There are two general approaches to studying bonding in molecules, molecular orbital theory and valence bond theory. The valence bond theory, developed by Linus Pauling among others, can be though of as establishing the geometry of bonds first. For carbon compounds, three hybridizations are discussed: sp3, or tetrahedral hybridization; sp2, or trigonal hybridization; and sp, or digonal hybridization. These lead to bond angles of 109.5°, 120°, and 180°, respectively. A site at Towson state deals with the details of hybridization [local]. More on hybridization with discussion of sigma and pi bonding from Clickamas Community College.
