Atoms, Molecules and Ions Chapter 2 Summary Atoms Subatomic Particles Isotopes Periodic Table Classifications Diatomic Elements Ions Naming Compounds STM Image of Graphite Scanning Tunneling Microscopy What are Elements Composed of? Not until 1803 was there enough scientific evidence to show that matter is composed of indivisible particles. In 1803, John Dalton proposed the Atomic Theory. Dalton?s Atomic Theory Matter is composed of indivisible particles called atoms. Atoms of the same element are identical and have the same properties. Atomic Theory Compounds are composed of atoms of different elements combined in simple, whole number ratios. During chemical reactions, atoms rearrange into different combinations. Laws of Chemical Combination Dalton?s Atomic Theory helps explain: Law of Constant Composition e.g. H2 and O2 combine to form water in a mass ratio of 1 to 8 Law of Conservation Mass (Matter) When 1 g of H combines with 8 grams of O, 9 grams of H2O form. 2H2 + O2 ? 2H2O Conservation of Mass Since atoms are just rearranged during chemical reactions, there is no loss or gain of mass. A01-2-20.mov Mass is Conserved Zn(s) + 2HCl(aq) ? ZnCl2(aq) + H2(g) Law of Multiple Proportions The ratios of oxygen to carbon in the two compounds below are related by a whole number (2). O/C mass Ratio Carbon Monoxide, CO 1.33/1 Carbon Dioxide, CO2 2.67/1 Composition of the Atom Subatomic Particles Electron Proton Neutron 1897 (Thomson)- Electron discovered Negatively charged particle. (-1) Electron (e-) - 1897 Charge to Mass = 1.76 x 108 coulombs/gram ? - ? Robert Millikan Charge of an Electron (1.6 x 10-19 C) Calculate Mass of Electron Charge of an Electron = 1.6 x 10-19 C Charge to Mass = 1.76 x 108 C/gram Calculate Mass of Electron Charge of an Electron = 1.6 x 10-19 C Charge to Mass = 1.76 x 108 C/gram Mass of Electron = 9.09 x 10-28 g Known today to 6 sig figs: 9.10939 x 10-28 g Composition of the Atom (Subatomic Particles) Since atoms are neutral, it was assumed that the atom must also be composed of positively charged particles. Plum Pudding Model: Not Correct Not Correct! Rutherford?s Experiment Rutherford?s Experiment Micro Nuclear Model of the Atom 99.95% of Atomic Mass Subatomic Particles Subatomic Particles Particle Mass Relative Charge Proton 1.673x10-24 g (1.0073 amu) +1 Neutron 1.675x10-24 g (1.0087 amu) 0 Electron 9.109x10-28 g (5.486x10-4 amu) -1 1 amu = 1.66054x10-24 g Atomic Number Atomic Number = # Protons The atomic number for an element is the number above the element symbol in the periodic table. 6 C 12.011 SubatomicParticles In a neutral atom, the number of electrons equals the number of protons. The number of neutrons can vary. Atoms of the same element with different numbers of neutrons are called isotopes. Isotopes of Carbon Most carbon atoms contain 6 protons and 6 neutrons. Some carbon atoms have 7 or 8 neutrons. Mass Number Mass number = # protons + #neutrons What is the mass number for a C atom with: 6 neutrons? 8 neutrons? Isotope Symbols Isotope symbols are used to show the number of neutrons in an atom. Mass number Atomic number Isotopes of Hydrogen Group Quiz 1 piece of paper Write TA name at top Write full names of all group members If you are not in a group yet, write the day and time you have lab (eg. M 2:40pm) Group Quiz Write the isotope symbol for each isotope. 19 protons and 20 neutrons Mass number = 238 and #neutrons= 146 The Periodic Table The Long Periodic Table The Periodic Table The periodic classification of elements was developed in 1869 by Dmitri Mendeleev. Elements are arranged in rows of increasing atomic number so that elements in the same column have similar chemical and physical properties, or they vary in a regular fashion. The Periodic Table Rows are called Periods Columns are called Groups or Families The Periodic Table Table 2.3 Group IA - Alkali Metals (except H) Group 2A - Alkaline Earth Metals Group 6A - Chalcogens Group 7A - Halogens Group 8A - Noble Gases The Periodic Table The elements can also be classified as metals, nonmetals or metalloids. Metals - left of the stair-step line. Nonmetals - Right of the stair-step. Metalloids - Lie on the stair-step. The Periodic Table Metals, Nonmetals, and Metalloids Molecular