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Biochemistry (timberlake), chapter 4

Biochemistry (timberlake), chapter 4. Why do elements form compounds? How do elements form compounds?. The Octet Rule. Only atoms with filled valence shell s and p orbitals are stable. For H & He, the 1 st shell is the valence shell—stable with 2 valence electrons in an s orbital

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Biochemistry (timberlake), chapter 4

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  1. Biochemistry (timberlake), chapter 4 Why do elements form compounds? How do elements form compounds?

  2. The Octet Rule Only atoms with filled valence shell s and p orbitals are stable. For H & He, the 1st shell is the valence shell—stable with 2 valence electrons in an s orbital For all other elements, 8 valence electrons are needed to fill s & p orbitals of the valence (highest energy level) shell

  3. Noble gases do not react They already have stable filled valence energy level s and p orbitals. Other elements react to attain a stable valence shell.

  4. 10 Chemical compounds are groups of atoms held together by chemical ________. Chemical compounds are more stable than individual atoms (except for n_______ gas atoms which have stable ---filled—valence electron shells. • Chemical compounds allow atoms to obey the “_________ rule”. (2 electrons in the outer electron shell in H and He, but 8 for other elements.

  5. 10 Chemical compounds are groups of atoms held together by chemical bonds. Chemical compounds are more stable than individual atoms (except for noble gas atoms which have stable ---filled—valence electron shells. • Chemical compounds allow atoms to obey the “octet rule”. (2 electrons in the outer electron shell in H and He, but 8 for other elements.

  6. 11 C_________ f_________ show the numbers of different kinds of atoms bonded together in a single formula unit of a compound • NaCl ______ Na ion bonded to one Cl ion • Why do we know it’s composed of ions? Because Na is a _______—an electron donor—and Cl is a __________—an electron acceptor if a metal is present to give it an electron.

  7. 11 Chemical formulas show the numbers of different kinds of atoms bonded together in a single formula unit of a compound • NaCl one Na ion bonded to one Cl ion • Why do we know it’s composed of ions? Because Na is a metal—an electron donor—and Cl is a nonmetal—an electron acceptor if a metal is present to give it an electron.

  8. Elements are either metals, metalloids, or nonmetals.

  9. The reason that so much emphasis is placed on whether an element is metallic or nonmetallic is that this determines electronegativity—and electronegativity controls bonding strategy.

  10. Major Strategies for Increasing Chemical Stability via Chemical Bonding Ionic bonding metal atoms donate valence electrons to nonmetal atoms Covalent bonding Nonmetal atoms share valence electrons with other nonmetal atoms

  11. 12 Atoms in compounds are held together by chemical bonds—either i______ or c_______.

  12. 12 Atoms in compounds are held together by chemical bonds—either ionic or covalent.

  13. Electronegativity Controls the type of bond that forms 0< 0.5 nonpolar covalent 0.5—1.7 polar covalent • 1.7 ionic • Ionic: metal, nonmetal • Covalent: nonmetals bonded together

  14. Ionic compounds form when metal atoms come near nonmetal atoms. Both atoms attain more stable electron configurations. http://visionlearning.com/library/flash_viewer.php?oid=1349&mid=55 http://www.youtube.com/watch?v=WXyFMJ0eJA0&NR=1 http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/reaction/bonding1.html

  15. Covalent compounds are formed when nonmetals come near each other and share (too little electronegativity difference to transfer electrons) valence electrons. http://web.visionlearning.com/custom/chemistry/animations/CHE1.7-an-H2Obond.shtml

  16. http://www.youtube.com/watch?v=QqjcCvzWwww&feature=related http://www.youtube.com/watch?v=Ibr63AjnEoQ&feature=

  17. Electron Dot Structures show an element’s symbol surrounded by it’s valence electrons

  18. Ionic compounds form when metals donate valence electrons to nonmetal atoms. Both become more stable.

  19. Members of the same family (group) have the same # Lewis dots.

  20. Metal atoms form + ions by losing valence electrons Na• → Na+1

  21. Nonmetal atoms form - ions by gaining valence electrons to complete their existing highest energy level

  22. Ion • Charged particle with more or fewer electrons than protons • Gain or lose electrons, not protons • Changing the number of protons would change the identity of the atom! • Cl 17 p+, 17 e- Cl1- 17 p+, 18 e-

