1. Chemical Formulas and Chemical Compounds Chapter 7

2. SC Standards C.3.2 – Interpret the names and formulas for ionic and covalent compounds C.4.4 – Apply the concept of moles to determine the number of particles of a substance in a chemical reaction, the percent composition of a representative compound, the mass proportions, and the mole mass relationship.

3. Objectives – Chemical Names and Formulas Explain the significance of a chemical formula. Write the formula of a binary molecular compound given its name. Name a molecular compound given its formula. Determine the formula of an ionic compound formed between two given ions. Name an ionic compound given its formula.

4. Chemical Names and Formulas Common names (such as salt, water, and limestone) usually give no information about chemical composition. A chemical formula indicates the relative number of atoms of each kind in a chemical compound.

5. Chemical Names and Formulas There are two types of chemical compounds – ionic and covalent (molecular). The type of compound is VERY, VERY, VERY important because it determines the way the compound is named.

6. Ionic Compounds Ionic Compounds are formed between:  a metal and a nonmetal  a metal and a polyatomic ion  a polyatomic ion and a nonmetal  two polyatomic ions A polyatomic ion is an ion made up of two or more atoms.

7. Covalent (Molecular) Compounds Covalent Compound are formed between two or more nonmetals. Nonmetals are located to the right side of the periodic table in the p block.  Group 17 and Group 18 are all nonmetals.  Some elements from Groups 13 – 16 are nonmetals.  Hydrogen is a nonmetal.

8. Significance of a Chemical Formula A chemical formula indicates the relative number of atoms of each kind in a chemical compound. For molecular (covalent) compounds:  The chemical formula (also called a molecular formula) indicates the number of atoms of each element contained in a single molecule of the compound.

9. Significance of a Chemical Formula For ionic compounds:  The chemical formula represents one formula unit – the simplest ratio of the compound’s positive ions (cations) and its negative ions (anions).

10. Naming Binary Molecular Compounds Naming binary (two element) molecular compounds involves the use of prefixes. NumberPrefix 1mono- 2di- 3tri- 4tetra- 5penta- 6hexa- 7hepta- 8octa- 9nona- 10deca-

11. Naming Binary Molecular Compounds In a molecular (covalent) compound, electrons are shared between the atoms that are bonded together. Only nonmetals are involved in forming binary molecular compounds. Positive and negative ions are NOT formed when binary molecular compounds form, instead, the available electrons are shared between atoms.

12. Naming Binary Molecular Compounds Rules for Using Prefixes to Name Binary (two element) Molecular Cmpds:  Name the first element. If there is more than one atom, add a prefix.  Name the second element. Add a prefix. Change the ending to –ide.  Drop the “o” or “a” at the end of the prefix if the word following it begins with a vowel.

13. Naming Binary Molecular Compounds Name the following:  As 2 O 5  SO 3  I Cl 3  PBr 5  HF  H 2 O  PI 3

14. Writing Formulas for Binary Molecular Cmpds Write the symbol for the first element. Indicate the number of atoms of that element using a subscript. Write the symbol for the second element. Indicate the number of atoms of the element using a subscript.

15. Writing Formulas for Binary Molecular Cmpds Write the molecular formula for the following compounds:  carbon tetraiodide  phosphorus trichloride  dinitrogen trioxide  carbon monoxide  diarsenic pentoxide

16. Naming Main Group Ionic Compounds Ionic Compounds are formed when positive and negative ions are held together by mutual attraction. In an ionic compound, one element (or group of elements) has a positive charge and the other element (or group of elements) has a negative charge.

17. Naming Main Group Ionic Compounds You DO NOT use prefixes when naming ionic compounds. Rules for Naming Main Group Ionic Cmpds:  Name the first element (or polyatomic ion).  Name the second element (or polyatomic ion) and change the ending to –ide if it is an element. (NOTE: do not change the ending if it is a polyatomic ion – leave it!)

18. Naming Main Group Ionic Compounds Name the following:  CaBr 2  CaCl 2  Al 2 O 3  KClO 3  NH 4 OH  NaCl  AlBr 3  SrI 2

19. Writing Formulas for Ionic Cmpds An element’s location on the periodic table can help you determine the charge on the ion that it will form. Group 1 = +1 (loses 1 valence electron) Group 2 = +2 (loses 2 valence electrons) Group 13 = +3 (loses 3 valence electrons)

20. Writing Formulas for Ionic Cmpds Group 14 = doesn’t typically form ions Group 15 = -3 (gains 3 electrons) Group 16 = -2 (gains 2 electrons) Group 17 = -1 (gains 1 electron) Group 18 = unreactive

21. Writing Formulas for Ionic Cmpds Writing formulas for ionic compounds is more complex than for a molecular formula. Determining the subscripts is more difficult because prefixes are not used with ionic compounds.

22. Writing Formulas for Ionic Cmpds Steps for writing formulas for ionic cmpds:  Write the symbols for the ions (including the charges) side by side. Write the cation (the positive ion) first.  Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion.  Check the subscripts and divide them by their largest common factor to give the smallest possible whole-number ratio of ions.

23. Writing Formulas for Ionic Cmpds In the name of a compound, the charge on a transition metal (and Sn or Pb) must be indicated by a Roman Numeral because most transition metals can form two or more cations w/ different charges. The exceptions to this are the following transition metals:  Ag +1, Zn +2, Cd +2 They do not need Roman Numerals.

