium, and about 2% is comprised of the heavier elements. The heavier elements are created in older stars such as Red Giants and White Dwarfs due to the high pressure allowing for the fusion of He and C to make Oxygen and so on.

48 Elements and Symbols Chemical Symbol One- or two- letter abbreviation for a chemical element

49 Elemental Symbols to MemorizePlease learn the elemental names/symbols for the first 20 elements and Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, I, Kr, Xe, Ag, Sn, Au, Hg, and Pb

50 The Periodic Table

51 The Periodic Table

52 The Periodic Table: GroupsAlkali Metals Soft, shiny metals that are good conductors of electricity. React violently with water. Alkaline Earth Metals Shiny like alkali metals but not as reactive.

53 The Periodic Table: GroupsHalogens Strongly reactive and form compounds with most elements Noble Gases Unreactive and seldom found in combination with other elements Halogens Strongly reactive and form compounds with most elements Noble Gases Unreactive and seldom found in combination with other elements

54 Metals, Nonmetals, and MetalloidsShiny solids that are very malleable and ductile and good conductors of heat and electricity. Nonmetals Not very shiny, malleable or ductile and are poor conductors of heat and electricity Metalloids Semi-metals

55 Molecules and Ions Molecule Diatomic Molecule Diatomic ElementA combination of at least two atoms held in a definite arrangement by chemical forces, or bonds. Diatomic Molecule Contains two atoms Diatomic Element Molecule that contains two atoms of the same element H, N, O, F, Cl, Br, I Polyatomic Molecule A molecule containing more than two atoms

56 Molecules and Ions Ion Monoatomic Ions Polyatomic IonsAn atom or group of atoms that possesses a charge Cation Positively charged molecule Anion Negatively charged molecule Monoatomic Ions Contains only one atom, or ion Polyatomic Ions Contains many atoms, or ions

57 Variable Oxidation StatesOxidation Numbers Transition Metals Variable Oxidation States

58 Charge Balance and Writing FormulasChemical Formula (molecular formula) Indicates the elements and number of elements that make up a compound Write the element with the charge and then cross it over and down

59 Write the chemical formula formed when the following elements bond.Na and Cl Ca and Br H and O C and H N and I P and Li Al and F

60 Nomenclature Ionic Compounds Covalent Compounds (Molecular)Formed between metals and nonmetals Covalent Compounds (Molecular) Formed between two nonmetals

61 Determine whether the following compounds are covalent or ionic.Na and Cl Ca and Br H and O C and H N and I P and Li Al and F

62 Naming Ionic CompoundsThe name of the cation is the name of the element. Examples Na+ = sodium ion Mg2+ = magnesium ion The name of the anion is the root name of the element plus the suffix –ide. Cl- = chloride ion O2- = oxide ion

63 Naming Ionic CompoundsTo name the compounds of simple binary ionic compounds (those containing only two elements), simply name the ions. Examples NaCl = sodium chloride MgO = magnesium oxide

64 Name the following ionic compounds.Li2O NaBr AlBr3 BaO Na2S MgI2 CaCl2

65 Write the Formula for the Following Ionic CompoundsSodium Iodide Aluminum Chloride Lithium Bromide Hydrogen Fluoride Magnesium Sulfide Sodium Oxide Calcium Phosphide Cesium Nitride

66 Naming Ionic CompoundsTransition metals can have more than one positive ion form in an ionic bond Roman numerals are used the in naming of these compounds to identify the metal’s charge Examples CuCl2 = Copper (II) Chloride SnO2 = Tin (IV) Oxide

67 Naming Ionic CompoundsModern Name Latin Name Symbol Symbol with charge Traditional Name Stock System Name Copper Cuprum Cu Cu+1 Cuprous Copper (I) Cu+2 Cupric Copper (II) Iron Ferrum Fe Fe+2 Ferrous Iron (II) Fe+3 Ferric Iron (III) Mercury Hydrargyrum Hg Hg+1 Mercurous Mercury (I) Hg+2 Mercuric Mercury (II) Lead Plumbum Pb Pb+2 Plumbous Lead (II) Pb+4 Plumbic Lead (IV) Tin Stannum Sn Sn+2 Stannous Tin (II) Sn+4 Stannic Tin (IV)

68 Name/write the chemical formula for the following ionic compoundsCuCl FeBr3 MnO PbS2 Iron (II) Chloride Copper (II) Oxide Nickel (II) Phosphide Mercury (I) Chloride

69 Polyatomic Ions Polyatomic IonA group of atoms that has an electrical charge The charge is shared among the atoms that form the polyatomic ion -ate means more oxygens Phosphate, PO43- -ite means fewer oxygens Phosphite, PO33-

70 Naming Polyatomic IonsWriting Formulas Follows same rules as for ionic bonding Total charge of molecule always equals zero Naming Write positive metal first followed by name of polyatomic ion Examples H2SO4 Hydrogen Sulfate Ca2CO3 Calcium Carbonate

71 Name the following ionic compounds containing a polyatomic ion.Potassium Sulfate Sodium Carbonate Magnesium Hydroxide Copper (II) Nitrate Potassium Permanganate Manganese (II) Sulfite

72 Write the Formula for the Following Ionic Compounds.NaHCO3 NH4C2H3O2 Mg(NO3)2 K2CrO4 Ca(CN)2 Fe3(PO4)2

73 Naming Covalent CompoundsSimilar to ionic naming; however, a prefix is used to identify the number of each element present in the name Examples CH4 = carbon tetrahydride NO2 = nitrogen dioxide

74 Name the following covalent compounds.CS2 PCl3 P2O5 N2O4 Cl2O SiF4 IBr3 SO2

75 Write the formula for the following covalent compounds.Phosphorus tribromide Iodine Pentafluoride Silicon tetrachloride Dinitrogen oxide Tetraphosphorus hexoxide Dinitrogen pentoxide Carbon Tetrahydride Dihydrogen oxide

76 Naming Ionic and Covalent CompoundsIs the compound Ionic or Covalent? Does the Compound have a Polyatomic Ion? Name using the polyatomic rules. Name the metal cation followed by the nonmetal anion ending in –ide. Name using the di, tri, tetra prefixes Ionic Covalent Yes No Does the compound contain a transition metal? Yes No Name using Roman Numerals to express the charge on the transition metal. No further steps necessary.

77 Acids and Bases Acid BaseA substance that produces hydrogen ion when dissolved in water The hydrogen is written first in the chemical formula Base A substance that produces hydroxide ion when dissolved in water The hydroxide is written second in the chemical formula

78 Naming Acids and Bases For an acid containing a hydrogen and an anion: use the prefix hydro and change the –ide of the nonmetal to –ic and add the word acid. Example HCl = Hydrogen Chloride is Hydrochloric Acid For an acid containing a polyatomic ion, name the anion after the polyatomic ion, changing the –ate to –ic or the –ite to –ous and add the word acid. HNO3 = Hydrogen Nitrate is Nitric Acid HNO2 = Hydrogen Nitrite is Nitrous Acid Name a base as you would a polyatomic ion Ca(OH)2  Calcium Hydroxide NaOH  Sodium Hydroxide

79 Naming Acids and Bases H2SO4 HF LiOH HBr H3PO4 Acetic acidCarbonic Acid Phophorus Acid Hydroiodic Acid Magnesium Hydroxide

80 Hydrates Compounds that have water incorporated into the structureName the compound as usual, but indicate the number of water molecules present using a numeric prefix MgCl2 x 7H2O = Magnesium Chloride heptahydrate CuSO4 x 5H2O CuCl2 x 2H2O Cobalt (II) Chloride Hexahydrate

81 What Are Your Questions?