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Chapter 7

Chapter 7. Chemical Formulas and Chemical Compounds. 7-1 Chemical Names & Formulas. Explain the significance of a chemical formula. Determine the formula for an ionic compound formed between two given ions. Name an ionic compound given its formula.

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Chapter 7

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  1. Chapter 7 Chemical Formulas and Chemical Compounds

  2. 7-1 Chemical Names & Formulas • Explain the significance of a chemical formula. • Determine the formula for an ionic compound formed between two given ions. • Name an ionic compound given its formula. • Using prefixes, name a binary molecular compound. • Write the formula of a binary molecular compound.

  3. Significance of a Chemical Formula Molecular formulas Number of atoms of each element in one molecule of a compound C2H6 = ethane (2 carbon atoms, 6 hydrogen atoms)

  4. Significance of a Chemical Formula Ionic Compounds Represents the simplest whole number ratio of the compounds cations and anions Al2(SO4)3 = aluminum sulfate (2 aluminum ions, 3 sulfate ions)

  5. Monatomic Ions • Ions formed from a single atom

  6. Naming Monatomic Ions • Monatomic cations are identified by the elements name. • Monatomic anions: Drop the ending of the element. Add an “-ide” ending.

  7. Binary Ionic Compounds • Binary compounds-are compounds composed of two different elements.

  8. Binary Ionic Compounds Writing Formulas for Binary Ionic Compounds • Write the symbols of the ions side by side. ALWAYS write the cation first. • Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion. • Check that the subscripts are in whole numbers.

  9. Writing Formulas for Binary Ionic Compounds • Write the symbols of the ions side by side. ALWAYS write the cation first. Example: Silver sulfide Ag+S2-

  10. Writing Formulas for Binary Ionic Compounds • Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion. Example: Ag2+S12-

  11. Writing Formulas for Binary Ionic Compounds • Check that the subscripts are in the smallest whole numbers they can. Example: Ag2S

  12. Binary Ionic Compounds Naming Binary Ionic Compounds from their Formulas • Name the cation • Name the anion

  13. Naming Binary Ionic Compounds from their Formulas Example: Al2S3 • Name the cation: aluminum • Name the anion: sulfide aluminum sulfide

  14. Stock System of Nomenclature • Roman numerals are used to denote the charge of metals can form two or more cations. • The number is enclosed in parentheses and placed immediately after the name. • Roman numerals are never used for anions or metals that form only one ion.

  15. Compounds Containing Polyatomic Ions • Oxyanions-polyatomic anions that contain oxygen.

  16. Naming a series of Polyatomic Ions

  17. Naming Compounds with Polyatomic Ions Example: PClO3 • Name the cation: phosphorous • Name the polyatomic ion: chlorate phosphorous chlorate

  18. Writing Formulas with Polyatomic Ions • Use parentheses when you need more than one polyatomic ion. • Parentheses are never used for monatomic ions no matter how many are in the formula.

  19. Binary Molecular Compounds • Covalently bonded molecules containing only two elements, both nonmetals. • The first element gets a prefix if there is more than one of that element. • Second element always gets a prefix and an “-ide” ending.

  20. Binary Molecular Compounds Examples: N2O3 = dinitrogen trioxide CO = carbon monoxide, not monocarbon monoxide

  21. Binary Molecular Compounds Examples: N2O9 = dinitrogen nonoxide CO6 = carbon hexoxide, not monocarbon hexoxide

  22. Acids & Salts • Binary Acids-acids that consist of two elements, usually hydrogen and one of the halogens. • Oxyacids-acids that contain hydrogen, oxygen and a third element (usually a nonmetal).

  23. 7-2 Oxidation Numbers • List the rules for assigning oxidation numbers. • Give the oxidation number for each element in the formula of a chemical compound. • Name the binary molecular compounds using oxidation numbers and the stock system.

  24. Oxidation number • Numbers assigned to atoms composing a compound or ion that indicate the general distribution of electrons among bonded atoms.

  25. Assigning Oxidation Numbers • The atoms of a pure element have an oxidation number of zero. Example: 00 Au F2

  26. Assigning Oxidation Numbers • The first element in a binary compound is assigned the number equal to the charge it would have as an anion. The second element is assigned the number equal to the charge it would have as a cation. Example: +5-2 As2 S5

  27. Assigning Oxidation Numbers • Fluorine has an oxidation number of -1 in all of its compounds. Example: +4-1 C F4

  28. Assigning Oxidation Numbers • Oxygen has an oxidation number of -2 in almost all of its compounds. It is a -1 in peroxides, and a +2 in compounds with fluorine.

  29. Assigning Oxidation Numbers • Hydrogen has an oxidation number of +1 in all compounds containing elements that are more electronegative than it; it has an oxidation number of -1 in compounds with metals.

  30. Assigning Oxidation Numbers • The algebraic sum of the oxidation numbers of all atoms in a neutral compound is equal to zero.

  31. Assigning Oxidation Numbers • The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to its charge.

  32. Assigning Oxidation Numbers • For monatomic ions, the oxidation number is equal to the charge.

  33. Using Oxidation Numbers • Be aware that the stock number (Roman Numerals) system may be used for molecular compounds as well as ionic compounds.

  34. 7-3 • Calculate the formula mass or molar mass of any given compound. • Use molar mass to convert between mass and moles. • Calculate the number of molecules, formula units, or ions in a given molar amount of a chemical compound. • Calculate the percentage composition of a chemical compound.

  35. Formula Mass • Formula Mass-the sum of the average atomic masses of all the atoms represented in the formula of a molecule, formula unit, or ion

  36. Formula Mass • Calculate the formula mass of magnesium carbonate, MgCO3. 24.31 + 12.01 + 3(16.00) = 84.32 amu

  37. Molar Mass • A compound's molar mass is numerically equal to it formula mass, but expressed in units of grams/mole (g/mol).

  38. Molar Mass • Calculate the Molar mass of magnesium carbonate, MgCO3. 24.31 g/mol+12.01g/mol+3(16.00 g/mol) = 84.32 g/mol

  39. Molar Mass as a Conversion Factor • Converting moles of compound to grams

  40. Molar Mass as a Conversion Factor • Converting grams of compound to moles

  41. Calculating Percentage Composition • Calculate the percentage composition of magnesium carbonate, MgCO3. 24.31 g + 12.01 g + 3(16.00 g) = 84.32 g

  42. Calculating Percentage Composition • Calculate the percentage composition of magnesium carbonate, MgCO3. 24.31 g + 12.01 g + 3(16.00 g) = 84.32 g

  43. Calculating Percentage Composition • Calculate the percentage composition of magnesium carbonate, MgCO3. 24.31 g + 12.01 g + 3(16.00 g) = 84.32 g

  44. Hydrates • Crystalline compounds in which water molecules are bound in the crystal structure Copper (II) sulfate pentahydrate CuSO4 • 5H20 The raised dot means "Water is loosely attached" It does NOT mean multiply when determining formula weight

  45. 7-4 • Define empirical formula, and explain how the term 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.

  46. Formulas • Empirical Formula - the lowest whole number ration of atoms in a compound.

  47. Formulas • Molecular Formula-the true number of atoms of each element in the formula of a compound.

  48. Formulas • Formulas for ionic compounds are ALWAYS empirical.

  49. Formulas Molecular: H2O Empirical: H2O

  50. Formulas Molecular: C6H12O6 CH2O Empirical:

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