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Chapter 5: Molecules and Compounds

Chapter 5: Molecules and Compounds. Salt Sodium – shiny, reactive, poisonous Chlorine – pale yellow gas, reactive, poisonous Sodium chloride – table salt Sugar Carbon – pencil or diamonds Hydrogen – flammable gas Oxygen – a gas in air Combine to form white crystalline sugar.

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Chapter 5: Molecules and Compounds

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  1. Chapter 5: Molecules and Compounds Salt Sodium – shiny, reactive, poisonous Chlorine – pale yellow gas, reactive, poisonous Sodium chloride – table salt Sugar Carbon – pencil or diamonds Hydrogen – flammable gas Oxygen – a gas in air Combine to form white crystalline sugar

  2. 5.2 Compounds Display Constant Composition FIGURE 5.4A mixture  This balloon is filled with a mixture of hydrogen and oxygen gas. The relative amounts of hydrogen and oxygen are variable. FIGURE 5.5A chemical compound  This balloon is filled with water, composed of molecules that have a fixed ratio of hydrogen to oxygen. (Source:JoLynn E. Funk.)

  3. Compounds Display Constant Composition If we decompose water by electrolysis, we find 16.0 grams of oxygen to every 2.00 grams of hydrogen. Water has a constant Mass Ratio of Oxygen to Hydrogen of 8.0.

  4. Why do Compounds ShowConstant Composition the smallest piece of a compound is called a molecule every molecule of a compound has the same number and type of atoms since all the molecules of a compound are identical, every sample will have the same ratio of the elements since all molecules of a compound are identical, every sample of the compound will have the same properties

  5. Formulas Describe Compounds H2O C12H22O11 Water: 2 Hydrogen atoms and 1 Oxygen atom Sucrose (table sugar): 12 atoms of Carbon, 22 atoms of Hydrogen and 11 atoms Oxygen

  6. If the molecule is an ion a superscript number represents the charge of the molecule A number in front of a molecule means that you have more than one molecule; it is often referred to as coefficient 4 Mg(NO3) 2 A subscript number after a parenthesis means that all the atoms in the parenthesis are present in that molecule multiple times. A subscript number after an element means that you have more than 1 atom for that element

  7. The specific order for listing nonmetal elements in a chemical formula is shown in Table 5.1. There are a few historical exceptions in which the most metallic element is named first, such as the hydroxide ion, which is written as OH−.

  8. Classifying Materials atomic elements = elements whose particles are single atoms molecular elements = elements whose particles are multi-atom molecules molecular compounds = compounds whose particles are molecules made of only nonmetals ionic compounds = compounds whose particles are cations and anions

  9. Molecular Elements Certain elements occur as 2 atom molecules Rule of 7’s there are 7 common diatomic elements find the element with atomic number 7, N make a figure 7 by going over to Group 7A, then down don’t forget to include H2 VIIA 7 H2 N2 O2 F2 Cl2 Br2 I2

  10. Molecular Compounds two or more nonmetals smallest unit is a molecule

  11. Ionic Compounds metals + nonmetals no individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units

  12. Molecular View of Elements and Compounds

  13. Step1 - Common Names - Exceptions • H2O = water, steam, ice • NH3 = ammonia • CH4 = methane • NaCl = table salt • C12H22O11 = table sugar

  14. Step 2 - Classifying Compounds • Compounds containing a metal and a nonmetal = binary ionic • Type I and II • Compounds containing a polyatomic ion = ionic with polyatomic ion • Compounds containing two nonmetals = binarymolecular compounds • Compounds containing H and a nonmetal = binary acids • Compounds containing H and a polyatomic ion = oxyacids

  15. Step 3 - Formula-to-NameRules for Ionic • Made of cation and anion • Name by simply naming the ions • If cation is: • Type I metal = metal name • Type II metal = metal name(charge) • Polyatomic ion = name of polyatomic ion • If anion is: • Nonmetal = stem of nonmetal name + ide • Polyatomic ion = name of polyatomic ion

  16. Monatomic Nonmetal Anion • determine the charge from position on the Periodic Table • to name anion, change ending on the element name to –ide

  17. Metal Cations • Type I • metals whose ions can only have one possible charge • IA, IIA, (Al, Ga, In) • determine charge by position on the Periodic Table • IA = +1, IIA = +2, (Al, Ga, In = +3) • Type II • metals whose ions can have more than one possible charge • determine charge by charge on anion How do you know a metal cation is Type II? its not Type I !!!

