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Section IV: Moving Electrons

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Section IV: Moving Electrons

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  1. Section IV: Moving Electrons • Lesson 17 Technicolor Atoms • Lesson 18 Life on the Edge • Lesson 19 Noble Gas Envy • Lesson 20 Getting Connected • Lesson 21 Salty Eights • Lesson 22 Isn’t It Ionic? • Lesson 23 Alchemy of Paint • Lesson 24 Shell Game

  2. Lesson 17: Technicolor Atoms • Flame Tests

  3. ChemCatalyst • These drawings are models that show solid copper, solid copper chloride, and aqueous copper chloride as collections of atoms. • 1. Describe each model. • 2. What is similar about each model? What is different? Cu(s) Solid copper CuCl2(s) Solid copper (II) chloride CuCl2(aq) Aqueous copper (II) chloride

  4. Key Question • What evidence is there that certain atoms are present in a compound?

  5. You will be able to: • conduct a flame test and use the results to determine the identity of a compound • interpret evidence of the presence of certain atoms within compounds

  6. Prepare for the Lab • Work in groups. • You will be using chemicals and fire today. Follow safety instructions. • Wear safety goggles. • Tie back long hair and remove dangling jewelry. • Roll up long sleeves and keep clothing away from flames. • Locate the eye wash, fire blanket, and fire extinguisher before starting the lab.

  7. Discussion Notes • The metal element in each chemical formula appears to be responsible for the flame colors. • Only certain elements produce colorful flames. • Flame test: A test used in the laboratory to look for the presence of certain metal atoms. A sample of a compound is heated in a flame, and the resulting color is noted.

  8. Discussion Notes (cont.) • Elements and compounds are collections of atoms. • The only way to change one atom into another is to change the nucleus through a nuclear reaction.

  9. Discussion Notes (cont.) • Sodium Atom, Na

  10. Discussion Notes (cont.) • The illustration indicates that the flame colors are associated with movements of the electrons within the sodium atom. • Bohr’s model of the atom came directly from evidence similar to that produced in class today.

  11. Wrap Up • What evidence is there that certain atoms are present in a compound? • Many metal atoms produce a characteristic colored flame when compounds containing those atoms are heated in a flame. • Flame tests are evidence that elements and compounds are collections of atoms.

  12. Check-in • Predict the flame colors produced when heating these substances. Explain your thinking. • • copper (II) carbonate • • calcium chloride

  13. Lesson 18: Life on the Edge • Valence and Core Electrons

  14. ChemCatalyst • What do you notice about the number of spokes on the circles? • The spokes represent electrons. Do the spokes represent the total number of electrons? Explain your thinking.

  15. Key Question • Why do elements in the same group in the periodic table have similar properties?

  16. You will be able to: • create a shell model diagram of an atom, placing the correct number of electrons in the correct shells • explain the difference between a valence electron and a core electron • describe the patterns in the periodic table associated with electron arrangements

  17. Prepare for the Activity • Work in pairs.

  18. Prepare for the Activity (cont.) • The Shell Model The surface of each sphere represents an area where an electronor a group of electronsis most likely to be found.

  19. Prepare for the Activity (cont.) • Electron shells are the levels around the nucleus where electrons can be found. Sodium and magnesium have electrons in three electron shells.

  20. Discussion Notes • The atomic number of an element is the same as the total number of electrons. • The period (row) number of the element is the same as the number of electron shells. • For main-group elements, the group number of the element is the same as the number of electrons in the outermost shell.

  21. Discussion Notes (cont.) • Table of Valence and Core Electrons

  22. Discussion Notes (cont.) • Valence shell: The outermost electron shell in an atom. • Valence electrons: The electrons located in the outermost electron shell of an atom. • Core electrons: All other electrons in an atom besides the valence electrons.

  23. Discussion Notes (cont.) • The arrangement of electrons in their shells is highly predictable. • The numbers of core electrons also exhibit patterns across each row of the periodic table.

  24. Wrap Up • Why do elements in the same group in the periodic table have similar properties? • Electrons occupy distinct areas around the nucleus called electron shells. The arrangement of electrons in these shells is highly predictable. • For main group elements, elements in the same group have the same number of valence electrons. • The number of valence electrons increases across a period. • The number of shells and the number of core electrons increase as you go down a group.

