Lewis Dot Structures

What is Electron Dot Structure?

Electron dot structures or Lewis dot formula can be drawn if the molecular formula of the compound is known. It defines the nature of bond and position of atoms of the molecule which are connected in the molecule. The representation of molecules in Lewis electron dot structure or just a Lewis structure is in honour of the American chemist Gilbert Newton Lewis.

Lewis dot structures also called electron dot structures are diagrams that describe the chemical bonding between atoms in a molecule. They also display the total number of lone pairs present in each of the atoms that constitute the molecule. Lewis dot structures are commonly referred to as electron dot structures or Lewis structures. Lewis defined a base as an electron pair donor and an acid as an electron pair acceptor.

How to Draw Electron Dot Structures?

A Lewis Electron Dot Formula comprises of one dot for every valence electron and an element’s symbol. Stages to articulate the electron dot formula are stated beneath. Note down a skeletal structure displaying a realistic bonding pattern by means of only the element symbols.

Pick up every valence electrons from every atom and toss them into a make-believe container that we can term an electron pot.

Make use of the N – A = S equation to get to know the number of bonds

  • The sum of the number of valence electrons is equal to N
  • The number of the valence electron in electron pot is A.
  • The number of electrons shared in the molecule equals S
  • Distribute the electrons from electron pot to account for the bonds
  • Distribute the rest of the electrons

How to Draw Lewis Structures?

A 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 steps that must be followed while drawing a Lewis structure are listed below.

  • First, the total number of valence electrons present in the molecule is calculated by adding the individual valencies of each atom.
  • If the molecule is an anion, extra electrons (number of electrons added = the magnitude of negative charge) are added to the Lewis dot structure.
  • When cationic molecules are considered, electrons are subtracted from the total count in order to make up for the positive charge.
  • The least electronegative atom is made the central atom of the molecule or ion.
  • The atoms are now connected via single bonds.
  • Now, the lone pairs of electrons are assigned to each atom belonging to the molecule. Commonly, the lone pairs are assigned to the most electronegative atoms first.
  • Once the lone pairs are assigned, if every atom does not have an octet configuration, a double or triple bond must be drawn to satisfy the octet valency of each atom.
  • If required, a lone pair can be converted into a bond pair in order to satisfy the octet rule for two atoms.

It is important to note that only the valence electrons are considered while drawing Lewis dot structures and the electrons that do not belong to the outermost shell are ignored.

Lewis Structure Examples

The Lewis electron dot structures of a few molecules are illustrated in this subsection.

1. Lewis Structure of CO2

  • The central atom of this molecule is carbon.
  • Oxygen contains 6 valence electrons which form 2 lone pairs. Since it is bonded to only one carbon atom, it must form a double bond.
  • Carbon contains four valence electrons, resulting in zero lone pairs. Therefore, it is doubly bonded to each oxygen atom.
    Lewis Dot Structure of CO2

    Lewis Dot Structure of CO2

2. Lewis Structure of O2

  • An atom of oxygen contains 6 electrons in the valence shell.
  • Four of the valence electrons exist in lone pairs, implying that the oxygen atom must participate in two single bonds or one double bond in order to attain an octet configuration.
  • Since there are only two oxygen atoms in an O2 molecule, the atoms form a double bond resulting in the following Lewis electron dot structure.
    Lewis Dot Structure of O2

    Lewis Dot Structure of O2

3. Lewis Structure of CO (Carbon Monoxide)

  • A carbon monoxide molecule consists of one carbon atom and one oxygen atom.
  • The carbon atom requires four electrons to obtain octet configuration whereas the oxygen atom requires two.
  • Therefore, the valency is satisfied via the donation of a lone pair of electrons for bonding by the oxygen atom.
  • The resulting Lewis electron dot structure displays a triple bond connecting a carbon and an oxygen atom, each holding a lone pair of electrons.
    Lewis Dot Structure of CO

    Lewis Dot Structure of CO

Solved Examples

Problem-1: In terms of electron dot formulas, define the electron structure of the carbonate ion CO32-.

Solution:

One potential electron dot formula for the carbonate ion is

Electron_Dot_Formula

Since all carbon-oxygen bonds are likely to be equal, the electron structure in resonance terms is shown below.

Over the region of all three carbon-oxygen bonds, one electron pair is delocalized.

Problem-2: Cyclopentane – What will be the formula and electron dot structure of this element?

Solution:

Single bonds connect five carbon atoms of cyclopentane in a cyclic form. The molecular formula of cyclopentane is C5H10. The electron dot structure and structural formula of cyclopentane are articulated underneath.

Electron Dot Formula

Thus, the concepts related to Lewis dot structures are discussed briefly in this article along with a few examples. To learn more about this topic and other related topics, register with BYJU’S and download the mobile application on your smartphone.

Practise This Question

How many unbonded electrons are present on N in NO?

Leave a Comment

Your email address will not be published. Required fields are marked *