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Chemistry Chapter 6

Chemistry Chapter 6. Chemical Names and Formulas. Section 6.1 Introduction to Chemical Bonding. Objectives: Distinguish between ionic and molecular compounds Define cation and anion and relate them to metal and nonmetal. Molecules and Molecular Compounds.

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Chemistry Chapter 6

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  1. Chemistry Chapter 6 Chemical Names and Formulas

  2. Section 6.1 Introduction to Chemical Bonding • Objectives: • Distinguish between ionic and molecular compounds • Define cation and anion and relate them to metal and nonmetal

  3. Molecules and Molecular Compounds • Monatomic – atoms that exist as isolated atoms. (i.e. most noble gases) • A moleculeis the smallest electrically neutral unit of a substance that still has the properties of the substance. Molecules are made up of two or more atoms that act as a unit.

  4. Examples of Molecules • Ozone (O3) • Carbon Dioxide (CO2) • Glucose (C6H12O6) • Water (H2O)

  5. These compounds tend to have relatively low melting and boiling points. • In most are composed of two or more nonmetals. • Many exist as gases or liquids at room temperature. • Compounds composed of molecules are called molecular compounds.

  6. Ions and Ionic Compounds • Many compounds are composed of particles called ions. Ions are atoms or groups of atoms that have a positive or negative charge. • Ions form when atoms lose or gain electrons. • When an atom loses electrons the charge is positive. • When an atom gains electrons the charge is negative.

  7. Cation vs. Anion • A cation is any atom or group of atoms that has a positive charge. • An anion is any atom or group of atoms that has a negative charge.

  8. Naming Ions • A positive ion will have the same name as the atomic form of the element with the word ion tagged on the end. • A negative ion will have the same root name as the atomic form of the element with a suffix of –ide and the word ion tagged on the end.

  9. Ex #1: Give the name and symbol of the ion formed when: • a selenium atom gains two electrons Se2-Selenide ion • a gallium atom loses three electrons Ga3+ Gallium ion • a magnesium atom loses two electrons. Mg2+ Magnesium ion

  10. Ex #2:How many electrons are lost or gained in forming each ion? • Li+ • One electron is lost • N3- • Three electrons are gained • Fe2+ • Two electrons are lost

  11. Compounds composed of cations and anions are called ionic compounds. • Ionic compounds are usually composed of metal cations and nonmetal anions. They are referred to as formula units. • Usually solid crystals at room temperature. • Melt at high temperatures.

  12. Ex #3: Tell whether the following compounds are ionic or molecular. • AlI3 • ionic • CaH2 • ionic • Cl2O • molecular • I2 • molecular • ZnO • ionic • CuC2H3O2 • ionic

  13. Section 6.1 Introduction to Chemical Bonding • Did we meet our Objectives? • Distinguish between ionic and molecular compounds • Define cation and anion and relate them to metal and nonmetal

  14. Section 6.2 Representing Chemical Compounds • Objectives: • Distinguish among chemical formulas, molecular formulas, and formula units • Use experimental data to show that a compound obeys the law of definite proportions.

  15. Chemical Formulas • A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of the substance. • Some elements chemical formulas must be represented as diatomic: • H2, F2, O2, N2, Cl2, Br2, and I2

  16. Molecular Formulas • A molecular formula shows the kinds and numbers of atoms present in a molecule of a compound. • Although a molecular formula shows the composition of a molecule, it tells you nothing about the molecule’s structure.

  17. Formula Units • Formula unit – the lowest whole-number ratio of ions in a compound. • This cannot be used to explain molecular compounds

  18. The Law of Definite Proportions • Law of Definite Proportions – regardless of the amount, a compound is always composed of the same elements in the same proportion by mass. • The proportions are found by calculating the percent by mass.

  19. Percent by Mass • What is the percent by mass of the elements that make up water? H2O • (mass of hydrogen / mass of water) x 100 • (mass of oxygen / mass of water) x 100 • (2.02 g / 18.02 g) x 100 = 11.21 % Hydrogen • (16.00 g / 18.02 g) x 100 = 88.79 % Oxygen

  20. Ex #3. Find the percent by mass for each element in the following compounds. • NaCl • CO2

  21. Law of Definite Proportion Lab • Nuts & Bolts – In your groups, complete the law of definite proportion task.

  22. The Law of Multiple Proportions • Law of Multiple Proportions – The different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

  23. Ex #4 Lead forms two compounds with oxygen. One compound contains 2.98 of lead combined with 0.461 g of oxygen. The other compound contains 9.89 g of lead combined with 0.736 g of oxygen. What is the lowest whole-number mass ratio of lead in the two compounds that combines with a given mass of oxygen? Take the mass of lead and divide it by the mass of oxygen for each compound. The ratios should be whole numbers! • Compound A = (2.98 g Pb / 0.461 g O) = 6.46 • Compound B = (9.89 g Pb / 0.736 g O) = 13.44 B:A = 13.44:6.46 = 2:1 Compound B has twice as much lead as Compound A!

