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Chemical Formulas & Chemical Compounds

Chemical Formulas & Chemical Compounds. NOMENCLATURE. Can you remember the name of every student in your class? Your School?. But… can you name all of the inorganic compounds that are made from the over 100 elements in the periodic table?

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Chemical Formulas & Chemical Compounds

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  1. Chemical Formulas&Chemical Compounds NOMENCLATURE

  2. Can you remember the name of every student in your class? Your School? • But… can you name all of the inorganic compounds that are made from the over 100 elements in the periodic table? • (That means combinations of 2 or more elements, atoms, or ions!) • Or about a gazillion combinations!!!

  3. Fortunately, you do not need to memorize the names of the compounds. All you need to do is know the names of the elements and ions (and you’ve already done that!)

  4. And all we need is a pattern or set of rules to govern the nomenclature of inorganic compounds. The following rules will guide you through the nomenclature of inorganic compounds.

  5. BINARY COMPOUNDS OF METALS WITH FIXED CHARGES Given Formula, Write the Name A binary compound is one made of two different elements. Examples NaCl KF Na2O AlBr3

  6. REMEMBER!All elements/ions involved have only one charge. That includes both theCation (positive, or metallic ion)and Anion (negative, or nonmetallic ion)

  7. THE “CATION” • The cation always comes first in the formula and the name. • Use the name of the cation with a fixed charge directly from the periodic table.

  8. THE “ANION” • The anion always comes second in both the formula and the name. • The name of the anion will be made from the root of the element’s name plus the suffix “-ide”. • Chlorine = chloride ion • Fluorine = fluoride ion • Bromine = bromide ion • Iodine = iodide ion

  9. Unusual Anions • Some anions don’t exactly follow the rules. • Sulfur: Sulfide ion (not sulfuride) • Oxygen: Oxide ion (not oxygenide) • Phosphorus: Phosphide ion (not phosphoride) • Nitrogen: Nitride (not nitrogenide)

  10. No polyatomic ions yet!! No variable charge anions yet!!

  11. Example: H2S • Step #1: Look at the first element (cation) and name it. • HYDROGEN • Step #2: Look at the second element. Use the root of its full name and change the ending to “ide”. • SULFIDE • (Notice that the presence of the subscript is ignored) • Name: HYDROGEN SULFIDE

  12. Example: NaCl • Step #1: Look at the first element (cation) and name it. • SODIUM • Step #2: Look at the second element. Use the root of its full name and change the ending to “ide”. • CHLORIDE • Name: SODIUM CHLORIDE

  13. Example: MgBr2 • Step #1: Look at the first element (cation) and name it. • MAGNESIUM • Step #2: Look at the second element. Use the root of its full name and change the ending to “ide”. • BROMIDE • (Notice that the presence of the subscript is ignored) • Name: MAGNESIUM BROMIDE

  14. Here’s some more practice • MgS • Magnesium sulfide • Ba3N2 • Barium nitride • CaO • Calcium oxide • BeBr2 • Beryllium bromide

  15. BINARY COMPOUNDS OF METALS WITH FIXED CHARGES Given Name, Write the Formula

  16. A few points to remember… • The order for names in a binary compound is FIRST THE CATION, THEN THE ANION. • (+) then (-) • Metal then nonmetal

  17. Group 1 = +1 Group 2 = +2 Group 12 = +3 Group 17 = -1 Group 16 = -2 Group 15 = -2 Remember your ion charges. (oxidation numbers) You were asked to memorize the formulas and oxidation number (charges) of these ions!Use your periodic table!!!

  18. Use your Algebraic skills! • The sum of the positive charges and the sum of the negative charges MUST add up to zero. • You may NOT adjust the charges of the cations or anions to get a total charge of zero. • You MAY adjust the subscripts to get a total charge of zero.

  19. Two methods may be used to write the formulas for these types of compounds. • Charge Crossing Technique (or “criss-cross” method). • Least Common Multiple Technique.

  20. THE CHARGE CROSSING TECHNIQUE • Rules are: • The total positive charges must equal the total negative charges. • You cannot change the charges given to you. • Adjust the subscripts to equalize the charges.

