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Chapter 22

Chapter 22. Compounds Between Metals and Non-Metals – the Ionic Bond Called Salts. Near the boundary between metals and non-metals. Conduction and valence bands do not overlap. conduction band. band gap. valence band. Band Gap. semiconductors.

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Chapter 22

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  1. Chapter 22 Compounds Between Metals and Non-Metals – the Ionic Bond Called Salts

  2. Near the boundary between metals and non-metals Conduction and valence bands do not overlap conduction band band gap valence band Band Gap semiconductors

  3. E= h times frequency; c= wavelength times frequency Red longer wavelength means lower frequency, lower energy.

  4. Red photons are emitted from a warm LED; orange photons are emitted when the LED is very cold. What happened? • The band gap shrinks when the semiconductor gets cold. • No “red” electrons get kicked upstairs to fall back down. • The band gap increases when the semiconductor gets cold.

  5. Did you read chapter 22 before coming to class? Or do you have a Halloween costume? • Yes • No

  6. Which element will react with water in a way most similar to Na? • O • Cl • Li • Hg

  7. Which of the following has the highest ionization energy • Na (Z=11) • Al (Z=13) • Cl (Z=17) • Ne (Z=10)

  8. Ionization Energies • Nobel gasses have largest ionization energies. • Alkali metals have the least.

  9. Compare and Contrast:Ionic Compounds vs Metals • Network Solids • High melting T’s • Brittle solids • Don’t conduct heat and electricity in solid • Often colorless and usually transparent in big chunks (White when powdered) • Network Solids • High melting T’s • Malleable • Good conductors of heat and electricity in solid • Opaque Why??? Many closely spaced energy levels with mobile electrons WHY?

  10. Compare and Contrast:Metals vs Non-Metals • Non-metals • Small atoms • Many valence electrons • High ionization energies • Metals • Large atoms • Few valence electrons • Low ionization energies For a given row Why do metals and non-metals react? Principles of reactivity: materials react to lower energy and increase entropy of universe

  11. How can energy be lowered? Metals lose valence electrons Non-metals gain valence electrons Transfer of electron from Na to Cl is downhill energetically Energy levels not drawn to scale. Cl levels much lower in energy!

  12. What about entropy change? • 2Na + Cl2 = 2NaCl + lots of heat and light Na – speck Cl2 yellow gas sand at bottom Quicktime Video of reaction Heat and light – cause an increase in entropy of the surroundings

  13. Neutral Cl atom neutral atom Negative Cl ion Positive ion What are the products? IONS Negatively charged Chloride ions 35 protons, 36 electrons Positively charged Sodium ions (11 protons, 10 electrons) Electrons belong to individual ions; they are not shared among ions.

  14. NaCl Na2O Al2O3 Ions: same charges and similar sizes Ions: different charges and sizes Ions: similar sizes, but different charges Examples of Ionic Compounds Describe the structure of each compound: Do ions of one type cluster together? What type of ion immediately surrounds a given ion? How do the answers to these two questions relate to the electric force law? What prediction could you make about the arrangement of ions in any ionic compound?

  15. A. 0 of 5 B. 10 Answer Now Which structure is the form adopted by Al2O3 in nature? • 1 • 2

  16. 0 of 5 10 Answer Now What factor most likely prohibits this structure? • Strong repulsive forces between negative O ions and between positive Al ions • Not electrically neutral • Low entropy organization

  17. Compare & Contrast Energy Levels IONIC COMPOUND ENERGY LEVELS Metal Energy Levels many closely spaced levels spread out over many nuclei few levels -- spaced very far apart

  18. Ionic Salts Transparent in Visible Region of Spectrum – But absorb in UV (exception: salts containing certain transition metal ions absorb in visible region.) Metals Opaque – absorb in IR, Visible and UV Energy Levels Explain l20newcrystal.swf l20photon.swf

  19. + + + + + + + + + Compare and ContrastElectron Locations & Mobilities IONIC COMPOUNDS METALS AND ALLOYS Electrons – localized on individual nucleus (spherically shaped electron clouds in most ions) Sea of Electrons – mobile; electron density is spread out over many nuclei, delocalized.

  20. How does the model explain properties of salts (ionic compounds) ? • High melting and boiling temperatures? • Strong attractions between + and – ions • Attractive forces act over fairly large atomic distances • Brittleness? • Strong repulsions when ions with like charge come together; material shatters to relieve the stress.

  21. ELECTRICAL CONDUCTIVITY: Flow of electricity requires charge carriers that are free to move. • In solid, ions are fixed rigidly in place. No Current can flow! • Melting frees up ions so that they can move, completing the electrical • circuit. • Dissolving salt in water also frees up ions. Current flows!

  22. Absorbs blue photons Absorbs green photons Doesn’t absorb red photons: reflects red Even More Properties • Why are some ionic materials colored? • Because they contain “transition” metals with more energy levels for electrons • Example: Ruby

  23. Unreactive noble gases don’t form ions. Non-metals GAIN enough valence electrons to become “noble”. Metals LOSE their valence electrons. What Ions Usually Form? Using the Periodic Table to make predictions.Valence Electrons of Main Group Elements

  24. The octet rule • Atoms will most likely form an ion that has the ns2np6 configuration of the closest noble gas atom. • Metals take on this configuration by losing electrons • Non-metals take on this configuration by gaining electrons

  25. Chlorine and Fluorine will form the same types of compounds since their valence electrons are the same number and same orbital type. 3d 3p 3s 3d 3p 3s 2p 2p 2s 2s 1s 1s Families 9F 17Cl

  26. When Mg loses its two electrons, it has the same valence electron configuration as • He, 1s2 • Ne, 2s22p6 • Ar, 3s23p6 • Kr, 4s24p6

  27. When Br gains one electron, it has the same valence electron configuration as • He, 1s2 • Ne, 2s22p6 • Ar, 3s23p6 • Kr, 4s24p6

  28. Beryllium (Be) will most likely form an ion with what charge? • -1 • -2 • +1 • +2

  29. What would the chemical formula for magnesium fluoride (a salt of Mg and F) be? • MgF • Mg2F • MgF2 • MgF3

  30. NaCl KBr MgF2 Al2O3 Na+1 and Cl-1 K+1 and Br-1 Mg+2 and F-1 Al+3 and O-2 Ionic compounds are neutral (no net charge). What are the ionic charges in the following compounds?

  31. Naming convention for salts • The metal comes first with its name unchanged • The nonmetal comes second, with the suffix “ide” appended

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