The Lewis Dot Structure Of Nitrogen Trifluoride

By looking at the Lewis Dot structure of Nitrogen Trifluoride we can understand how it takes on its triangular shape, as seen to the right. It also explains why the molecule is not drawn as a flat triangular shape.

To build a picture of Nitrogen Trifluoride, we need to start with the electron dot diagrams for the elements involved in the molecule. In this case those are Nitrogen and Fluorine. There are many ways to fit Nitrogen and Fluorine together in theory so we use the chemical formula to tell us the number of each type of atom involved. In this case the formula for Nitrogen Trifluoride is NF3, meaning there is one Nitrogen atom and three Fluorine atoms in each NF3 molecule, as seen below.

Once we have the electron dot diagrams for these elements, it is then a simple matter of putting the puzzle together. We need to fit the four atoms into a single molecule and have no gaps left over. This means that when we look at each atom in the finished molecule it must have eight electrons surrounding it, regardless of how many other atoms it is sharing them with.

Each Fluorine atom has only one gap in its outer shell, so it can bond in only one place. Nitrogen has three gaps in its outer shell so it makes sense to place the Nitrogen in the middle of the molecule and attach the Fluorine atoms to it. Note that the eight electrons in the outer shell can be moved around to suit the build of the molecule, though they must be evenly spread across the four quarters of the atom as outlined in the electron dot structure page. Building NF3 looks like this:

When drawing molecules, it is traditional to replace each pair of electrons with a single solid line joining the atoms together. In the case of the electron pairs that do not join to another atom, the line just stops in space. These are called lone pairs. They are often left out of Lewis Dot Structure drawings, as shown below, but they do have an effect on the structure of the molecule.

The electron pairs, which are shown as lines, all have negative charges. This means they push away from each other which is the basis of the VSEPR rules. Doing this gives us the three dimensional picture of Nitrogen Trifluoride without lone pairs, as shown below (image courtesy of Wikimedia Commons):