BOND ANGLES & VSEPR
The shapes of various molecules are determined by their bond angles. A bond angle is the angle formed by the imaginary lines that join the nuclei of atoms combined in a molecule. Any two-atom molecule has a bond angle of 180 degrees, which means it is essentially a straight line. A three-atom molecule can have a bond angle of 180 degrees; otherwise, it must have a bond angle that is less than 180 degrees, such as water, which has a bond angle of about 105 degrees. As the bond angle gets smaller and smaller, the atoms of a molecule often become more and more crowded.
Journal # 22
a. If the bond angle in an atom was very small, how might we expect that to affect the stability of the molecule?
Valence-Shell Electron-Pair Repulsion (VSEPR) is a model that helps predict the shape of molecules. The way atoms and nonbonding electrons are attracted and repulsed by one another determines the shape of the molecule. There are many different shapes that simple molecules take on, such as linear, bent, trigonal planar, trigonal pyramidal, tetrahedral, octahedral, and trigonal bipyramidal,
b. Draw Lewis diagrams for methane CH4, and ammona, NH3. Both of these molecules are tetrahedral even though they have a different number of atoms. Why?