2013-08-04 Rules for Assigning B) Oxidation State Determination Oxidation State (O.S.)* 1. O.S. of an atom in pure element = 0 Oxidation and Reduction For an atom, electrons can be lost or gained during a 2. O.S. of monoatomic ion = charge chemical reaction. 3. O.S. of Oxygen (O) is -2 in most of its covalent and ionic compounds (-1 in peroxides). If electrons are lost: OXIDATION The state becomes more positive 4. O.S. of H is +1 when combined with a non-metal 5. O.S. of H is -1 when combined with a metal If electrons are gained: REDUCTION The state becomes more negative 6. O.S. of Fluorine (F) is -1 in compounds 7. The sum of O.S. is 0 in compounds Oxidation State (O.S.) or Oxidation Number (O.N.) Number of electrons lost or gained during a chemical 8. The sum of O.S. equals charge in ions change * A compilation from different textbooks Elements with Fixed Oxidation States (O.S.)* Instead of memorizing elements that show different O.S., remember those that have a fixed one: Group 1 (IA) elements: Always +1 Group 2 (IIA) elements: Always +2 Aluminum, Al, and Scandium, Sc: Always +3 Zinc, Zn, and Cadmium, Cd: Always +2 Silver, Ag: Always +1 * A compilation from different textbooks 1 2013-08-04 OXIDATION STATE DETERMINATION EXERCISES Assign oxidation state (O.S.) to each element in the following compounds: a) SO3 i) CrCl3 2- 2- b) SO3 j) CrO4 2- c) KMnO4 k) Cr2O7 d) MnO2 l) HClO4 e) HNO3 m) HClO3 f) S8 n) HClO2 g) CH2Cl2 o) HClO h) SCl2 p) K2SO4 2 2013-08-04 C) A Nomenclature Proposal MORE GENERAL OBSERVATIONS Problematic of Nomenclature Coverage in Textbooks • Flow charts of various complexities (relatively often!) Flow charts, rules, … and tables, tables, tables … (Memorization!) ü From 3-box flow charts to 14-box ones GENERAL OBSERVATIONS • Link with acid/base concepts (sometimes, but rarely!) • Appears in chapters 2 or 3 of textbooks (often!) ü So, it is to be covered “at once”; as a single topic. ü Explanations on “hydrogen -ate/ite” ions (sometimes!) • Appears in end-of-textbook appendices (sometimes!) • Naming of hydrated salts (sometimes!) ü Very brief coverage, condensed guidelines • The “-ide”, “-ate”, and “-ite” cases (how are they • Tables of common ions (always!) linked and how they differ?) ü Monoatomic and polyatomic ions ü (and to the “-ic” and “-ous” ones too!) v Separated or altogether! • The Stock system (not always mentioned!) ü Oxidation states (charges) of metals (in figures or tables) Language of Chemistry: Important Elements to Know Part 1: Elements and Periodic Table Elements (Symbol/Name) to Know (I) Elements (Symbol/Name) to Know (II) 1. H Hydrogen 13. Al Aluminum 25. Mn Manganese (NOT Mg) 38. Sr Strontium 2. He Helium 14. Si Silicon 26. Fe Iron 47. Ag Silver 3. Li Lithium 15. P Phosphorus (from Latin Ferrum) (from Latin Argentum) 4. Be Beryllium (NOT Phosphorous) 27. Co Cobalt (NOT Copper) 50. Sn Tin 5. B Boron (NOT Potassium) 28. Ni Nickel (NOT N) (from Latin Stannum) 6. C Carbon (NOT Ca) 16. S Sulfur (or Sulphur) 29. Cu Copper (NOT Co) 53. I Iodine 7. N Nitrogen (NOT Ni) 17. Cl Chlorine (NOT clorine) (from Latin Cuprum) 56. Ba Barium 8. O Oxygen 18. Ar Argon (NOT Arsenic) 30. Zn Zinc 78. Pt Platinum 9. F Fluorine 19. K Potassium (NOT P) 31. Ga Gallium 79. Au Gold (from Latin Aurum) (NOT Flourine) (from Latin Kalium) 32. Ge Germanium 80. Hg Mercury 10. Ne Neon 20. Ca Calcium (NOT Carbon) 33. As Arsenic (NOT Ar) (from Latin Hydrargyrum) 11. Na Sodium 21. Sc Scandium 34. Se Selenium (NOT S) 82. Pb Lead (from Latin Natrium) 22. Ti Titanium 35. Br Bromine (from Latin Plumbum) 12. Mg Magnesium (NOT Mn) 23. V Vanadium 36. Kr Krypton 92. U Uranium 24. Cr Chromium 3 2013-08-04 Types of Chemical Compounds Language of Chemistry: Part 2: Binary Acids and Compounds Acid-Base Models: 1. A metal + a non-metal (e.g. NaCl) Brønsted-Lowry: + Leads to ionic compounds! Acids are H donors, Bases are H+ acceptors (need at least 1 atom with a lone pair). 