  23. Sodium Chlorine Sodium Chloride

  24. Ionic bonds Negative ions are attracted to positive ions The ions are more stable than the unreacted ions because they are more stable

  25. Ionic Compounds • Metals and nonmetals present • High melting points, brittle, crystals at room temperature (specific shape), most soluble in water • Conduct electricity when dissolved in water (electric current is charges moving from - to +)

  26. Same chemical family (group) ↔same number valence electrons

  27. Oxidation number: The charge typical of an element when it’s atoms lose or gain electrons to form a valence s and p octet. Oxidation numbers of elements can be predicted from their periodic table position. Family metal nonmetal 1 +1 2 +2 13 +3 -5 14 +4 -4 15 +5 -3 16 +6 -2 17 -1 18 0

  28. Ionic Bond • Transfer of electrons creates oppositely charged ions, which are attracted to each other • BOTH a gain and a loss of electrons occur in the formation of an ionic bond • MgCl2 • Mg has 2 valence electrons, so it must lose 2 to be stable Mg2+ • Cl has 7 valence electrons, so it must gain 1 to be stable Cl- • For Mg to lose both electrons, it needs 2 chlorine atoms, so the formula is MgCl2

  29. Figure 2-3 Ionic Bonding 13 Ionic bonds: attraction of negative ions to positive ions because a metal donates its __________ to a nonmetal atom, forming stable ions with complete _________ shell octets. Section 2-1 Sodium ion (Na+) Chloride ion (Cl-) Sodium atom (Na) Chlorine atom (Cl) Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1

  30. Figure 2-3 Ionic Bonding 13 Ionic bonds: attraction of negative ions to positive ions because a metal donates its electrons to a nonmetal atom, forming stable ions with complete valence shell octets. Section 2-1 Sodium ion (Na+) Chloride ion (Cl-) Sodium atom (Na) Chlorine atom (Cl) Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1

  31. Figure 2-3 Ionic Bonding 14 _____are atoms carrying a charge after losing or gaining valence electrons. Section 2-1 Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-) Transfer of electron Protons +17 Electrons -18 Charge -1 Protons +11 Electrons -11 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -17 Charge 0

  32. Figure 2-3 Ionic Bonding 14 Ions are atoms carrying a charge after losing or gaining valence electrons. Section 2-1 Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-) Transfer of electron Protons +17 Electrons -18 Charge -1 Protons +11 Electrons -11 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -17 Charge 0

  33. 15. True orFalse. ______Atom that loses electrons becomes a positive ion. (sodium atoms have 11 protons in the nucleus and 11 neutrons and 11 electrons. Sodium ions have 11 protons, 11 neutrons, and 10 electrons).

  34. 15. True orFalse. False_Nonmetal atoms that gain electrons becomes positive ions. (chlorine atoms have 17 protons in the nucleus and 18 neutrons and 11 electrons. Chlorine ions have 17 protons, 18 neutrons, and 18 electrons).

  35. Crisscross method: quick way to determine formula for ionic compound • When using the crisscross method, remember: • Transfer the NUMBER but NOT the sign of the charge from one element to the other • Reduce to the lowest whole number ratio • Practice with this website! • http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/reaction/bonding1.html

  36. Writing Ionic Formulas (continuation of #8 and #9) • Find the # of valence electrons • Determine the charge • Make sure the compound is NEUTRAL- no charge • Use the crisscross method • Reduce to lowest whole number ratio

  37. Crisscross method • When using the crisscross method to predict ionic compound chemical formulas: • Transfer the NUMBER but NOT the sign of the charge from one element to the other • Reduce to the lowest whole number ratio • Na1+Cl1- Na1Cl1 NaCl sodium chloride • Ca2+F1- CaF2 CaF2 calcium fluoride • Li1+O2- Li2O1 Li2O lithium oxide

  38. 11 C_________ f_________ show the numbers of different kinds of atoms bonded together in a single formula unit of a compound • NaCl ______ Na ion bonded to one Cl ion • Why do we know it’s composed of ions? Because Na is a _______—an electron donor—and Cl is a __________—an electron acceptor if a metal is present to give it an electron.

  39. 11 Chemical formulas show the numbers of different kinds of atoms bonded together in a single formula unit of a compound • NaCl one Na ion bonded to one Cl ion • Why do we know it’s composed of ions? Because Na is a metal—an electron donor—and Cl is a nonmetal—an electron acceptor if a metal is present to give it an electron.

