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Chemical Expressions

Learn about chemical expressions and molecular formulas in chemistry, including subscripts, coefficients, and determining chemical formulas.

michaelperez
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Chemical Expressions

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  1. Chemical Expressions

  2. Molecular Expressions • Subscripts – indicate the number of atoms in the formula - Example NaC2H3O2 Contains: 1 Sodium atom 2 Carbon atoms 3 Hydrogen atoms 2 Oxygen atoms

  3. Subscripts (cont.) • Outside parenthesis – apply to all symbols inside the parenthesis Example: Al2(SO4)3 Contains: 2 Aluminum atoms 3 x 1 Sulfur atoms 4 x 3 Oxygen atoms

  4. Coefficients • Represent the number of molecules • Example 6 HCl 6 hydrochloric acid molecules 17 H2O 17 water molecules

  5. Compounds Combinations of Atoms

  6. Compounds • All molecules are electrically neutral • Positives combine with negatives • Positive ions are written first • Negative ions are written last • All elemental gases are diatomic except the noble gases • H2, N2, O2, F2, Cl2, Br2, I2 • Polyatomic ions – charged groups of atoms which remain intact and combine as a single ion

  7. Determining Chemical Formulas

  8. When determining the chemical formula for a compound one must consider: • Valence - Combining Capacity • Oxidation State – the charge an atom actually has as an ion, or the charge it appears to have when electrons are shared or transferred

  9. Rules for Oxidation State Types Example Oxidation # Free Elements Na, He, C 0 Hydrogen H+ 1+ except in metal hydrides LiH Oxygen O2- 2- except in peroxide 1- 1A Alkali Metals Na+ 1+ 2A Alkali Earth Ca2+ 2+

  10. Rules for Oxidation State (cont.) Types Example Oxidation # 7A or 17 Halogens F- 1- only when written last Monatomic ions Cu2+, Na+assigned oxidation # according to the rule that the sum of the ox. # in a cpd. = 0 Polyatomic ions SO42-the sum of the ox. # must equal the charge on the ion

  11. Naming Compounds(Nomenclature) • Binary Compounds – compounds composed of only two kinds of atoms • Salts – composed of metal (cation) and a nonmetal (anion)

  12. Binary Names Metal + Nonmetal name the metal use the stem name of the nonmetal with an “ide” ending insert roman numeral when there is more than one oxidation state for the metal

  13. Example 1: Potassium combines with Sulfur Ions: K+ S2- Formula: K2S Name: Potassium Sulfide

  14. Example 2: Zinc combines with Chlorine Ions: Zn2+ Cl- Formula: ZnCl2 Name: Zinc Chloride

  15. Example 3: Copper combines with Oxygen Ions: Cu+ or Cu2+ O2- Formula: Cu2O or CuO depends on the oxidation # of the Cu ion Name: Copper (I) Oxide or Copper (II) Oxide

  16. Zirconium with Iodine Formula: ?? Name: ?? Cr 6+ with Sulfur Formula: ?? Name: ?? Now You Try It! Determine the formula and the names for the following compounds

  17. Binary Names (cont.) Nonmetal + Nonmetal • name the cation first • name the anion with an “ide” ending • use prefixes to number the atoms when necessary mono – 1 di – 2 tri – 3 tetra – 4 penta – 5 hexa – 6 hepta – 7 octa – 8 nona – 9 deca – 10

  18. Example 4: Carbon combines with Oxygen Ions: C+4 02- Formula: CO2 Name: Carbon Dioxide

  19. Example 5: Phosphorous combines with Oxygen Ions: P+5 O2- Formula: P2O5 Name: Diphosphorous pentoxide Note: There are other combinations for these two elements

  20. Nitrogen 4+ with Oxygen Formula: ?? Name: ?? Phosphorous 3+ Bromine Formula: ?? Name: ?? Practice!!! Determine the formula and the names for the following compounds

  21. Nitrogen 4+ with Oxygen Formula: NO2 Name: Nitrogen dioxide Phosphorous 3+ with Bromine Formula: PBr3 Name: Phosphorous tribromide Answer!!!

  22. Ternary Compounds • Compounds containing with 3 kinds of atoms • Consist of a metal and a polyatomic ion • Name metal first (with roman numeral if needed) • Name polyatomic ion

  23. Other Polyatomic Ions “per”__”ate” “ate” + 1 oxygen “ate” suffix ion sheet ** “ite” suffix “ate” – 1 oxygen “hypo”__”ite” “ate” – 2 oxygens “ide” suffix hydroxide cyanide ferricyanide

  24. Example 6: Sodium combines with Carbonate Ions: Na+ CO32- Formula: Na2CO3 Name: Sodium Carbonate

  25. Example 7: Aluminum combines with Phosphite Ions: Al3+ PO33- Formula: AlPO3 Name: Aluminum Phosphite

  26. Now you try it!! Barium combines with Nitrate • Formula ?? • Name ??

  27. Try another one!! Lead combines with Sulfite (give all possible answers) Formulas – Names -

  28. Naming Acids • Acids are compounds containing H+ ions • Negative ions that end in “ate” • ___________ic acid • Negative ions that end in “ite” • ___________ ous acid • When no oxygen in the formula • hydro ___________ic acid

  29. Example 8: Hydrogen combines with Sulfate Ions: H+ SO42- Formula: H2SO4 Name: Sulfuric Acid

  30. Practice!! • Name this acid HCl

  31. Practice!! • Name this acid HCl hydrochloric acid

  32. Naming Bases • Bases are compounds containing OH- ions • Name the metal first followed by the word hydroxide Example: Ba(OH)2 Barium hydroxide

  33. An Older Naming Method • Traditionally Latin names were used for the metals • If the metal was in the higher oxidation state the suffix ‘ic’ was used on the latin root for the metal • If the metal was in the lower oxidation state the suffix ‘ous’ was used on the latin root for the metal

  34. A Few Latin Names Fe Ferrum Fe3+ ferric Fe2+ ferrous Cu Cupurum Cu2+ cupric Cu+ cuprous Pb Plumbum Pb4+ plumbic Pb2+plumbous

  35. Examples: FeCl3 Ferric Chloride PbO Plumbous Oxide CuSO4 Cupric Sulfate

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