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Nomenclature & Formulas

Nomenclature & Formulas. Types of Formulas. The formulas for compounds can be expressed as an empirical formula and as a molecular(true) formula. Empirical Molecular (true ) Name CH C 2 H 2 acetylene CH C 6 H 6 benzene CO 2 CO 2 carbon dioxide

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Nomenclature & Formulas

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  1. Nomenclature & Formulas

  2. Types of Formulas The formulas for compounds can be expressed as an empirical formula and as a molecular(true) formula. Empirical Molecular (true) Name CH C2H2 acetylene CH C6H6 benzene CO2CO2 carbon dioxide CH2O C5H10O5 ribose

  3. An empirical formula represents the simplest whole number ratio of the atoms in a compound. • The molecular formula is the true or actual ratio of the atoms in a compound.

  4. Formulas… • Structural Formulas tell us- • Shows the way the atoms are joined together in a molecule. • Chemical Formulas tell us- • Elements that make up the compound • Ratio of the elements in the compound • Subscripts –below the element • Tell you the number of atoms Example- Example- Water-> H2O-> 2 hydrogen atoms and one oxygen atom • Carbon always forms 4 bonds • Molecular Models show orientation in 3 dimensions so are the best molecular models • Molecular Formulas tell us- • Tell you the total number of atoms of each element in 1 molecule of the substance Example- C2H2 ->Acetylene

  5. Empirical and Molecular Formulas molar mass = a whole number = n simplest mass n = 1 molar mass = empirical mass molecular formula = empirical formula n = 2 molar mass = 2 x empirical mass molecular formula = 2 x empirical formula molecular formula = or > empirical formula

  6. Molecular Formula Empirical Formula Molecular Mass Empirical Mass Timberlake LecturePLUS

  7. The Empirical Formula • The lowest whole number ratio of elements in a compound. • The molecular formula the actual ratio of elements in a compound • The two can be the same. • CH2 empirical formula • C2H4 molecular formula • C3H6 molecular formula • H2O both

  8. Calculating Empirical • Just find the lowest whole number ratio • C6H12O6 • CH4N • It is not just the ratio of atoms, it is also the ratio of moles of atoms • In 1 mole of CO2there is 1 mole of carbon and 2 moles of oxygen • In one molecule of CO2 there is 1 atom of C and 2 atoms of O

  9. Calculating Empirical • Pretend that you have a 100 gram sample of the compound. • That is, change the % to grams. • Convert the grams to mols for each element. • Write the number of mols as a subscript in a chemical formula. • Divide each number by the least number. • Multiply the result to get rid of any fractions.

  10. Example • Calculate the empirical formula of a compound composed of 38.67 % C, 16.22 % H, and 45.11 %N. • Assume 100 g so • 38.67 g C x 1mol C = 3.220 mole C 12.01 gC • 16.22 g H x 1mol H = 16.09 mole H 1.01 gH • 45.11 g N x 1mol N = 3.219 mole N 14.01 gN

  11. 3.220 mol C and 3.219 mol N are essentially the same. • 3.220 mole C • 16.09 mole H • 3.219 mole N C3.22H16.09N3.219 If we divide all of these by the smallest one, it will give us the empirical formula

  12. Example • The ratio is 3.220 mol C = 1 mol C 3.219 molN 1 mol N • The ratio is 16.09 mol H = 5 mol H 3.219 molN 1 mol N • C1H5N1 is the empirical formula = CH5N • A compound is 43.64 % P and 56.36 % O. What is the empirical formula?

  13. 43.6 g P x 1mol P = 1.4 mole P 30.97 gP • 56.36 g O x 1mol O = 3.5 mole O 16 gO P1.4O3.5

  14. Divide both by the lowest one • The ratio is 3.52 mol O = 2.5 mol O 1.42 mol P 1 mol P P1.4O3.5 This doesn’t work! P1O2.5

  15. Multiply the result by 2 to get rid of any fractions. P1O2.5 = P2O5 2 X

  16. Solve • Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

  17. Empirical to Molecular • Since the empirical formula is the lowest ratio the actual molecule would weigh more by a whole number multiple. • Divide the actual molar mass by the mass of one mole of the empirical formula.

