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Understanding Oxidation Numbers in Chemical Compounds

Learn about assigning oxidation numbers to atoms in compounds, determining the charge of elements, and using numbers to track electrons. Practice assigning oxidation numbers in various compounds and ions.

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Understanding Oxidation Numbers in Chemical Compounds

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  1. Chemical Formulas and Compounds Oxidation Numbers

  2. Monday, November 26 • Take out a sheet of paper, title “Oxidation Numbers” • Take out your Naming Compounds sheet that you received before Thanksgiving holiday. • Hall Pass Policy: • 2 per NINE WEEKS • Document on Clipboard!

  3. Tuesday, November 27 • 1-15 Compound Naming Problems: Any Questions? • 16-30 = Homework Tonight • Must complete entire sheet to retake Quiz 1 &2 • Take out OXIDATION NUMBER notes from yesterday • Hall Pass Policy: • 2 per NINE WEEKS • Document on Clipboard!

  4. Nomenclature QUIZ 1 • Write the nomenclature: • Ammonium • Sulfate • Sulfite • Arsenate • Phosphate • Chlorate • Chlorite • Hydroxide • Tetra- • Penta- • Write the compound name: • CaBr2 • CoF3 • SnI4 • FeS • Ca(OH)2 • Write the formula: • Sodium Iodide • Calcium Chloride • Potassium Sulfide • Sodium Carbonate • Calcium Nitrite

  5. Nomenclature QUIZ 2 • Write the nomenclature: • Carbonate • Sulfate • NO2 ˉ • Nitrate • Phosphate • Hexa- • Nona- • H2SO4 • Hydrochloric acid • Nitric Acid • Write the compound name: • NaI • CaO • K2O • Ca(OH)2 • SO3 • Write the formula: • Sodium Hydroxide • Lead (II) Nitrate • Nitric Acid • Barium Dioxide • TricalciumDinitride

  6. Nomenclature QUIZ 3 • Write the nomenclature: • Carbonate • Ammonium • Hydroxide • NO3ˉ • Perchlorate • Sulfate • Tri- • Octa- • Chlorite • PO4 ³ˉ • Write the acid name: • HNO2 • HClO3 • H2SO4 • HCl • H2CO3 • Write the formula: • Iron (II) Nitrate • Sodium Fluoride • Carbon Monoxide • Potassium Sulfide • Iron (III) Oxide

  7. Oxidation Numbers • Oxidation Numbers • the charge that it would have if all the bonds were removed along with the electron pairs that were shared with the central atom. • Use to “keep track” of electrons • In general when assigning oxidation numbers, shared electrons are assumed to “belong” to the more electronegative atom in each bond Oxidation numbers of carbon and hydrogen in ethane (number does not refer to valance electrons)

  8. Oxidation Numbers • Assigning Oxidation Numbers • The atoms in a pure element have an oxidation number of zero • Monatomic ions have an oxidation number equal to the charge of the ion • The more-electronegative element in a binary compound is assigned a negative numberequal to the charge it would have as an anion. Likewise for the less-electronegative element. • Fluorine has an oxidation number of –1 in all of its compounds because it is the most electronegative element • Oxygen usually has an oxidation number of –2 • In peroxides, such as H2O2, oxygen’s oxidation number is –1 • In compounds with fluorine, such as OF2, oxygen’s oxidation number is +2

  9. Oxidation Numbers • Assigning Oxidation Numbers • Hydrogen has an oxidation number of +1 in all compounds containing elements that are more electronegative than it; it has an oxidation number of –1 with metals • The algebraic sum of the oxidation numbers of all atoms in an neutral compound is equal to zero • The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion • Although rules 1 through 7 apply to covalently bonded atoms, oxidation numbers can also be applied to atoms in ionic compounds similarly

  10. Oxidation Numbers • Oxidation Numbers • Sample Problem • Assign oxidation numbers to each atom in the following compounds or ions: • UF6 • H2SO4

  11. Oxidation Numbers • Oxidation Numbers • Sample Problem Solution • Place known oxidation numbers above the appropriate elements • Multiply known oxidation numbers by the appropriate number of atoms and place the totals underneath the corresponding elements • The sum of the oxidation numbers must equal zero unless there is a charge associated with the compound +5 2 +5 6

  12. Oxidation Numbers • Common Oxidation States of Nonmetals • Pg. 235

  13. Oxidation Numbers • Oxidation Numbers for Formulas and Names • Many nonmetals can have more than one oxidation number • These numbers can sometimes be used in the same manner as ionic charges to determine formulas (+ -) • What is the formula of a binary compound formed between sulfur and oxygen? • From the +4, +6 oxidation numbers of sulfur, you could predict that sulfur might form SO2 or SO3 • Remember: The more-electronegative element in a binary compound is assigned a negative numberequal to the charge it would have as an anion. Likewise for the less-electronegative element.

  14. Oxidation Numbers • Oxidation Numbers for Formulas and Names • Using oxidation numbers, the Stock system, introduced in the previous section for naming ionic compounds, can be used as an alternative to the prefix system for naming binary molecular compounds

  15. Practice Problems • Assign oxidation numbers to each atom in the following compounds or ions: • HF • CI4 • H2O • PI3 • CS2 • Na2O2 • H2CO3 • NO2ˉ

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