  24. Ex #5. Carbon reacts with oxygen to form two compounds. Compound A contains 2.41 g of carbon for each 3.22 g of oxygen. Compound B contains 6.71 g of carbon for each 17.9 g of oxygen. What is the lowest whole-number mass ratio of carbon that combines with a given mass of oxygen? • Compound A = (2.41 g C / 3.22 g O) = 0.748 • Compound B = (6.71 g C / 17.9 g O) = 0.375 A:B = 0.748:0.375 = 2:1 Compound A has twice as much carbon as Compound B!

  25. Law of Multiple Proportion Lab • Nuts & Bolts – In your groups, complete the law of multiple proportion task.

  26. Section 6.2 Representing Chemical Compounds • Did we accomplish our objectives? • Distinguish among chemical formulas, molecular formulas, and formula units • Use experimental data to show that a compound obeys the law of definite proportions.

  27. Section 6.3 Ionic Charges • Objectives: • Use the periodic table to determine the charge on an ion • Define a polyatomic ion and give the names and formulas of the most common polyatomic ions

  28. Monatomic Ions • Monatomic ions – ions consisting of only one atom. The ionic charge is often determined by using the periodic table.

  29. Table 6.2 Tend not to form ions. Tend not to form ions.

  30. Naming cations with more than one charge. • There are two methods for naming cations with more than one charge: • Stock System • More common method • Uses Roman numerals to indicate the charge. • Classical System • Older, less preferred method • The root word is used with a suffix of: • ous: lower of the two charges • ic: higher of the two charges

  31. Stock System • Name the following cations using the stock system: • Cu+ • Copper (I) ion • Cu2+ • Copper (II) ion • Sn4+ • Tin (IV) ion • Co3+ • Cobalt (III) ion

  32. Classical System • Name the following cations using the classical system: • Cu+ • Cuprous ion • Cu2+ • Cupric ion • Sn4+ • Stannic ion • Co3+ • Cobaltic ion

  33. Ferris Wheel

  34. What is the charge of the ion typically formed by each element? (For transition metals with more than one common ionic charge, the number of electrons lost is indicated.) • Sulfur • 2- • Lead, 4 e- lost • 4+ • Strontium • 2+ • Argon • No ion formed • Bromine • 1- • Copper, 1 e- lost • 1+

  35. A few transition metals have only one ionic charge. The names of these cations do NOT have a Roman numeral. • Ag+ • Cd2+ • Zn2+

  36. Polyatomic Ions • Polyatomic ions are tightly bound groups of atoms that behave as a unit and carry a charge. • Most polyatomic ions end in –ite or –ate. • Exceptions include: ammonium, cyanide, and hydroxide. • Table 6.4 lists common polyatomic ions.

  37. By examining the relationship among polyatomic ions with an –ite/-ate pair, one can see that the –ate endings have one more oxygen atom than the –ite endings. • NO2- = nitrite • NO3- = nitrate

  38. Section 6.3 Ionic Charges • Did we meet our objectives? • Use the periodic table to determine the charge on an ion • Define a polyatomic ion and give the names and formulas of the most common polyatomic ions

  39. Section 6.4 Ionic Compounds • Objectives: • Apply the rules for naming and writing formulas for binary ionic compounds. • Apply the rules for naming and writing formulas for ternary ionic compounds.

  40. Writing Formulas for Binary Ionic Compounds • Compounds composed of two elements are called binary compounds. Binary compounds can be either ionic or molecular.

  41. Binary Ionic Compounds • Binary Ionic Compounds • Compounds composed of two different elements, a cation and an anion. • The total number of positive and negative charges must equal. • The cation comes first, then the anion. • Use subscripts to determine the number of atoms of each element.

  42. Make a binary ionic compound containing aluminum and sulfur. • Al3+ S2- Both charges must equal zero. Since 3+ and 2- do not equal zero, we need to add additional atoms of each. Al3+ S2- S2- Al3+ S2- Al2S3

  43. Write formulas for these binary ionic compounds. • Copper (II) sulfide • CuS • Potassium nitride • K3N • Sodium iodide • NaI • Calcium chloride • CaCl2

  44. Write formulas for compounds formed from these pairs of ions. • Ba2+, S2- • BaS • Li+, O2- • Li2O • Ca2+, N3- • Ca3N2 • Cu2+, I- • CuI2

  45. Naming Binary Ionic Compounds • Nomenclature is a naming system. • The cation is named first (Roman numerals are needed if there is more than one charge), then the anion is named second (remember the anion will have a suffix of –ide). • Al2O3 aluminum oxide • ZnCl2 zinc chloride • Ca3P2 calcium phosphide

  46. Name the following binary ionic compounds. • CoI2 • Cobalt (II) iodide • Cs2O • Cesium oxide • ZnS • Zinc sulfide • FeO • Iron (II) oxide

  47. Ternary Ionic Compounds • Ternary Ionic Compound – a compound that contains atoms of three different elements. • Ternary ionic compounds usually contain a polyatomic ion.

  48. Rules for making an ionic compound with a polyatomic ion. 1. Write the symbols for the ions side by side with the cation first. Ca2+ NO3- 2. Cross over the charges to give subscripts. Add parentheses around the polyatomic ion if there is more than one. Ca(NO3)2

  49. Write formulas for these ternary ionic compounds. • Potassium sulfate • K2SO4 • Magnesium hydroxide • Mg(OH)2 • Calcium phosphate • Ca3(PO4)2 • Potassium carbonate • K2CO3

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