  18. Caffeine has a molar mass of 194 g. what is its molecular formula? (You found Caffeine’s empirical formula earlier, solve for the empirical formula mass.) Find x if 194 g 97 g = 2 C4H5N2O1 2 X C8H10N4O2.

  19. Example • A compound is known to be composed of 71.65 % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) is known to be 98.96 g. What is its molecular formula?

  20. Example 71.65g Cl 24.27g C 4.07g H = 2.0mol = 2.0mol = 4.0mol

  21. We divide by lowest (2mol ) would give an empirical massof 48.5g/mol • Cl1C1H2 Cl2C2H4 Its molar mass is known (from gas density) is known to be 98.96 g. What is its molecular formula? = 2 = Cl2C2H4 2 X Cl1C1H2

  22. Chemical Names & Formulas: Ionic Compounds

  23. What's in a Name? Kaylee Braxton Cole Samantha Rachel Lauren Alex Rebekah David Evan Jessie Amanda Dani Alexis Michelle Mackenzie Brendan Victoria Maegan Becky Susanna Naming Chemicals Brian Chelsea

  24. Chemical Formulas Humpty Dumpty’s Downfall Eggshells are made of mostly ionic compounds such as calcium phosphate, Ca3(PO4)2, which makes them brittle. When broken, eggshells break into many pieces that can’t be put back together again.

  25. Binary Ionic Compounds Formulas are the language used to give information about chemicals. As a first step in studying this new language, you will learn how to name and write formulas for ionic compounds. Sodium chloride (NaCl) contains only sodium and chlorine. Potassium iodide (KI) contains only potassium and iodine. Each is an example of a binary compound, which is a compound that contains only two elements.

  26. Binary ionic compounds can have more than one ion of each element, as in CaF2, but they are not composed of three or more different elements.

  27. To name binary compounds,: First, write the name of the positively (+) charged ion, usually a metal. Second, add the name of the nonmetal or negatively (-) charged ion. Third, change the end of the name to -ide. For example: NaCl (+) is Na; (-) is Cl 1st: Na = Sodium 2nd: Cl = Chlorine Write: Sodium Chlorine Change: -ine to -ide  Chloride Put them together: Sodium Chloride

  28. Naming cations Naming anions Some oddballs: Nitrogen --> Nitride Sulfur --> Sulfide

  29. Try some: AlCl3 ________________ ___________________ ZnI2 ________________ ___________________ CaF2 ________________ ___________________ CaO ________________ ___________________ Al2O3 ________________ ___________________ Al2O3 CaO CaF2

  30. Sodium chloride contains sodium ions that have a +1 charge and chloride ions that have a -1 charge. You have learned that compounds are electrically neutral. This means that the sum of the charges in an ionic compound must always be zero. One Na+ balances one Cl- in sodium chloride. When you write a formula, you add subscripts to the symbols for the ions until the algebraic sum of the ions’ charges is zero. Example: Ca + F  [Ca]2+ + F- + F -  [Ca]2+ + 2F-  CaF2 Remember, the +’s and the -’s must cancel each other out.

  31. If you have more than one ion of a given element in a compound, the subscript indicates how many ions are present. The subscript is predicted by the charges on the atoms. Alumina is the common name for aluminum oxide. Aluminum is in group 3, so it has 5 electrons and will lose 3 to become Al3+. Oxygen has 6 valence electrons, so it will gain 2 electrons to become O2-. Al + O  Al3+ + O 2-

  32. Notice that one of aluminum’s 3 electrons has not been taken up by oxygen. Because all the electrons must be accounted for, more than one oxygen atom must be involved in the reaction. But oxygen cannot going only one electron, so a second aluminum atom must be added to give a second electron to oxygen. In all, two Al3+ ions must bond with three O2- ions to form Al2O3. Remember that the charges in the formula for aluminum oxide must add up to zero. 2Al3+ + 3O2-  Al2O3 Al + Al + O + O + O  Al3+ + Al3+ + O 2- + O 2- + O 2-

  33. The easy way!

  34. Writing a Simple Formula Write the formula for an ionic compound containing sodium and sulfur. Analyze: Sodium is in Group 1, so it has an oxidation number of +1. Sulfur is in group 6, so it has an oxidation number of -2. Set up: Write the symbols for sodium and sulfur ions in formula form, placing the positive ion first:Na+S2- Solve: The formula as written has one positive charge and two negative charges. To keep neutrality, one more positive charge is needed to balance the 2- charge. This is done by adding a second sodium to the formula. The correct formula is then written as Na2S. Check: Check to be sure that you have not changed the charges of the ions and that the overall charge of the formula is zero. 2(+1) + (-2) = 0 The formula is written correctly.