2. A non-metal + another non-metal (e.g. CO2) - + Leads to covalent (or molecular) compounds! HF(aq) ⇌ F (aq) + H (aq) Acid conj. base + - NH3(aq) + H2O(l) ⇌ NH4 (aq) + OH (aq) Base conj. acid Binary Covalent Compounds List of Binary Acids and Acids Binary Acids, Related Ions, and Covalent Compounds Covalent Covalent Acid Acid Related Ion Compound Compound Formula Name Ion Name Formula Name Groups 16/17 elements combined with hydrogen give binary covalent compounds in the gas state (g). HF(aq) Hydrofluoric acid F- Fluoride HF(g) Hydrogen fluoride Example: HCl(g) is Hydrogen chloride HCl(aq) Hydrochloric acid Cl- Chloride HCl(g) Hydrogen chloride HBr(aq) Hydrobromic acid Br- Bromide HBr(g) Hydrogen bromide Group 16/17 elements combined with hydrogen give binary acids when dissolved in water (aq). HI(aq) Hydroiodic acid I- Iodide HI(g) Hydrogen iodide S2- Sulfide Example: HCl(aq) is Hydrochloric Acid H2S(aq) Hydrosulfuric acid H2S(g) Dihydrogen sulfide HS- Hydrogen sulfide ® François Gauvin 2005 Nomenclature Names of Binary Binary Compounds Ionic Compounds 1. Name the metal first. (BINARY: made of only two elements) If the metal can have more than one oxidation state, the latter is specified by a Roman numeral between Ionic or Covalent Compound? parentheses (Stock System). There is NO SPACE BETWEEN METAL NAME AND OPENING Compound contains a metal Compound contains PARENTHESIS. or ammonium ion (NH +) only nonmetals 4 Example: Cu+ and Cu2+ (copper cations) Cu+ is copper(I) ion; NOT copper (I) Name as an Name as a Cu2+ is copper(II) ion; NOT copper (II) Ionic Compound Covalent compound 4 2013-08-04 Names of Binary Example 1 Ionic Compounds Name the following binary compound: 2. Then name the non-metal (i.e. the anion) FeCl2 by changing the ending of the non-metal Fe (metal) with Cl (non-metal) name to -ide (-ide suffix). → Ionic compound Fe is iron (no fixed O.S.); Cl is chlorine. Refer to parent binary acid for ion name. Name non-metal with –ide suffix: chloride. Oxidation state of metal: For example: Chloride is from Hydrochloric acid, HCl, so it is Cl– Hydrochloric acid, HCl(aq) leads to In this compound, O.S.(Fe) is +2 → iron(II) chloride (Cl-) ion So the name is Iron(II) chloride. Naming Binary Example 2 Covalent Compounds Name the following binary compound: Compounds made of two PF5 non-metallic elements Both P and F are non-metals. the more “metallic” element is No hydrogen in compound listed first → Covalent compound (to the left or below); Most “metallic” is Phosphorus, The other element is treated Fluorine is treated as an anion → fluoride. as an anion; Use prefixes to indicate the number of atoms. Prefixes are used to specify So the name is Phosphorus pentafluoride. the number of atoms Example 3 Example 4 Give the formula of the following binary compound: Give the formula of the following binary compound: Calcium Oxide Diphosphorus pentasulfide Calcium is a metal → Ionic compound Its symbol is Ca. Phosphorus is a non-metal. Its symbol is P. Its oxidation state is fixed at +2 (Group 2 element). Sulfide is the anion of sulfur, S; another non-metal. 2+ So its charge is 2+, Ca . Oxide is the anion of oxygen, O; the non-metal. Both elements of this compound are non-metals. Its charge is 2-, O2- (so O.S. of oxide ion is -2). → Covalent compound Combine the two ions in order to cancel the positive and negative Prefixes in the compound name literally tell us what the charges. formula is: In this case, the 2+ charge of Ca cancels the 2- charge of O. Therefore, the formula should contain 1 Ca with 1 O. Di- means 2 and penta- means 5. So the formula is CaO. So the formula is P2S5. 5 2013-08-04 Example 5 Language of Chemistry: Give the formula of the following binary compound: Part 3: Oxoacids (HaZbOc) and Polyatomic Ion Compounds Chromium(III) oxide Case of Sulfuric Acid (loss of first H+ ion): Chromium is a metal (symbol is Cr) → Ionic compound. Its oxidation state is NOT fixed, but its value is +3 as - + 3+ H2SO4(aq) → HSO4 (aq) + H (aq) stated by the Roman numeral in the name, Cr cation. Acid conj. base Oxide is the anion of oxygen, O; the non-metal. 2- Its charge is 2-, O (so O.S. of oxide ion is -2). HSO - ANION 4 Combine the two ions in order to cancel the positive and negative + charges. Case of sulfuric Acid (loss of second H ion): In this case, 2 Cr3+ ions (total charge 6+) would cancel the charge of 3 O2- ions (total charge 6-). - 2- + HSO4 (aq) → SO4 (aq) + H (aq) Therefore, the formula should contain 2 Cr with 3 O. Acid conj. base 2- So the formula is Cr2O3. SO4 ANION Language of Chemistry: Nomenclature of Nomenclature of Polyatomic Ion Compounds Polyatomic Ion Compounds 1. Name the metal (or ammonium ion) first. If the metal can have more than one Binary or Polyatomic ion Compound? oxidation state, the latter is specified by a Roman numerals between parentheses (Stock System). There is NO SPACE Compound contains only Compound contains MORE BETWEEN METAL NAME AND OPENING TWO elements than TWO elements (including O) PARENTHESIS. Name as a Name as a Polyatomic 2. Name the anion from its parent oxoacid, Binary Compound Ion Compound using the –ate or –ite suffix depending on the name of the parent oxoacid (see next slide).