大学化学课件CHAPTER10【荐】.pdf

Chapter 10 : Chemical Bonding II Text sections 10.1 – 10.5 Key Concepts VSEPR theory Predicting molecular geometries Molecular shape and polarity Molecular Geometry •• According to Lewis structure of water H O H you might think the atoms are all in a •• straight line. Lewis structures tell us nothing about the shape of molecules. Experiment shows that this is not the case. Water molecules are bent not linear. •• Molecular geometry is determined by O H •• H the electrostatic repulsions between valence shell e- pairs. But first some terminology… •Bond length : the distances between the nuclei of bonded atoms. •Bond angle : the angles between adjacent lines representing bonds. 97 pm 104.5o VSEPR Theory • e- groups around the central atom will be most stable when they are as far apart as possible; called valence shell electron pair repulsion (VSEPR) theory – since e-s have - charge, they should be most stable when they are separated as much as possible • the resulting geometric arrangement will allow us to predict the shapes and bond angles in the molecule Electron Groups • the Lewis structure predicts the arrangement of valence e-s around the central atom(s) • each lone pair of e-s constitutes one e- group on a central atom • each type of bond (single, double, triple) constitutes one e- group on a central atom •• •• •• there are 3 electron groups on N • O N O • 1 lone pair • • •• 1