06 Lewis dot_metal

06 Lewis dot_metal - 42 8. Some More Complex Covalent...

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42 8. Some More Complex Covalent Molecules: SO 2 is sulfur dioxide. There must be some uses for sulfur dioxide, but it is best known as one of the three major contributors to acid rain. The Lewis dot structure of sulfur dioxide is not so simple. You might predict a ring compound because sulfur is isoelectric with oxygen. Sulfur is too big. SO 2 cannot form a ring like ozone. S O O O S O The usual first steps give a “molecule” with 7 e- on each of the oxygens and 8 e- on the sulfur. If we share one more electron from each oxygen with the sulfur (the method we have been using to increase the number of electrons in the valence shell of atoms) the molecule we get has 8 e- on each oxygen, but 10 e- on the sulfur. That cannot be the correct. O S O The arrows indicate the moves I propose for electrons. O S O O S O O S O The oxygens both need to gain 1 electron, but the sulfur has enough electrons. If sulfur gains 1 more electron by sharing with 1 of the oxygens, the sulfur must lose an electron to keep its valance shell just filled. So lets share an electron with 1 of the oxygens and push the other electrons out to the other oxygen. All of the atoms have 8 e-. SO 3 is sulfur trioxide. Sulfur trioxide also contributes to acid rain. S O O O S O O O 7 7 7 9 Our first effort to work out the dot structure has to many electrons on the S and not enough on the O’s. So lets just push an electron from the over loaded S to one of the O’s
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43 S O O O S O O O 8 8 7 7 Now we are back to the same problem we had with SO 2 , S with 8 e- connected to 2 oxygens with 7 e-. We should be able to fix this the same way as SO 2 . S O O O S O O O Obviously I want you to be able to do Lewis Dot Structures. Lewis Dot Structures are useful because they explain a lot of chemistry. With dot structures you can predict if a chemical can exist or not. Examples: Try to make dot structures for NH, NH 2 , NH 3 and N 2 H 4 NH = nitrogen hydride N H N H Do you see the problem? NH 2 = nitrogen dihydride N H H N H H Do you see the problem? NH 3 = ammonia N H H H N H H H All of the atoms have full valence shells so this molecule probable exists. N 2 H 4 = dinitrogen tetrahydride N N H H H H N H N H H H All of the atoms have full valence shells so this molecule probable exists. 9. Naming Covalent Molecules: I’ve named enough chemicals that you may have already figured out the nomenclature for covalent compounds. 1. Give the name of the least electronegative element first. 2. Give the name of the most electronegative element second. ie.; name the elements in a covalent compound as they appear on the periodic table, reading left to right and bottom to top. Said another way, name them in the same order you name ionic compounds. 3.
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This note was uploaded on 09/05/2011 for the course CHEM 105 taught by Professor Bradbammel during the Spring '11 term at Boise State.

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06 Lewis dot_metal - 42 8. Some More Complex Covalent...

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