  40. Slide 8 Compounds are of 3 major categories: binary ionic, polyatomic ionic, & covalent Look for the pattern in the binary ionic compounds below to define Binary ionic compound (_______________________________________) • 2Na (s) + Cl2(g)  2NaCl(s) http://video.google.com/videoplay?docid=-3746358316523224177&ei=4KLaSN36PJGu-AGTkcilCw&q=sodium+reaction+chlorine&vt=lf MgCl2 magnesium chloride K2O potassium oxide Al2O3 aluminum oxide InF3 indium fluoride Rb3N rubidium nitride Cs4C cesium carbide Guess the rule for naming binary ionic compounds: ___________________________________________

  41. define Binary ionic compound one metal element & one nonmetal element joined by transfer of valence electrons from the metal to the nonmetal atoms. 2Na (s) + Cl2(g)  2NaCl(s) MgCl2 magnesium chloride K2O potassium oxide Al2O3 aluminum oxide InF3 indium fluoride Rb3N rubidium nitride Cs4C cesium carbide rule for naming binary ionic compounds: Name metal without change, name the nonmetal then change the ending of the nonmetal’s name to -ide

  42. Websites useful for practicing concepts from 2.1 to 2.3 Identifying metals versus nonmetals versus metalloids www.ualr.edu/rebelford/chem1402/q1402/X1/c2/2-5/2-5.htm Animated tutorial for naming compounds given their formulas www.quia.com/mc/65800.html

  43. Formative assessment binary ionic compounds 1 Write the chemical formula for a compound called: A strontium oxide B lead chloride C iron (III) oxide D iron (II) sulfide • Write the name for A MgCl2 B CrO C Zr3N2 3 Nonmetals in family 17 all have _____ valence electrons and form ions with ___ charge. Metals in family 16 have ____ valence electrons and form ions with ___ charge.

  44. 1A strontium oxide Sr2+O2- Sr2O2SrO B lead chloride if lead (II) chloride PbCl2 if lead (IV) chloride PbCl4 C iron (III) oxide Fe2O3 D iron (II) sulfide FeS • Write the name for A MgCl2 Magnesium chloride B CrOchromium (II) oxide C Zr3N2 Zinc (II) nitride 3 Nonmetals in family 17 all have_7_ valence electrons and form ions with _-1_ charge. Metals in family 16 have 6_ valence electrons and form ions with _+6 charge.

  45. Polyatomic ionic compounds • Polyatomic ions are groups of covalently bonded atoms that act as a single ion Know these before the final exam Phosphate PO43- hydroxideOH1- Sulfate SO42- cyanide CN1- Carbonate CO32- Nitrate NO31- Acetate CH3COO1- Ammonium NH41+

  46. Criss cross rule applies—use parenthesis when… Na 1+PO43- Na 1+3PO43- 1 Na3PO4 K1+SO42- K1+ 2SO42- 1 K2SO4 Mg2+CO32- Mg2+ 2CO32- 2 Mg2CO32 Al3+NO31- Al3+ 1NO31- 3 Al (NO3) 3 Pb4+CH3COO1- Pb4+ 1CH3COO1- 4 Pb(CH3COO)4 NH41+ CO32- NH41+ 2CO32- 1(NH4)2CO3

  47. Nomenclature for polyatomic ionic compounds Name monoatomic metals without change Name polyatomic ions without change Name monoatomic nonmetals then change ending to ide Na3PO4 sodium phosphate NH4Cl ammonium chloride K2SO4 potassium sulfate MgCO3 magnesium carbonate Al(NO3) 3 aluminum nitrate Pb(CH3COO)4 lead acetate

  48. 13 _________ bonds form when nonmetal atoms share electrons to fill their valence o_______, linking atoms because both nuclei attract the shared electrons. The dots around the nuclei of each atom represent ___________ __________. The dots in between two nuceli in the formulas are ________________ by the two atoms. The formulas for the c_________ compounds formed below are _____, ______, ______, and ________.

  49. 13 Covalent bonds form when nonmetal atoms share electrons to fill their valence octets, linking atoms because both nuclei attract the shared electrons. The dots around the nuclei of each atom represent valence electrons. The dots in between two nuceli in the formulas are shared by the two atoms. The formulas for the covalent compounds formed below are H2, F2, CO2, and CF4.

  50. 16 M__________ (Not ionic compounds!) form when atoms are joined with covalent bonds.

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