  21. Example #1: Sodium Chloride Step #1: Write down the two ions next to each other in the proper order. Na+1 Cl-1 Step #2: Move the positive charge (dropping the “sign”) to the subscript of the anion. Na+1 Cl-1 Step #3: Move the negative charge (dropping the “sign”) to the subscript of the cation. Na+1 Cl-1

  22. Step #4: The result of all this moving is… Na1Cl1 Step #5: Since subscripts of “one” are never written, but understood to be present, the final answer is: NaCl

  23. Example #2: Magnesium Bromide Step #1: Write down the two ions next to each other in the proper order. Mg+2 Br-1 Step #2: Move the positive charge (dropping the “sign”) to the subscript of the anion. Mg+2 Br-1 Step #3: Move the negative charge (dropping the “sign”) to the subscript of the cation. Mg+2 Br-1

  24. Step #4: The result of all this moving is… Mg1Br2 Step #5: Since subscripts of “one” are never written, but understood to be present, the final answer is: MgBr2

  25. Example #3: Aluminum Oxide Step #1: Write down the two ions next to each other in the proper order. Al+3 O-2 Step #2: Move the positive charge (dropping the “sign”) to the subscript of the anion. Al+3 O-2 Step #3: Move the negative charge (dropping the “sign”) to the subscript of the cation. Al+3 O-2

  26. Step #4: The result of all this moving is… Al2O3 Step #5: The final answer is: MgBr2

  27. Example #4: Barium Oxide Step #1: Write down the two ions next to each other in the proper order. Ba+2 O-2 Step #2: Move the positive charge (dropping the “sign”) to the subscript of the anion. Ba+2 O-2 Step #3: Move the negative charge (dropping the “sign”) to the subscript of the cation. Ba+2 O-2

  28. Step #4: The result of all this moving is… Ba2O2 Step #5: Since both subscripts have a common factor of “2”, we are not at a minimum set of subscripts. After reducing, the final answer is: BaO

  29. Least Common Multiple Technique The rules to follow (again) are: The total positive charges must equal the total negative charges. You cannot change the charges given to you. Adjust the subscripts to equalize the charges.

  30. Example #1: Aluminum Sulfide Step #1: Write down the two ions next to each other and in the proper order. (Cation first, then anion) Al+3S-2 Step #2: Select the least common multiple between the two charges (ignoring the signs!). In this case it is “6”. This is the amount of positive charge and negative charge you need for a correct formula. In other words, you need sufficient aluminum ions to make a +6 charge and sufficient sulfide ions to make a -6 charge.

  31. Step #3: Obviously, (I hope), you see that you need two aluminum ions and three sulfide ions to accomplish these numbers. Show this in the formula by using subscripts for each symbol. Remember… the subscripts go AFTER the symbols they represent! Al2S3

  32. Example #2: Radium Oxide Step #1: Write down the two ions next to each other and in the proper order. (Cation first, then anion) Ra+2O-2 Step #2: Select the least common multiple between the two charges (ignoring the signs!). In this case it is “2”. This is the amount of positive charge and negative charge you need for a correct formula. In other words, you need sufficient aluminum ions to make a +2 charge and sufficient sulfide ions to make a -2 charge.

  33. Step #3: Obviously, (I hope), you see that you need one radium ion and one oxide ion to accomplish these numbers. Show this in the formula by using subscripts for each symbol. Remember… we never write a subscript of one! RaO

  34. Binary Compounds of Cations with Variable ChargesGiven Formula, Write the Name • Remember… the CATION is the positively charged ion. It is the one that comes first in the name and formula. • These cations have AT LEAST TWO CHARGES. • The anions involved in these formulas have ONE possible charge.

