40 likes | 130 Views
Notes 12.4 Chemistry. Molecular Structure Linear, bent Trigonal planar, trigonal pyramidal tetrahedral. The VSEPR Model. The structure around a given atom is determined by minimizing repulsions between electron pairs.
E N D
Notes 12.4 Chemistry • Molecular Structure • Linear, bent • Trigonal planar, trigonal pyramidal • tetrahedral
The VSEPR Model • The structure around a given atom is determined by minimizing repulsions between electron pairs. • Whenever two pairs of electrons are present around an atom, they should always be placed at an angle of 180 degrees to each other to give a linear arrangement • Whenever three pairs of electrons are present around an atom, they should always be placed at the corners of a triangle (in a plane at an angle of 120 degrees to each other). • Whenever four pairs of electrons are present around an atom, they should always be placed at the corners of a tetrahedron (the tetrahedral arrangement).
Steps for Predicting Molecular Structure Using the VSEPR Model • Draw the Lewis Structure for the molecule • count the electron pairs and arrange them in a way that minimizes repulsions ( that is, put the pairs as far apart as possible). • Determine the positions of the atoms from the way the electron pairs are shared. • Determine the name of the molecular structure from the positions of the atoms. • Molecules with Double Bonds • When using the VSEPR model to predict the molecular geometry of a molecule, a double bond is counted the same as a single electron pair.
Examples Draw VSEPR for the following examples: CO2 H2O SO3 (BF3) NH3 CH4