  35. Try these: Write the formula for each of the following compounds: Lithium oxide Calcium bromide Sodium oxide Aluminum sulfide

  36. Try these: Write the formula for the compound formed from each of the following pairs of elements: • Barium and oxygen • Strontium and iodine • Lithium and chlorine • Radium and chlorine

  37. Some ions contain more than one element. These are called polyatomic ions. In a polyatomic ion, a group of atoms is covalently bonded. Although the individual atoms have no charge, the group as a whole has a charge. The formulas and names of some common polyatomic ions are shown. Although the charge is shown to the right of the formula, it is the whole ion, rather than the last atom listed, that is charged.

  38. To name a compound containing a polyatomic ion, follow the same rules as used in naming binary compounds. Name the positive ion first, followed by the negative ion. However, do not change the ending of the negative polyatomic ion. Example: Calcium Carbonate (Ca2+CO32-), found in TUMS.

  39. Try these: Na2CrO4 _________________ __________________ KOH _________________ __________________ Mg(NO3) _________________ __________________ Ca(C2H3O2) _________________ __________________ (NH4)2SO4 _________________ __________________ NH4Br _________________ __________________

  40. Write the formula for the compound that contains lithium and carbonate ions. Analyze: Lithium is in group 1, so it has a +1 charge. According to the table on the previous slides, the carbonate ion has a -2 charge, and its structure is CO32-. Set up: Write the symbols for lithium carbonate in formula form: Li+ CO32- Solve: Decide the correct ratio of lithium ions to carbonate ions by looking at their charges. In this case, the sum of the positive and negative charges does not equal zero. Two lithium ions are needed to balance the carbonate ion. Because you cannot change the charges of the ions, you must ass a subscript of 2 to the Li+. The correct formula for lithium carbonate is Li2CO3. Check: Check to be sure the overall charge is zero: 2(1) + (-2) = 0 The formula is correct.

  41. Writing the formulas for polyatomic ionic compounds is the same as for binary ionic compounds. Remember, if there is more than one polyatomic ion, use parentheses () around it. If there is only one, no need for ().

  42. Try these: 1. A compound containing ammonium and sulfite ions. 2. A compound containing barium and nitrate ions. NH4+ SO32- x2 x2 +1 -2 (NH4)2SO3 Ba NO3- x2 x2 +2 -1 Ba(NO3)2

  43. 3. A compound containing calcium and phosphate ions. 4. Write the formula for sodium phosphate. 5. Write the formula for magnesium hydroxide.

  44. 6. Write the formula for potassium dichromate. 7. Write the formula for aluminum sulfate.

  45. Chemical Names & Formulas Transition Compounds

  46. Naming Transition Compounds Transition elements form positive ions, just like other metals, but most transition elements can form more than one type of positive ion. In other words, transition elements can have more than one oxidation number. Copper (II) sulfate on the left forms a blue crystal. The oxidation number is +2. Copper (I) sulfate on the right forms a black crystal. The oxidation number is +1.

  47. Naming transition compounds is very easy. Follow the same rules you learned for binary and polyatomic ions. Add in the oxidation number between the 2 names in the form of Roman numerals. CrO Cr2O3 CrO3

  48. Try these: Write the names of the following compounds: Pb(NO3)2 ____________________________________________ Mn2O3 ____________________________________________ Ni(C2H3O2)2 ____________________________________________ HgF2 ____________________________________________ CuBr3 _____________________________ Co3P2 _____________________________ AuI _____________________________ WAt2 _____________________________ Pt2Ac3 _____________________________

  49. Writing the formula for transition compounds: Follow the same rules as you did for writing binary or polyatomic ionic compound formulas. The only difference is that you have to pay attention to the oxidation number. Try these: Copper (I) and sulfite Tin (IV) and fluoride Gold (III) and cyanide Lead (II) and sulfide.

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