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Determining Formulas The Criss-Cross Method

Determining Formulas The Criss-Cross Method. Examples Na +1 + O -2  Ca +2 + P -3  C +4 + O -2 . Na 2 O. Ca 3 P 2. C 2 O 4  reduced to CO 2. Naming Compounds. Chemical Nomenclature --> system used to name chemical substances.

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Determining Formulas The Criss-Cross Method

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  1. Determining FormulasThe Criss-Cross Method • Examples • Na+1 + O-2 • Ca+2 + P-3  • C+4 + O-2  Na2O Ca3P2 C2O4  reduced to CO2

  2. Naming Compounds • Chemical Nomenclature--> system used to name chemical substances. • The Name of a compound indicates the composition of the substance. From the name one can deduce a chemical formula.

  3. Naming Binary Compounds • The first element is named as usual but only a stem of the second is used followed by the suffix “ide” • For example: MgCl2 is Magnesium chloride : Al2O3 is Aluminum Oxide • The Chlorine and Oxygen must change their suffix from “ine” and “ygen” to “ide” !

  4. Naming Compounds • Try these! • NaCl • Li3N • MgI2 Sodium Chloride Lithium Nitride Magnesium Iodide

  5. Stock System for Transitional Metals • A compound that contains a transitional metal must be named so that the oxidation # of the metal is identified. • A Roman numeral is placed after the metal. It represents the oxidation # of the metal. Ex. FeCl3 Iron (III) Chloride CuCl2  Copper (II) Chloride

  6. Assigning Oxidation # Transitional Metals • The total charge on any compound or molecule is always equal to zero. • To determine unknown oxidation #s, add up the oxidation #s of the Cation and Anion and set them equal to zero. (Create an algebra formula and solve for X.) Example Cr2O3 total charge = 0 Cr = x , O = -2 Formula 2x + 3(-2)= 0  2x-6= 0 x= +3 Cr= +3

  7. Naming Transitional Metal Compound Name These, • FeCl2 • CrO2 • NiP Iron(II) Chloride Chromium(IV) Oxide Nickel(III) Phosphide

  8. Naming compounds that contain Poly-atomic ions • Identify the formula using Criss-Cross method. • Name the cation (metal) 1st . If a transitional metal determine the charge and assign the Roman numeral that is equivalent to the charge. • Name the poly-atomic ion using its normal name. Ex. Calcium + Nitrate  Calcium Nitrate Ca+2 + (NO3) -1  Ca(NO3)2

  9. Naming compounds that contain Poly-atomic ions Name These, • Ba3(PO4)2 • CrSO4 • W(OH)3 Barium Phosphate Chromium(II) Sulfate Tungsten(III) Hydroxide

  10. Naming Molecules(the old system) • If two non-metals are bonded covalently, the name can be shown using prefixes. • The number of atoms for each element in a molecule is usually indicated by the prefix: • mono - 1 atom - hexa - 6 atoms • di - 2 atoms - hepta - 7 atoms • tri - 3 atoms - octa - 8 atoms • tetra - 4 atoms • penta - 5 atoms

  11. Naming Molecules • Examples: • nitrogen dioxide is NO2 • dinitrogen pentoxide is N2O5 • phosphorus tribromide is PBr3 • The prefix represents the subscript.  If the subscript is one mono is not needed.

  12. Binary Molecules Name these ::: Use Old Naming system and Stock system • PCl3 • PCl5 • SO2 Phosphorus TriChloride Phosphorus(III) Chloride Phosphorus PentaChloride Phosphorus(V) Chloride Sulfur Dioxide Sulfer (IV) Oxide

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