24. Writing Formulas for Ionic Cmpds Write the chemical formula for the following compounds:  potassium iodide  magnesium chloride  sodium sulfide  copper (II) bromide  calcium nitrite  potassium perchlorate  iron (II) nitrate  iron (III) sulfide

25. Naming Ionic Cmpds with Transition Metals When ionic cmpds contain transition metals (and Sn or Pb), the charge on the transition metal must be determined before the formula can be written.

26. Naming Ionic Cmpds with Transition Metals To determine the charge on the transition metal (other than Ag, Zn, or Cd) you must “un-cross” the subscripts. Use the previous rules for writing the name making sure to add in a Roman Numeral to indicate the charge on the transition metal cation.

27. Naming Ionic Cmpds with Transition Metals Name the following compounds:  CoF 3  SnI 4  SnCl 2  FeS  Fe 2 (CrO 4 ) 3  Ag 2 O  CuO

28. Naming Acids and Salts An acid is a distinct type of molecular compound. The following are the names of some common acids that you need to know: HClhydrochloric acid H 2 SO 4 sulfuric acid HNO 3 nitric acid H 3 PO 4 phosphoric acid H 2 SO 3 sulfurous acid HNO 2 nitrous acid CH 3 COOHacetic acid

29. Objectives – Using Chemical Formulas Calculate the molar mass of any given compound. Use molar mass to covert between mass in grams and amount in moles of a chemical compound. Calculate the number of molecules, formula units, or ions in a given molar amount of a chemical compound. Calculate the percentage composition of a given chemical compound.

30. Molar Mass of a Compound The molar mass of a substance is equal to the mass in grams of one mole of a substance. The molar mass of a compound is calculated by adding the masses of all the elements present in a mole of the compound.

31. Molar Mass of a Compound Example – Determine the molar mass of water (H 2 O)  H x 2 = 1 g x 2 = 2 g  O x 1 = 16 g x 1 = 16 g  2 g H + 16 g O = 18 g The molar mass of water is 18 g/mol.

32. Molar Mass of a Compound Determine the molar mass of the following compounds:  Al 2 S 3  NaNO 3  Ba(OH) 2  Ba(NO 3 ) 2

33. Molar Mass as a Conversion Factor The molar mass of a compound can be used as a conversion factor, just like the molar mass of an element. It relates amount in moles to a mass in grams for the substance which you have determined the molar mass.

34. Molar Mass as a Conversion Factor Example: What is the mass in grams of 2.50 mol of oxygen gas (O 2 )?

35. Molar Mass as a Conversion Factor Example: Ibuprofen, C 13 H 18 O 2, is the active ingredient in many nonprescription pain relievers.  a) Determine its molar mass.  b) If the tablets in the bottle contain a total of 33 g of ibuprofen, how many moles of ibuprofen are in the bottle?  c) What is the total mass in grams of the carbon in 33 g of ibuprofen?

36. Percent Composition The percentage by mass of each element in a compound is known as the percentage composition of the compound. mass of element in one mole x 100 % molar mass of compound

37. Percent Composition Example – Find the percentage composition of copper (I) sulfide, Cu 2 S

38. Percentage Composition Example – As some salt crystallize from a water solution, they bind water molecules in their crystal structure. Sodium carbonate forms such a hydrate, in which 10 water molecules are present for every formula unit of sodium carbonate. Find the mass percentage of water in sodium carbonate decahydrate, Na 2 CO 3 10H 2 O.

39. Objectives – Determining Chemical Formulas Define empirical formula, and explain how the terms applies to ionic and molecular compounds. Determine an empirical formula from either a percentage or a mass composition. Explain the relationship between the empirical formula and the molecular formula of a given compound. Determine a molecular formula from an empirical formula.

40. Determining Chemical Formulas An empirical formula consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole-number mole ratio of the different atoms in the compound. For ionic compounds, the formula unit is usually the same as the compound’s empirical formula.

41. Determining Chemical Formulas For molecular compounds, the empirical formula does not necessarily represent the actual numbers of atoms present in each molecule.

42. Calculation of Empirical Formulas If you are given the % composition of a substance. Do the following to calculate the empirical formula:  #1) Assume you have a 100 g sample. Then, the % of each element will equal the number of grams you have.  #2) Convert the mass of each element into moles (using each element’s molar mass).  #3) Divide each number of moles by the smallest number of moles from step #2.  #4) If its not a whole # ratio after step #3, multiply each # by the smallest number you can think of that will produce a whole # ratio.

43. Calculation of Empirical Formulas Example – Quantitative analysis shows that a compound contains 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. Find the empirical formula of this compound.

44. Calculation of Empirical Formulas Example – Analysis of a 10.150 g sample of a compound know to contain only phosphorus and oxygen indicates a phosphorus content of 4.433 g. What is the empirical formula of this compound?

45. Calculation of Molecular Formulas A molecular formula is the actual formula of a molecular compound. It is either equal to the empirical formula or is a multiple of it. The relationship b/w the two is shown below: x(empirical formula) = molecular formula

46. Calculation of Molecular Formulas To calculate the molecular formula from the empirical formula, you must have the molar mass of each. Divide the molecular formula’s molar mass by the empirical formula’s molar mass. The number you get should be a whole number. Each subscript in the empirical formula must be multiplied by this number to give you the molecular formula.

47. Calculation of Molecular Formulas Example – The empirical formula of a compound is P 2 O 5. Experimentation shows that the molar mass of this compound is 283.89 g/mol. What is the compound’s molecular formula?