Chem 112 Exam AID Course Pack

Complex molecules ex cohco2h ch2nch32 sf6 co2 h2so4

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Unformatted text preview: f the periodic table will look the same - when drawing molecules as Lewis structures, electrons shared between atoms (i.e. covalent bonds) may simply be placed in between the atoms – or may be drawn as a dash, which represents two shared electrons - Unshared (pairs of) electrons are called lone pairs (water has two lone pairs) Atoms want to get a complete set of valence electrons. They can do this by reaching either 8 or 0. - (The noble gases already have filled valence shells, which is why they’re so stable). - A notable exception to this rule is hydrogen, which has a filled valence shell when it has two valence electrons. - Group V elements other than nitrogen may be given up to ten valence electrons if necessary - Group VI elements other than oxygen may be given up to twelve valence electrons if necessary The last two points are due to the ability of the d orbitals to take extra electrons. (Nitrogen and oxygen are excluded because they don’t have any electrons at energy level 3 or higher). - the expanded valence table can be used to indicate how many bonds and lone pairs each atom tends to form - do not use the expanded valencies if standard valencies can be used for all atoms Whenever two atoms can both reach a filled valence shell by the transfer or sharing of electrons (shared electrons being included in the valence shells of both atoms), they will do so by forming a bond Producing Lewis Structures - whatever positions fill all your valencies are the ones that you should use - try to draw and fill the valencies of the central atoms first - central atoms will generally make the most bonds - double or triple bonds will also likely be associated with central atoms Ethan Newton & Barry Zhang for SOS Winter 2012 9 - most important: carbons are always central atoms, while hydrogens and halogens are always terminal atoms (halogens may be central in some cases) atoms there are only one of might be more likely to be central atoms (other than halogens) the order in which they are listed in the chemical formula may give you clues (other than hydrogens, central atoms tend to come before terminal atoms) don’t miscount the number of atoms, especially for more complex molecules ex...
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This note was uploaded on 10/02/2012 for the course CHEM 112 taught by Professor Carran during the Winter '08 term at Queens University.

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