We know that molecules are composed of atoms bonded together by the sharing of valence electrons, those being the electrons in the outermost energy level. Because electrons repell each other, the best arrangement of the atoms in the molecule is one that minimizes the repulsions between electrons. This concept is the basis of VSEPR

Let's take a look at a simple example. A pyramid with a three sided base creates a geometry known as trigonal pyramidal. Below is an example with the base shaded.

Side View~Base Shaded	Bottom View~Base Shaded

Next, let's look at the Lewis Electron Dot Structure for nitrogen trifluoride.

Since the Lewis Electron Dot Structure only shows the molecule in one dimension, we have no idea what the geometry is. To see this, we will have to look at the three dimensional model of the molecule. Note that the pairs of electrons, one green and one blue, being shared by nitrogen and fluorine are called bonding pairs and the two blue electrons above nitrogen which are paired but unshared are called non~bonding pairs.

In this model, the electrons being shared by the central nitrogen and the fluorine atoms are represented by the single bonds. The paired but unshared electrons above the nitrogen are not shown.	Adding the paired but unshared electrons from the nitrogen, the non-bonding pair, and also the faces of the pyramid formed by allowing the three fluorine atoms and the non-bonding pair to form the four vertices of the pyramid, the geometry of the nitrogen trifluoride molecule is shown to be trigonal pyramidal.

There is a simple way to predict molecular geometries by counting the numbers of bonding pairs of electrons and the numbers of non~bonding pairs of electron but first we need to look all of the possible geometries.