Elements A molecule is a group of atoms chemically bonded. Molecular elements are composed of only one type of atom. S8 P4 Cl2 Diatomic Elements Diatomic elements are composed of molecules that contain two like atoms. Know these: H2 N2 O2 F2 Cl2 Br2 I2 The 7 Elements that are Diatomic molecules Ions Ions are atoms or groups of atoms that have an electrical charge. Loss of electrons results in cations: Na ?? Na+ + e- Gain of electrons results in anions: Cl + e- ? Cl- Common Monatomic Ions Ag+ Cd2+ Zn2+ Ion_Charges Figure 2.22 in your text Ions Predict the charge on each monatomic ion: Ca? O? Br? Cs? Ions Predict the charge on each monatomic ion: Ca2+ O2? Br? Cs+ Ions How are cations and anions named differently? Ca2+ calcium ion O2? oxide ion Br? bromide ion Cs+ cesium ion Polyatomic Ions Polyatomic ions are like molecules but with a charge: Examples: OH?, NH4+, CO32?, PO43? See Polyatomic Ion Handout in ?Lecture Handouts? folder in ?COURSE DOCUMENTS? Look for Patterns: NO3? nitrate ion NO2? nitrite ion SO42? sulfate ion SO32? sulfite ion ClO3? chlorate ion ClO2? chlorite ion Formation of Ionic Compounds VD02_007.mov Ionic Compounds Ionic compounds are composed of cations and anions. Most consist of a metal cation and a nonmetal anion or polyatomic ion. Examples: NaCl Cu(OH)2 Ca3(PO4)2 Ionic Compounds Compounds are neutral, so the ion charges add to zero. Ca3(PO4)2 Writing Ionic Formulas What is the formula for: Aluminum hydroxide Calcium nitride Magnesium oxide Group Work What is the formula for magnesium nitrate magnesium nitrite sodium sulfate sodium sulfite Naming Binary Ionic Compounds When Metal forms a Single Cation Simply name the cation first and then the anion. The monatomic anion name retains the root name and adds the suffix -ide. Examples: MgCl2: Magnesium chloride Li3N: Lithium nitride Naming Ionic Compounds When an ion is a polyatomic ion, the name of the ion is used in the name. Examples: AgNO3: Silver nitrate Ca3(PO4)2: Calcium phosphate Naming Binary Ionic Compounds When Metal forms Several Cations: Stock System 1. Determine the charge on the metal from the formula: eg. CuO (Cu2+) Cu2O (Cu+) 2. Write the cation name followed by the roman numeral positive charge in parentheses, and then the name of the anion with the -ide ending. Copper(II) oxide Copper(I) oxide Naming Binary Ionic Compounds When Metal forms a Several Cations: Classical System 1. Determine the charge on the metal from the formula: eg. CuO (Cu2+) Cu2O (Cu+) 2. Write the cation name with the suffix (-ic or -ous) that corresponds to the charge (see T 2.4), and then anion name with the -ide ending. Cupric oxide Cuprous oxide Group Work Name the following compounds using the Stock System. FeS Fe2S3 PbO2 PbO CrO3 Group Work Write the formula for the following Copper(II) nitrate Iron(III) phosphate Types of Substances Which of the following are composed of ions? MgCl2 CO2 Cl2 Li3N Which of the following are composed of ions? MgCl2 magnesium chloride CO2 carbon dioxide Cl2 chlorine Li3N lithium nitride Molecular Compounds Molecular compounds are usually composed of nonmetals and are NOT composed of ions. Examples: N2O, NO, NO2, N2O4, N2O5 CO2, CO, SF4, SF6 Naming Molecular Compounds Greek prefixes are used to show the number of each element in the compound. CCl4 is named carbon tetrachloride. Prefixes: 1 mono 5 penta 2 di 6 hexa 3 tri 7 hepta 4 tetra 8 octa Common Molecular Compounds that Retain Old Name Water H2O Ammonia NH3 Hydrogen peroxide H2O2 Acids Some molecular substances give acidic properties when dissolved in water. When they are dissolved in water we call them acids. For example: HCl(g) - hydrogen chloride HCl(aq) - hydrochloric acid Binary Acids Binary acids are composed of hydrogen and a single nonmetal. HF hydrofluoric acid HCl hydrochloric acid HBr hydrobromic acid HI hydroiodic acid H2S hydrosulfuric acid Oxyacids Oxyacids are composed of hydrogen and an oxyanion (oxygen containing polyatomic ion). Examples: HNO3 Nitric acid HNO2 Nitrous acid H2SO4 Sulfuric acid H2SO3 Sulfurous acid Practice Naming Compounds For extra practice: See Nomenclature Worksheet on Blackboard website. You will not have to name organic compounds (2.9)
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