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 Conditions for Writing the Lewis Dot Structures

This article contains study material notes on conditions for writing the Lewis dot structures.

If the molecular formula of a molecule is known, electron dot structures or Lewis dot formulas can be drawn. It specifies the type of bond and the relative positions of the molecule’s atoms. In honour of American chemist Gilbert Newton Lewis, molecules are represented in a Lewis electron dot structure, or simply a Lewis structure. Lewis dot structures, also known as electron dot structures, are diagrams that show how atoms in a molecule interact chemically. They also show how many lone pairs there are in each of the molecule’s atoms. Electron dot structures, also known as Lewis structures, are a type of Lewis dot structure. A base is an electron pair donor, whereas an acid is an electron pair acceptor, according to Lewis. For example, Lewis dot symbols are used to represent the formation of a water molecule from two hydrogen atoms and an oxygen atom.

Lewis Dot Structure

The electronic structures of the elements, particularly how electrons are coupled, are reflected in Lewis dot structures. Lewis structures can be thought of as ‘electron book keeping’ because they help to summarise some information regarding bonding. Each dot represents an electron in Lewis dot structures. A bond is represented by a pair of dots between atom chemical symbols.

What are the steps to drawing electron dot structures?

The Lewis Electron Dot Formula consists of one dot for each valence electron, as well as the element’s symbol. The procedures for expressing the electron dot formula are as follows:

  • Use the N − A = S equation to get the number of bonds.
  • The total number of valence electrons is N.
  • There are valence electrons in the electron pot.
  • S is the number of shared electrons in the molecule.
  • Distribute the electrons from the electron pot to account for the bonds.
  • Make a uniform distribution of the remaining electrons.

What is the best way to draw Lewis Structures?

For more complex compounds and ions, use the following approach to construct Lewis electron structures:

  • Arrange the atoms in such a way that specific connections are visible. When there is a central atom in a compound, it is usually the least electronegative element. This central atom is typically mentioned first in the chemical formula (as in CCl4 and CO32-, which both have C as the central atom), giving even another clue to the structure of the molecule. Because hydrogen and the halogens are frequently bound to only one other atom, they are referred to as terminal elements rather than central elements.
  • Calculate the total number of valence electrons in the molecule or ion. Each atom’s valence electrons are combined together. (Remember that the quantity of valence electrons is determined by the element’s location in the periodic table.)
  • If the species is a polyatomic ion, remember to add or subtract the number of electrons required to give the overall charge of the ion. We add two electrons to the total because of the two charges on CO32- because of the -2 charge.
  • Place a bonding pair of electrons between each pair of adjacent atoms to form a single bond. Each hydrogen and oxygen atom in H2O, for example, has a bonding pair of electrons.
  • Starting with the terminal atoms, add enough electrons to each atom to give it an octet (two for hydrogen). These are mainly lone electron pairs. Any remaining electrons should be placed on the centre atom. We’ll talk about how some atoms can hold more later.
  • If the central atom has fewer electrons than an octet, use lone pairs from terminal atoms to form multiple (double or triple) bonds to it. As a result, the number of electrons will remain the same.

For Example

The H2O Molecule

  • H2O is a molecule that is made up of two hydrogen atoms and an oxygen atom. 
  • The order within the molecule must be HOH, because H atoms are almost invariably terminal. 
  • The H atom (group 1) has one valence electron, while the O atom (group 16) has six, for a total of eight valence electrons.
  • H:O:H is formed by sandwiching one bonding pair of electrons between the O atom and each H atom, leaving four electrons free.
  • A full valence shell of two electrons surrounds each H atom.


The Lewis electron dot structure describes the bonding atoms, the number of bonds in the molecule, and the lone pairs left in the bonding atoms. The Lewis dot structure must be written under certain conditions. To do so, sum the valencies of each atom individually to find the total number of valence electrons in the molecule. Extra electrons are added to the Lewis dot structure if the molecule is an anion (amount of electrons added = magnitude of negative charge). To account for the positive charge in cationic compounds, electrons are removed from the overall count. The lone pairs are normally assigned to the most electronegative atoms first. If every atom does not have an octet configuration after the lone pairs have been assigned, a double or triple bond must be drawn to fulfil each atom’s octet valency. If the octet rule for two atoms requires it, a lone pair can be turned into a bond pair. It’s important to remember that while building Lewis dot structures, only valence electrons are taken into account, and electrons from the outermost shell are neglected.


Frequently Asked Questions

Get answers to the most common queries related to the JEE Examination Preparation.

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