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Chemical formulas and compounds


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Chemical formulas and compounds

  1. 1. Chapter 7
  2. 2. <ul><li>Significance of A Chemical Formula </li></ul><ul><ul><li>Indicates the relative number of atoms of each kind in a chemical compound </li></ul></ul><ul><ul><li>Reveals the number of atoms of each element contained in a single molecule </li></ul></ul><ul><ul><li>Example: C 8 H 18 </li></ul></ul><ul><ul><li> ↑ ↑ </li></ul></ul><ul><ul><li>The subscripts indicate the number of atoms in a molecule of octane </li></ul></ul><ul><ul><li> </li></ul></ul>Chemical Names and Formulas
  3. 3. <ul><li>Monatomic ions – ions formed from a single atom. </li></ul><ul><li>In naming anions, drop the elements ending and add “ide”. </li></ul><ul><li>Ex. Oxygen to Oxide </li></ul>Monatomic Ions
  4. 4. <ul><li>Binary compounds – compounds composed of two different elements. </li></ul>Binary Ionic Compounds Na + + Cl - NaCl Ca 2+ + F - CaF 2 Ca 2+ + N 3- Ca 3 N 2
  5. 5. <ul><li>Nomenclature – the naming system of binary ionic compounds involves combining the names of the compound’s positive and negative ions. </li></ul>Naming Binary Ionic Compounds Al 2 O 3 Name of cation Name of anion aluminum oxide
  6. 6. The Stock System of Nomenclature CuCl 2 Name of cation + Roman numeral indicating charge Name of anion copper(II) chloride Oxyanions – polyatomic ions containing oxygen.
  7. 7. Naming Binary Molecular Compounds Number Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-
  8. 8. P 4 O 10 Prefix needed if there is more than one atom + Name of less – electronegative element Prefix indicated by the number of atoms contributed by more-electronegative element Root name of more-electronegative element + ide + tetraphosphorus decoxide
  9. 9. <ul><li>Each atom is joined to all its neighbors in a covalently bonded, 3-D network. </li></ul><ul><li>The subscripts in a formula indicates the smallest whole-number ratio of the atoms in the compound. </li></ul>Covalent-Network Compounds
  10. 10. <ul><li>Acid – a molecular substance that when dissolved in water creates a solution with hydrogen ion activity. </li></ul><ul><li>Binary acids – acids consisting of two elements. </li></ul><ul><li>Oxyacids – acids containing hydrogen, oxygen, and a third element. </li></ul><ul><li>Salt – an ionic compound composed of a cation and the anion from an acid. </li></ul>Acids and Salts
  11. 11. <ul><li>The oxidation state of any element such as Fe, H 2 , O 2 , P 4 , S 8 is zero (0). </li></ul><ul><li>The more electronegative element is assigned an negative oxidation number of it’s charge. </li></ul><ul><li>The less electronegative element is assigned a positive oxidation number of it’s charge. </li></ul><ul><li>The oxidation state of oxygen in its compounds is -2, except for peroxides like H 2 O 2 , and Na 2 O 2 , in which the oxidation state for O is -1. When in a compound with halogens, such as OF 2 , the oxidation number for O is +2. </li></ul><ul><li>The oxidation state of hydrogen is +1 in its compounds, except for metal hydrides, such as NaH, LiH, etc., in which the oxidation state for H is -1. </li></ul>Oxidation Numbers
  12. 12. <ul><li>The oxidation states of other elements are then assigned to make the algebraic sum of the oxidation states zero. </li></ul><ul><li>The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion. </li></ul>HClO 3 -2 -6 +1 +1 +5 +5 H = +1, Cl = +5, O = -2
  13. 13. Using Oxidation Numbers for Formulas and Names The Stock System is based on oxidation numbers and can be used as an alternative way to the prefix system. Formula Prefix System Stock System PCl 3 phosphorus trichloride phosphorus (III) chloride PCl 5 phosphorus pentachloride phosphorus (V) chloride
  14. 14. Using Chemical Formulas Formula Masses Finding the formula mass for H 2 O Step 1: Find the average atomic mass for hydrogen and oxygen Step 2: Use the conversion table to change atoms to atomic mass units (amu) Average atomic mass of H: 1.01 amu Average atomic mass of O: 16.00 amu
  15. 15. 2 H atoms H atoms 1.01 amu = 2.02 amu 1 O atoms O atoms 16.00 amu = 16.00 amu Average mass of H 2 O molecule = 18.02 amu Step 3: Add the atomic mass units to find the average mass
  16. 16. Molar Mass Finding the molar mass for H 2 O Step 1: Find the molar mass for hydrogen and oxygen Step 2: Use the conversion table to change moles to grams. Molar mass of H: 1.01 g/mol Molar mass of O: 16.00 g/mol
  17. 17. 2 mol H 1 mol 1.01 g = 2.02 g 1 mol O 1 mol 16.00 g = 16.00 g Average mass of H 2 O molecule = 18.02 g Step 3: Add the masses to find the total mass