  18. Type I Binary Ionic Compounds • Contain Metal Cation + Nonmetal Anion • Metal listed first in formula & name • name metal cation first, name nonmetal anion second • cation name is the metal name • nonmetal anion named by changing the ending on the nonmetal name to -ide

  19. Type II Binary Ionic Compounds • Contain Metal Cation + Nonmetal Anion • Metal listed first in formula & name • name metal cation first, name nonmetal anion second • metal cation name is the metal name followed by a Roman Numeral in parentheses to indicate its charge • determine charge from anion charge • Common Type II cations in Table 5.5 • nonmetal anion named by changing the ending on the nonmetal name to -ide

  20. Some Common Polyatomic Ions

  21. Step 3- Formula-to-NameRules for Molecular • we will not learn the rules for molecular compounds with more than 2 elements • for binary molecular: • name first nonmetal • then name second nonmetal with ide ending • then give each name a prefix to indicate its subscript in the formula

  22. Binary Molecular Compounds of 2 Nonmetals • Name first element in formula first • use the full name of the element • Name the second element in the formula with an -ide • as if it were an anion, however, remember these compounds do not contain ions! • Use a prefix in front of each name to indicate the number of atoms • Never use the prefix mono- on the first element

  23. Subscript - Prefixes • 1 = mono-; • not used on first nonmetal • 2 = di- • 3 = tri- • 4 = tetra- • 5 = penta- • 6 = hexa- • 7 = hepta- • 8 = octa- • drop last “a” if name begins with vowel

  24. Acids • Contain H+1 cation and anion • in aqueous solution • Binary acids have H+1 cation and nonmetal anion • Oxyacids have H+1 cation and polyatomic anion

  25. Formula-to-NameAcids • acids are molecular compounds that often behave like they are made of ions • All names have acid at end • Binary Acids = hydro prefix + stem of the name of the nonmetal + ic suffix • Oxyacids • if polyatomic ion ends in –ate = name of polyatomic ion with –ic suffix • if polyatomic ion ends in –ite = name of polyatomic ion with –ous suffix

  26. Formula-to-Name Flow Chart

  27. Writing the Formulas from the Names • For binary molecular compounds, use the prefixes to determine the subscripts • For Type I, Type II, Ternary Compounds and Acids • Determine the ions present • Determine the charges on the cation and anion • Balance the charges to get the subscripts

  28. Compounds that Contain Ions • compounds of metals with nonmetals are made of ions • metal atoms form cations, nonmetal atoms for anions • compound must have no total charge, therefore we must balance the numbers of cations and anions in a compound to get 0 charge • if Na+ is combined with S2-, you will need 2 Na+ ions for every S2- ion to balance the charges, therefore the formula must be Na2S

  29. Writing Formulas for Ionic Compounds • Write the symbol for the metal cation and its charge • Write the symbol for the nonmetal anion and its charge • Charge (without sign) becomes subscript for other ion • Reduce subscripts to smallest whole number ratio • Check that the sum of the charges of the cation cancels the sum of the anions

  30. Write the formula of a compound made from aluminum ions and oxide ions • Write the symbol for the metal cation and its charge • Write the symbol for the nonmetal anion and its charge • Charge (without sign) becomes subscript for other ion • Reduce subscripts to smallest whole number ratio • Check that the total charge of the cations cancels the total charge of the anions Al+3 column IIIA O2- column VIA Al+3 O2- Al2 O3 Al = (2)∙(+3) = +6 O = (3)∙(-2) = -6

  31. Formula Mass • the mass of an individual molecule or formula unit • also known as molecular mass or molecular weight • sum of the masses of the atoms in a single molecule or formula unit • whole = sum of the parts! mass of 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu

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