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 and #6.
Another example for writing Lewis structures following the above procedure is given bellow:
Another example for writing Lewis structures following the above procedure is given bellow:
Let us consider the case of nitrogen dioxide NO2 : NO2 is a red-brown gas with a pungent and irritating odour.
It is one of the most prevalent oxides of nitrogen, NO is the other one. Both are toxic gases with NO2 being a highly reactive oxidant and corrosive. NO2 forms quickly from emissions from cars, power plants and off-road equipment. NO2 can also come from appliances inside homes that burn fuels such as gas, kerosene and wood. In general, the NOx gases are believed to worsen asthmatic conditions and bronchitis, react with the oxygen in the air to produce ground-level ozone, which is also an irritant and eventually form nitric acid when dissolved in water. When dissolved in atmospheric moisture the result is acid rain which can damage trees and crops, entire forest ecosystems, lakes.
It is one of the most prevalent oxides of nitrogen, NO is the other one. Both are toxic gases with NO2 being a highly reactive oxidant and corrosive. NO2 forms quickly from emissions from cars, power plants and off-road equipment. NO2 can also come from appliances inside homes that burn fuels such as gas, kerosene and wood. In general, the NOx gases are believed to worsen asthmatic conditions and bronchitis, react with the oxygen in the air to produce ground-level ozone, which is also an irritant and eventually form nitric acid when dissolved in water. When dissolved in atmospheric moisture the result is acid rain which can damage trees and crops, entire forest ecosystems, lakes.
Step 1: The central atom will be the N atom since it is the less electronegative. Connect the atoms with single bonds:
Step 2: Calculate the # of electrons in π bonds (multiple bonds) using formula (1) in the article entitled “Lewis Structures and the Octet Rule”.
Where n in this case is 3 since NO2 consists of three atoms.
Where V = (5 + 6 + 6 ) = 17
Therefore, P = 6n + 2 – V = 6 * 3 + 2 – 17 = 3 \ there are 2 π electrons in NO2 and a lone electron \ there is a double bond and a lone electron that is not involved in multiple bonding \1 double bond must be added to the structure of Step 1 and a lone electron.
Step 3 & 4: One double bond must therefore be placed to the structure in Step1. Therefore, the Lewis structures for NO2 are as follows:
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Figure 2: Lewis structures for NO2. Odd electron species cannot obey the octet rule on every atom (without dimerizing) but may be treated in the same fashion. The odd electron must be considered as alone electron, not involved in multiple bonding. Placing the lone electron on O would give larger charge separation which is less favorable. |
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