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Discussion: Lewis Structures and VSEPR Theory

Discussion: Lewis Structures and VSEPR Theory. OBJECTIVE: Students Will Understand Why Elements Form Bonds With Other Elements. What are valence electrons?. Electrons in the highest energy level Elements in the same group on the periodic table have the same number

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Discussion: Lewis Structures and VSEPR Theory

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  1. Discussion: Lewis Structures and VSEPR Theory OBJECTIVE: Students Will Understand Why Elements Form Bonds With Other Elements

  2. What are valence electrons? • Electrons in the highest energy level • Elements in the same group on the periodic table have the same number • A valence of 8 electrons is called a octet • Atoms try to get a valence of 8 electrons

  3. Not all elements try to get a valence of eight electrons • Hydrogen needs only two. • Beryllium needs on four • Boron needs only six. • However, most elements like to have eight electrons in their valence shell.

  4. How the Valence Electrons Fit Around Group #1 Atoms

  5. Valence Electrons for Group #2

  6. Valence for the rest

  7. How Atoms Gain an Octet by Losing Electrons • Calcium atom loses two electrons to achieve an octet

  8. How Atoms Gain an Octet by Gaining Electrons • Chlorine has seven electrons. It gains one electron to make eight. The addition of an electron make the ion negative.

  9. Nobel Elements already have an octet. • Neon for example has 10 electrons • Notice it already has an octet. That is why it doesn't react with other elements

  10. Ions almost always have an octet • Na+ ion for example, has 10 electrons just like Neon • 2 8Na+ | | lost 1 • 2 8 • O2- | | gained 2 • 2 8 • Ne | | Atoms try to get this electron configuration

  11. AlCl3 • Draw on board

  12. PCl3 • Count all the valance electrons • Determine the central atom. • Connect the ligands to the central atom.

  13. VSEPR Theory • Valence • Shell • Electron • Pair • Repulsion

  14. The VSEPR Theory • Explains the geometric shape of a molecule based solely on the repulsion of electron pairs around the central atom.

  15. Geometric Shapes • Linear • Planer Triangular • Tetrahedral

  16. Polar molecules • Molecules that are unbalanced are polar.

  17. Planer Triangular • Draw SO2 • Total Electrons = 18 • Central Atom = S • Connect the two oxygen atoms to the central atom. Subtract 2 for each bond. • Put six around the O. Put the extra around the central atom. • Make the legends double share until all have octets.

  18. The Shape of SO2 • Notice there are 3 pairs of electrons around the central atom.

  19. The Shape of H2O • Draw the Lewis structure for Water

  20. NH3 • Draw the Lewis structure for ammonia

  21. CH4 • Draw the Lewis structure for methane

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