Simple Procedure for writing Lewis Structures – Lewis Structures for NO2+ and HCN | Chemistry Net

# Simple Procedure for writing Lewis Structures – Lewis Structures for NO2+ and HCN

Simple Procedure for writing Lewis Structures - Lewis Structures for NO2+ and HCN

# Lewis Electron Dot Structures of Hydrogen Cyanide (HCN) and Nitronium Ion (NO2+)

A simple procedure for drawing Lewis dot structures was given in a previous post entitled Lewis Structures and the Octet Rule”.

Several worked examples relevant to this procedure were given in previous posts please see the index page Lewis Structures & the Octet Rule - Theory & Examples . Let us examine the case of nitronium ion NO2+and hydrogen cyanide HCN.

Let us consider the case of NO2+. The Lewis dot structures of NO2+ with formal charges are as follows:

Step 1: The central atom will be the N atom since it is the less electronegative.  Connect the N with the O atoms with single bonds:

Step 2: Calculate the # of electrons in p bonds (pi 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 = (6 + 5 + 6) - 1 = 16   Therefore, P = 6n + 2 - V = 6 * 3 + 2 - 16 = 4

Therefore,there are 4 electrons (pi electrons) in NO2+   and 2 double bonds must be added to the structure of Step 1 or 1 triple bond.

Step 3 & 4: Two double bonds between N and O are added to the structure in step 1. Alternatively, 1 triple bond is added between N and O. Unshared electron pairs are added so that there is an octet of electrons around each atom. All the equivalent resonance structures of NO2+ are drawn by delocalizing electron pairs. Therefore, the Lewis structures for NO2+ are as follows:

Let us consider the case of  hydrogen cyanide, HCN and draw the Lewis structures of HCN molecule:

Step 1: The central atom will be the C atom since it is the less electronegative (H is a terminal atom so it cannot be a central atom). Connect the atoms with single bonds.

Step 2: Calculate the # of electrons in p bonds (pi bonds, multiple bonds) using formula (1) in the article entitled "Lewis Structures and the Octet Rule".

Where n in this case is 2 since HCN consists of three atoms but one of them is a H atom. Where V = (1 + 4 + 5) = 10   Therefore, P = 6n + 2 - V = 6 * 2 + 2 - 10 = 4      Thus, there are 4 pi electrons (pi electrons) in HCN and therefore 2 double bonds must be added to the structure of Step 1 or 1 triple bond.

Step 3 & 4: Since only two electrons can be accommodated by a H atom double bonds cannot be added to the structure of Step 1. Alternatively, 1 triple bond is possible between C and N atoms. Unshared electron pair (lone pair) is added so that there is an octet of electrons around each atom. Therefore, the Lewis structures of HCN molecule are as follows:

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