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CHEM 012 7

17 92911 no2 total valence electrons are 17 n is

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Unformatted text preview: pairs. However, this is not correct. Methane is not a flat structure; rather it is 3- dimensional, with 109.5° angles between the electron pairs. This is the farthest the electron pairs can be separated when you have four electron pairs on a single central atom. H H C H H Methane •  •  The actual three dimensional structure of methane is called a tetrahedron because the four H atoms would fit at the corners of a tetrahedron The perfect tetrahedral angle is 109.5° hep://www.elmhurst.edu/~chm/vchembook/204tetrahedral.html 14 9/29/11 Other Structures Based on the Tetrahedron… •  Consider water… Its Lewis structure is H O H Even though there are only two bonded electron pairs, there are sCll a total of four electron pairs surrounding oxygen. Lone pairs actually take up a bit more space than bonded pairs. •  With just three atoms, you might think that water would be a linear molecule. •  It’s NOT; those lone pairs on O play a big role in the structure •  Remember that electron pairs want to be as far apart as they can, which is ~109.5° for four electron pairs around a central atom Water Structure hep://www.elmhurst.edu/~chm/vchembook/206bent.html The extra space required by the lone pairs “pushes” the angle between the bonded pairs so that it is a liele smaller than that of a tetrahedron. 15 9/29/11 Ammonia Structure The Lewis structure for ammonia (NH3) is H N H H Again, there are four electron pairs around the central atom, so the structure will again be based on a tetradral structure Ammonia Agai...
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