  25. Check-in • Provide each piece of information for element 34. • a. The element’s name and symbol. • b. The total number of electrons in an atom of this element. • c. The number of core electrons in an atom of this element. • d. The number of valence electrons. • e. The group number for this element. • f. The names of other elements with the same number of valence electrons.

  26. Lesson 19: Noble Gas Envy • Ions

  27. ChemCatalyst • Chemists have found that metal atoms transfer electrons to nonmetal atoms when they form compounds. Examine the shell model showing how a lithium atom might transfer an electron to a fluorine atom. • What effect does this electron transfer have on the charge of each atom? • What element does each atom resemble after the electron has been transferred?

  28. Key Question • How is chemical stability related to the arrangements of electrons in atoms?

  29. You will be able to: • explain that an ion is formed when an atom loses or gains electrons and state the difference between a cation and an anion • determine the charge on an ion based on an atom’s placement in the periodic table • explain the relationship between ion charge and valence electrons

  30. Prepare for the Activity • Work in groups of eight. • Ion: An atom (or group of atoms) that has a positive or negative charge because it has lost or gained electrons.

  31. Discussion Notes • The table of arranged ion cards shows that the charges on ions are quite predictable.

  32. Discussion Notes (cont.) • When electrons are removed from or added to an atom, the rest of the atom stays the same. • The charge on an ion is noted with a superscript.

  33. Discussion Notes (cont.) • Cation: An ion with a net positive charge. Usually these are formed from metal atoms. • Anion: An ion with a net negative charge. Usually these are formed from nonmetal atoms.

  34. Discussion Notes (cont.) • Electron arrangementsof atoms in ioniccompounds resemblenoble gases.

  35. Discussion Notes (cont.) • Atoms tend to lose or gain electrons to attain the electron arrangement of a noble gas.

  36. Wrap Up • How is chemical stability related to the arrangements of electrons in atoms? • When atoms gain or lose electrons, they form ions. Ions are atoms that carry a net positive or net negative charge. • When atoms lose electrons, they have a positive charge and are called cations. • When atoms gain electrons, they have a negative charge and are called anions. • Ions have electron arrangements resembling those of the noble gas atoms.

  37. Check-in • Draw a shell model for calcium, Ca, showing the arrangement of its electrons. • What would have to happen for an atom of calcium to have an electron arrangement like that of a noble gas? Explain.

  38. Lesson 20: Getting Connected • Ionic Compounds

  39. ChemCatalyst • Metal elements combine with the nonmetal element chlorine, Cl, to form compounds. The formulas are given in the tables. • Compare the three tables. What do you notice? • Predict the formula of a compound formed between lithium, Li, and chlorine, Cl. Which table would you put it in?

  40. Key Question • How can valence electrons be used to predict chemical formulas?

  41. You will be able to: • predict the chemical formulas of compounds that will form between metal and nonmetal atoms • explain how an ionic compound forms and determine whether it follows the rule of zero charge

  42. Prepare for the Activity • Work in pairs. • Ionic compound: An ionic compound is a compound composed of positive and negative ions, formed when metal and nonmetal atoms combine.

  43. Discussion Notes Mg2+ + Cl–+ Cl–produces MgCl2 with zero charge.

  44. Discussion Notes (cont.) • Metal and nonmetal elements combine to form ionic compounds. • The electron arrangements of the cations and anions resemble the arrangements of a noble gas atom.

  45. Discussion Notes (cont.) • The rule of zero change can be used to determine the chemical formulas of ionic compounds. • Rule of zero charge: In an ionic compound, the positive charges on the metal cations and the negative charges on the nonmetal anions sum to 0.

  46. Discussion Notes (cont.) • Chemical Formulas of Ionic Compounds

  47. Discussion Notes (cont.) • The number of electrons associated with the atoms of an ionic compound generally totals 8 or a multiple of 8.

  48. Wrap Up • How can valence electrons be used to predict chemical formulas? • Metal atoms and nonmetal atoms combine to form ionic compounds. • In ionic compounds, the metal is considered a cation, and the nonmetal is considered an anion. • The charges on the cations and the anions in ionic compounds sum to 0. • Metal atoms and nonmetal atoms usually combine in ratios that result in a total of eight valence electrons or a multiple of eight valence electrons.

  49. Check-in • What elements will combine with strontium, Sr, in a 1:1 ratio? Explain your thinking.

  50. Lesson 21: Salty Eights • Formulas for Ionic Compounds