In the news: Understanding the molecular structure of compounds has countless applications in our modern lives. Apply molecular orbital theory and interpret molecular orbital diagrams for diatomic molecules and ions.Apply valence bond theory to predict orbital hybridization in atoms, to describe and illustrate sigma and pi bonds in molecules, and to rationalize cis/trans isomerization and/or resonance.Predict molecular polarity and molecular dipole moments by considering molecular shape and bond polarity.Draw and interpret three-dimensional representations of molecules using “dashed” and “wedge” bonds, and estimate bond angles.Predict molecular shape by applying Valence Shell Electron Pair Repulsion Theory (VSEPR).(credit: modification of work by Jefferson Lab) The detailed explanation of bonding described in this chapter allows us to understand this phenomenon. Other diatomic molecules (like N 2) flow past the magnet. However, when we pour liquid oxygen through a magnet, the molecules line up with the magnetic field, and the attraction allows them to stay suspended between the poles of the magnet where the magnetic field is strongest. Oxygen molecules orient randomly most of the time, as shown in the top magnified view. We need to understand the additional concepts of valence bond theory, orbital hybridization, and molecular orbital theory to understand these observations. We can pour liquid nitrogen through a magnetic field with no visible interactions, while liquid oxygen (shown in Figure 1) is attracted to the magnet and floats in the magnetic field. Yet oxygen demonstrates very different magnetic behavior than nitrogen. Both N 2 and O 2 have fairly similar Lewis structures that contain lone pairs of electrons. We know that electrons and magnetic behavior are related through electromagnetic fields. For example, MO Theory correctly explains the observed magnetic behavior of N 2 and O 2. For this reason, we will consider additional theories of bonding in molecules (Valence Bond Theory and Molecular Orbital Theory) as alternatives to Lewis structures and VSEPR theory. You will also learn how Lewis structures, VSEPR, and atomic electron configurations do not adequately explain all experimental observations of molecular geometry. In this module, you will learn about Valence Shell Electron Pair Repulsion Theory (VSEPR) and how it allows us to predict the shapes of molecules. We have examined the basic ideas of bonding, showing that atoms share electrons to form molecules with stable Lewis structures.
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