# What is the molecular geometry of a nitrogen molecule, "N"_2 ?

Jan 7, 2016

Linear.

#### Explanation:

In order to be able to determine the molecular geometry of a given compound, you need to first draw its Lewis structure.

Start by calculating how many valence electrons you'd get for a molecule of nitrogen gas, ${\text{N}}_{2}$.

Nitrogen is located in period 2, group 15 of the periodic table, which tells you that it has $5$ valence electrons. This means that the nitrogen molecule will have a total of $10$ valence electrons, $5$ from each of the two nitrogen atoms.

Another important thing to realize about the fact that nitrogen has $5$ valence electrons is that it needs $3$ more to complete its octet.

This tells you that in order for both nitrogen atoms to have a complete octet, each must share three electrons with the other.

Therefore, you must draw a triple bond between the two nitrogen atoms. This will account for $3 \times 2 = 6$ of the molecule's $10$ valence electrons.

The remaining $4$ valence electrons will be distributed as lone pairs, one of each nitrogen atom.

Now, molecular geometry is all about regions of electron density, that is, about how many regions of electron density surround a given atom.

Remember, a region of electron density is

• a single, double, or triple bond - they all count as one region of electron density
• a lone pair of electrons

So, pick one of the two nitrogen atoms and count how many regions of electron density surround it - this is called the steric number.

In this case, one triple bond and one lone pair will amount to two regions of electron density. This means that the atoms have a steric number equal to $2$, which implies that they are $\text{sp}$ hybridized.

According to VSEPR Theory, this molecule falls into the $\text{AX}$ category, i.e. one bond, $\text{A}$, and one lone pair, $\text{X}$.

Therefore, the molecular geometry for this molecule will be linear, with a bond angle of about ${180}^{\circ}$.