What is Lewis Structure or Lewis dot structure?
Lewis structure or Lewis dot structure is an indicative diagram of chemical bonding. It provides a picture of bonding in molecule and ions in terms of a shared pair of electrons and the octet rule. This diagram provides the following information:
- The bonding atoms.
- The no. of a bond formed between the atoms. (single, double or triple bond)
- The no. of the lone pair left in an atom.
Thus the Lewis structure makes it easy to study the compounds.
Rules to follow to draw Lewis dot structure
The Lewis structure can be written by using the following rules:
- First of all, calculate the total no. of valence electrons present in the molecule so as to bond them together to attain the nearest noble gas configuration. This no. can be obtained by adding the valence electrons of the combining atoms.
For example, in the NH3 molecule, there are eight valence electrons available for bonding (5 from Nitrogen and 3 from the three hydrogen atoms).
- For anions, each negative charge would result in the addition of one electron. For cations, each positive charge would mean subtraction of one electron from the total number of valence electrons.
For example, in the SO42- ion, the two negative charges indicate the excess of two electrons than those provided by the neutral atoms.
For Ca2+ ion, two positive charges indicate the deficiency of two electrons from the group of neutral atoms.
- The least electronegative element occupies the central position in the molecule or ion.
- The number of electrons are distributed in the molecule in accordance with no. of valence electron present and no. of electron needed to complete octet in the following way:
|Element/Groups||No. of valence electron||No. of lone pair after bonding||No. of bond require to be formed to complete octet|
|7||3||1 (Only single bond can be formed)|
|6||2||2 (single or double bond)|
|5||1||3 (single or double or both)|
|Group 14||4||0||4(single or double or both)|
- First, the single bonds are drawn between the molecules and even after that, if the octet is not complete then the multiple bonding is done till the octet is complete and after that, all the remaining electron pair becomes a lone pair.
Lewis Dot Structure Examples: