Ch400Ch7LN2 - Lewis Structures(Lewis Dot Structures or Electron Dot Structures You learned how to write electron configurations and Noble Gas

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Lewis Structures (Lewis Dot Structures or Electron Dot Structures) • You learned how to write electron configurations and Noble Gas electron configurations. • You also learned that the valence electrons are the electrons on the highest energy level, and you learned how to count how many valence electrons an atom has (in Groups 1-2, 13-18). • And you learned the octet rule which states that atoms try to have a filled shell of 8 valence electrons. • Finally, you just learned that it is the valence electrons which are involved in chemical bonds. • So, you can put the above together and start to draw structures of atoms, ions, and molecules using the valence electrons. • These structures are called Lewis Structures after the chemist who developed them. • In Lewis Structures, the valence electrons are placed around the atomic symbol of the atom, up to 2 per side, for a mazimum of 8! We use a dot to show an electron. • Ex: Draw the Lewis Structure for C. • Carbon has 4 valence electrons (count across), so we would place 1 electron (or dot) on each side: • You can also draw Lewis Structures for ions: Draw the Lewis Structure for F - . •F - has 8 valence electrons, so we would place 2 electrons on each side. • We put F - in square brackets as it has a negative charge. This shows that the negative charge is spread over the entire atom. • A neutral atom of F has 7 valence electrons and an electron configuration of 1s 2 2s 2 2p 5 , so by gaining one electron, F - has achieved an octet of valence electrons and a noble gas configuration as Ne: 1s 2 2s 2 2p 6 • Your Turn: Draw the Lewis Structure for P. C [ F ] -
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Now it’s time to learn to draw Lewis Structures for molecules where electrons are shared! • For example, the H 2 and Cl 2 molecules have covalent bonds with electrons being shared. • By drawing the Lewis Structures for the atoms, you can then see how these atoms would share electrons. • Remember, the shared electrons form the covalent bond. Note in the figures below, that we replace the 2 shared electrons with a single line to represent the covalent bond. • But these are easy molecules with only 2 atoms. How do you draw Lewis Structures for more complicated molecules? • Of course, there are rules or guidelines to follow! 1) Sum the valence electrons from all of the atoms in the molecule. (Don’t worry about which valence electrons came from which atom, remember they are going to share!) 2) Write the atomic symbols for the atoms showing which atoms are connected to each other by connecting them with a single line. This represents 2 shared electrons or a covalent bond.
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This note was uploaded on 06/25/2008 for the course CHEM 400-401 taught by Professor Dr.samples during the Fall '06 term at American River.

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Ch400Ch7LN2 - Lewis Structures(Lewis Dot Structures or Electron Dot Structures You learned how to write electron configurations and Noble Gas

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