Chapter 2: Atoms, Molecules, and Ions Renee Y. Becker Valencia Community College CHM 1045
Dalton’s Atomic Theory • Elements are made of tiny particles called atoms. • Each element is characterized by the mass of its atoms. Atoms of the same element have the same mass, but atoms of different elements have different masses. • Chemical reactions only rearrange the way atoms are combined; the atoms themselves are unchanged.
The Structure of Atoms • Cathode-Ray Tube (Thomson, 1856–1940): Cathode rays consist of tiny negatively charged particles, now called electrons.
The Structure of Atoms • Deflection of electron depends on three factors: • Strength of electric or magnetic field • Size of negative charge on electron • Mass of the electron • Thomson calculated the electron’s charge to mass ratio as 1.758820 x 108 Coulombs per gram.
The Structure of Atoms • Oil Drop Experiment (Millikan, 1868–1953): Applied a voltage to oppose the downward fall of charged drops and suspend them. • Voltage on plates place 1.602176 x 10-19 C of charge on each oil drop. • Millikan calculated the electron’s mass as 9.109382 x 10-28 grams.
The Structure of Atoms • Discovery of Nucleus:Rutherford irradiated gold foil with a beam of alpha particles to search for positive charged particles. Most of the particles passed through but some were deflected at large angles, why?
Periods: Seven horizontal rows Groups: 18 vertical columns, based on similar chemical properties
The Structure of Atoms Standard Format
The Structure of Atoms • Isotopes: Atoms with identical atomic numbers, but different mass numbers. • Average Isotopic Mass: A weighted average of the isotopic masses of an element’s naturally occurring isotopes. • Atomic Mass: A weighted average of the isotopic masses of an element’s naturally occurring isotopes.
Example 1: Periodic Table What are the atomic numbers for the following elements? • Copper • Sodium • Sulfur • Oxygen
Example 2: Periodic Table What are the atomic masses for the following elements? • Iron • Magnesium • Bromine • Xenon
Example 3: Periodic Table What are the mass numbers for the following elements? • Chlorine • Nitrogen • Carbon • Zinc
75 75 Se Se 34 34 Example 4: The Structure of Atoms • The isotope is used medically for diagnosis of pancreatic disorders. How many protons, neutrons, and electrons does an atom of have?
Example 5: The Structure of Atoms • An atom of element X contains 47 protons and 62 neutrons. Identify the element, and write the symbol for the isotope in the standard format.
35 37 Cl Cl 17 17 Example 6: The Structure of Atoms • Chlorine has two naturally occurring isotopes: with an abundance of 75.77% and an isotopic mass of 34.969 amu, and with an abundance of 24.23% and an isotopic mass of 36.966 amu. What is the atomic mass of chlorine?
Atoms, Molecules, and Ions • Covalent Bonding (Molecules): The most common type of chemical bond is formed when two atoms share some of their electrons. (non-metal -- non-metal)
Atoms, Molecules, and Ions Naming Binary Molecular Compounds: • The more cationlike element uses its elemental name. • The more anionlike element substitutes the second half of its elemental name with –ide. • Use the Greek prefixes to express the number of each element present.
Greek Prefixes Nona- 9 Deca- 10
Example 8: Atoms, Molecules, and Ions Examples: CO carbon monoxide CO2 carbon dioxide SF4 sulfur tetrafluoride Name: NCl3 P4O6 S2F2 Write formulas: Disulfur dichloride Iodine monochloride Nitrogen trioxide
Atoms, Molecules, and Ions • Ionic Bonding (Ionic Solids): These are formed by a transfer of one or more electrons from one atom to another. (metal -- non-metal)
Example 9 Which of the following drawings represents an ionic compound? Molecular compound?
Atoms, Molecules, and Ions Naming Binary Ionic Compounds: • Identify the positive ion and then the negative ion. • The positive ion uses its elemental name. • The negative ion substitutes the second half of its elemental name with –ide. • Do not use Greek prefixes such as mono–, di–, or tri–. • Use roman numerals for transition metals
Example 10: Name • NaCl • MgS • Ba3N2 • CaO • K2S • FeCl2 • FeCl3 • CrO2 • ZnCl2 • V2O3
Example 11: Draw • Calcium chloride • Copper (II) sulfide • Sodium nitride • Silver bromide • Nickel (II) phosphide • Cesium oxide • Strontium iodide • Cobalt (I) sulfide
Atoms, Molecules, and Ions • Naming Ionic Compounds Containing Polyatomic Ions : • Same as binary ionic compounds • But use the name provided for the polyatomic ion
Example 12: Atoms, Molecules, and Ions • Examples • CaCO3 Calcium carbonate • FeCrO4 Iron(II) chromate • KOH Potassium hydroxide Name: Write Formulas: Ba3(PO4)2 Iron(II) permanganate Na2SO4 Cesium nitrate Sn(ClO4)4 Zinc acetate
Example 13: Which of the following is a covalent compound? • NaCl • NaOH • H2O • AlCl3
Atoms, Molecules, and Ions Acid: A substance that provides H+ ions in H2O Base: A substance that provides OH- in H2O Oxoacid: Contain oxygen and hydrogen and another element
Atoms, Molecules, and Ions Naming acids: When acid is dissolved in water gives one or more H+ and a polyatomic oxoanion, (has to have (aq)) Name of acid is based on the oxoanion Get pink sheet out!!
Example 14: Atoms, Molecules, and Ions Name the following acids: (a) HBrO3(aq) (b) HCN(aq)(c) HIO3(aq)(d) HMnO4(aq)(e) H2CrO4(aq)
Balancing Chemical Equations • A balanced chemical equation represents the conversion of the reactants to products such that the number of atoms of each element is conserved. Calcium carbonate calcium oxide + carbon dioxide CaCO3(s) CaO(s) + CO2(g)
Balancing Chemical Equations • Balancing Equations: write unbalanced equation A2 + B2 A2B • Use coefficients to indicate how many formula units are required to balance the equation: 2 A2 + B22 A2B
Balancing Chemical Equations • Method 1 (suggested) • Balance those atoms which occur in only one compound on each side • Balance remaining atoms • Reduce coefficients to smallest whole integers • Check your answer
Balancing Chemical Equations • Method 2 • Identify most complex compound • Balance this compound by placing 1 before it • Balance remaining compounds using fractions • Multiply fractions to obtain integers
Example 15: Balancing Chemical Equations • Balance the following equations C6H12O6 C2H6O + CO2 Fe + O2 Fe2O3 NH3 + Cl2 N2H4 + NH4Cl KClO3 + C12H22O11 KCl + CO2 + H2O