  35. The variable charge cations you will be responsible for are: • SymbolStock System NameCommon Name Cu+ copper (I) cuprous Cu+2 copper (II) cupric Fe+2 iron (II) ferrous Fe+3 iron (III) ferric Sn+2 tin (II) stannous Sn+3 tin (III) stannic Cr+2 chromium (II) chromous Cr+3 chromium (III) chromic Mn+2 manganese (II) manganous Mn+3 manganese (III) manganic

  36. The variable charge cations you will be responsible for are: • SymbolStock System NameCommon Name Hg2+2 mercury (I) mercurous Hg+2 mercury (II) mercuric Pb+2 lead (II) plumbous Pb+3 lead (III) plumbic Co+2 cobalt (II) cobaltous Co+3 cobalt (III) cobaltic Au+ gold (I) aurous Au+3 gold (III) auric Some others may pop up during the course of this year. Pay attention in class and add them to this list!

  37. Example #1: FeCl2 Stock System Step #1: The first part of the name is the unchanged name of the first element in the formula. This is always the cation (metal) Iron

  38. Step #2: The result from step one WILL be followed by a Roman numeral. But what Roman numeral?? To find this out, multiply the charge of the anion (the Cl) by its subscript. Ignore the fact that it is negative. In this example: 1x2 = 2 Divide this result by the subscript of the cation (the Fe). (2/1 = 2) This the value of the Roman numeral to use. II

  39. Step #3: Since the result of Step #2 is “II”, we then use iron (II) for the cation in the name of this compound. Iron (II) Step #4: Write the complete correct name for the compound. The cation is written first follwed by the anion using the “ide” ending rule. Iron (II) chloride

  40. The Common Name System The charge on the cation is found in the same way as the stock system. For FeCl2, it is the Fe+2 cation. Instead of using iron (II) as the name of the cation, the common name is used: Fe+2 = ferrous FeCl2 = ferrous chloride

  41. Example #2: CuCl2 The first part of the name comes from the first element symbol: Copper The Roman numeral is II because 2 chloride ions equal a -2 charge. Copper (II) So the Cu must be +2 because the total (net) charge on the compound must equal zero.

  42. The second part of the name comes from the root of the second symbol plus “ide”. Chloride The correct name of the compound: CuCl2 = copper (II) chloride

  43. Using the “Common Name System”… Cu+2 = cupric ion So CuCl2 = cupric chloride

  44. Binary Compounds of Cations with Variable ChargesGiven Name, Write the Formula • Example #1: Iron (III) Sulfide Step #1: The first word tells you the symbol of the cation Fe Step #2: The Roman numeral will tell you the charge on the cation. In this case: Fe+3

  45. Step #3: The anion symbol and charge comes from the second name. In this case, sulfide means: S-2 Step #4: Since you know the symbols and their charges, form this point, you can either use the “criss-cross” method or “least common multiple” method to write the formula. Iron (III) sulfide = Fe2S3

  46. Binary Compounds of Two NonmetalsGiven Formula, Write the Name • These types of compounds are commonly called “molecular compounds”. • All other types that we’ve discussed so far are commonly called “ionic compounds”. • IMPORTANT: No metals (which act as the cation) are involved!!!! • That means one of the nonmetals will be acting in the positive role while the other is negative.

  47. In fact… you do not even know the charges! • The formula comes right from the element names and their prefixes. • Nothing to look up! • No decisions to make! • Except… • You must memorize the Greek prefixes that are used.

  48. One (1) = mono- Two (2) = di- Three (3) = tri- Four (4) = tetra- Five (5) = penta- Six (6) = hexa- Seven (7) = hepta- Eight (8) = octa- Nine (9) = nona- Ten (10) = deca- Greek Number Prefixes to Memorize

  49. These are some of the easiest compounds to name. • BUT… First-year Chemistry students often want to use this method for naming ALL compounds. THIS METHOD IS ONLY FOR COMPOUNDS MADE FROM TWO NONMETALS!!!!!

  50. Examples • N2O, NO2, N2O3, N2O5, NO, NO3… • See how confusing this could get??? • Not if we use prefixes that tell us how many of each element is present. • For instance: • In N2O we have two nitrogen atoms and one oxygen atom. • So… dinitrogenmonoxide • I know… we drop the second “o” in mono so the name doesn’t sound weird.

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