A simple procedure for writing Lewis structures is given in a previous article entitled “Lewis Structures and the Octet Rule”. Relevant worked examples were given in the following articles: Examples #1, #2, #3 , #4, #5, #6, #7, #8, #9.
Step 2: Calculate the # of electrons in π bonds (multiple bonds) using formula (1) in the article entitled “Lewis Structures and the Octet Rule”.
Another example for writing Lewis structures following the above procedure is given bellow:
Let us consider the case of nitrous oxide N2O. Nitrous oxide is a colorless and odorless gas that is used as an anesthetic and analgesic in surgery and dentistry. It is also known as “laughing gas” due to the euphoric effects of inhaling it. It is used as an oxidizer in rocketry and in motor racing to increase the power output of engines. Nitrous oxide accounts for about 5% of the greenhouse effect. Although its atmospheric concentration is only 320 ppb, it has 300 times greater ability to absorb infrared radiation than CO2 does. The resonance structures for N2O are as follows:
Step 1: The central atom will be the N atom since it is the less electronegative. Connect the atoms with single bonds:
Where n in this case is 3 since N2O consists of three atoms.
Where V = (5 + 5 + 6 ) = 16
Therefore, P = 6n + 2 – V = 6 * 3 + 2 – 16 = 4 There are 4 π electrons in N2O.
Therefore, 2 double bonds or 1 triple bond must be added to the structure of Step 1.
Step 3 & 4: The Lewis structures for N2O are as follows: