Lewis Electron Dot Structures

Lewis Electron dot Structure is a type of representation of valence electrons of atoms and molecules and compounds with their bond structure. Atoms are the tiny particles of an element that are responsible for chemical reactions whereas, molecules are groups of atoms that are chemically bonded together. In this article, we will learn about, Lewis Electron Dot Structures in detail.

What is Lewis Electron Dot Structure?

A Lewis electron dot structure is a way to represent the valence electrons of an atom or molecule using dots placed around the symbol of the element. The dots represent the electrons that are available for chemical bonding. The number of dots in a Lewis structure is equal to the number of valence electrons in the atom or molecule. The arrangement of the dots follows the octet rule, which states that atoms tend to bond in such a way that they have eight valence electrons.

The method of depicting molecules using Lewis electron dot structure, also known as Lewis structure, is named after American chemist Gilbert Newton Lewis. If the chemical formula of a compound is known, it is possible to construct its electron dot structure or Lewis dot formula.

Lewis Dot Structure

A Lewis dot structure is a way to represent the chemical bonding of a molecule or ion. It is named after Gilbert Lewis, who introduced the concept in 1916. In a Lewis dot structure, the chemical symbol of the element is written in the centre, and dots (also called “electron-dot symbols”) are placed around the symbol to represent the valence electrons. The number of dots is equal to the number of valence electrons in the element. The dots are placed around the symbol in pairs and are used to indicate chemical bonds between atoms. These structures are useful for understanding the bonding and reactivity of a molecule.

How to Draw Electron Dot Structure of Elements?

A Lewis Electron Dot Formula is made up of the element’s symbol and one dot for each valence electron. The process of creating the formula involves first writing down a skeletal structure that shows the actual bonding pattern using only the element symbols, and then placing one dot for each valence electron. The steps for doing so are given below,

• Step 1: Write the chemical symbol for the element at the centre of the structure.
• Step 2: Count the total number of valence electrons for all the atoms in the molecule or ion.
• Step 3: Connect the atoms in the molecule or ion using single lines to represent covalent bonds. Each line represents a shared pair of electrons.
• Step 4: Place dots around the chemical symbol of each atom to represent the remaining valence electrons. Each atom should have a complete octet (eight valence electrons) around it, except for hydrogen which only needs two valence electrons.
• Step 5: If the structure has a formal charge, add or remove electrons to balance the charges on the atoms.

Examples of Electron Dot Structures of various compounds are,

Oxygen

For the electron dot structure of oxygen,

• Central atom is oxygen.
• Oxygen contains 6 valence electrons.

 

Nitrogen

For the electron dot structure of oxygen,

• The central atom is nitrogen.
• Nitrogen contains 6 valence electrons.

 

How to Draw Lewis Structure?

A Lewis electron dot structure illustrates the atoms involved in bonding, the number of bonds within the molecule, and the remaining unshared electrons on the bonding atoms.

To draw a Lewis structure, follow these steps:

1. Write the chemical formula for the molecule.
2. Determine the total number of valence electrons in the molecule. This can be done by adding up the number of valence electrons for each atom in the molecule.
3. Draw the skeleton structure of the molecule, with the atoms in their correct arrangement.
4. Place the valence electrons around the atoms. Each atom should have a full octet (8 electrons) in its outermost energy level.
5. Use single bonds to connect the atoms together.
6. If there are not enough electrons to give each atom a full octet, use double or triple bonds or a lone pair of electrons.
7. Make sure that the total number of electrons in the molecule is equal to the total number of valence electrons.
8. Check the Lewis Structure for any formal charge, which can be obtained by (number of valence electrons on free atom) – (nonbonding electrons + 1/2(bonding electrons))
9. If possible, adjust the structure to minimize the formal charge and stabilize the molecule.

We only consider valence electrons in Lewis Structure. Examples of Lewis structure of various compounds are,

Lewis Structure of N₂

• The atom of nitrogen contains 5 electrons in the valence shell.
• 2 of the five electrons exist in lone pairs and implying that nitrogen atom form 1 triple bond or 1 double bond and 1 single bond and 3 single bonds in order to become stable by attaining an octet configuration.
• So we have two nitrogen atoms that form 1 triple bond as shown in the figure to become stable.

 

Lewis structure of CO_2.

• The atom of carbon contains 4 electrons in the valence shell and oxygen contains 6 electrons in the valence shell.
• 4 of the 6 electrons of oxygen exist in lone pairs and implying that both oxygen atoms form 1 one bond with the carbon atom in order to become stable by attaining an octet configuration.
• So we have two oxygen atoms that form 1 double bond each with a carbon atom as the centre atom as shown in the figure to become stable.

 

Lewis Structure of O₂

• The atom of nitrogen contains 6 electrons in the valence shell.
• 4 of the 6 electrons exist in lone pairs and implying that oxygen atoms form 1 double bond and 2 single bonds in order to become stable by attaining an octet configuration.
• So we have two oxygen atoms that form 1 double bond as shown in the figure to become stable.

 

Lewis Structure of CO

• The atom of carbon contains 4 electrons in the valence shell and oxygen contains 6 electrons in the valence shell.
• 4 of the 6 electrons of oxygen exist in lone pairs and implying that oxygen atoms form 1 double bond and 2 single bonds in order to become stable by attaining an octet configuration.
• But this is an exceptional case the Lewis dot structure of the CO is shown in the figure.

 

Solved Examples on Lewis Dot Structure

Example: Draw the electron Lewis structure of water.

Solution:

• The chemical formula of water is H₂O.
• Valence electrons: In water, hydrogen (H) has 1 valence electron and oxygen (O) has 6 valence electrons, for a total of 8 valence electrons.
• Arrange the atoms: Place the oxygen atom in the centre and the two hydrogen atoms surrounding it.
• Create bonds: Using 2 valence electrons, form a single bond between each hydrogen and oxygen atom.
• Complete the octets: To complete the octets, add 6 electrons to the oxygen atom. These electrons can be arranged as 2 pairs of non-bonding electrons.
• Draw the structure: Represent the bonds with lines, and the non-bonding electrons with dots. The final Lewis structure for water would look like

 

Example 3: Draw the electron Lewis structure of CH₂O.

Solution:

• The chemical formula is CH₂O.
• Valence electrons: In CH₂O, hydrogen (H) has 1 valence electron, carbon (C) has 4 valence electrons and oxygen (O) has 6 valence electrons, for a total of 12 valence electrons.
• Arrange the atoms: Place the carbon atom in the centre and the two hydrogen and oxygen atoms surrounding it.
• Create bonds: Using 2 valence electrons of hydrogen, form a single bond between each hydrogen and carbon atom and using 2 valence electrons of oxygen, form a double bond between oxygen and a carbon atom.
• Complete the octets: To complete the octets, add 6 electrons to the oxygen atom. These electrons can be arranged as 2 pairs of non-bonding electrons of carbon. To complete the octets, add 6 electrons to the carbon atom after adding oxygen. These electrons can be arranged as 2 pairs of non-bonding electrons of hydrogen. 
• Draw the structure: Represent the bonds with lines, and the non-bonding electrons with dots. The final Lewis structure for water would look like this.

 

Example 3: Draw the electron Lewis structure of the carbonate ion.

Solution: 

• The chemical formula is CO₃^2-.
• Valence electrons: In CO₃^2-, carbon (C) has 4 valence electrons and 1 oxygen (O) has 6 valence electrons, and 2 oxygen has 2 valence electrons because they got 2 extra elements for a total of 24 valence electrons.
• Arrange the atoms: Place the carbon atom in the centre and the three oxygen atoms surrounding it.
• Create bonds: Using 2 valence electrons of negatively charged oxygen, form a single bond between each oxygen and carbon atom and using 2 valence electrons of oxygen, form a double bond between oxygen and a carbon atom.
• Complete the octets: To complete the octets, add 6 electrons to the oxygen atom. These electrons can be arranged as 2 pairs of non-bonding electrons of carbon. To complete the octets, add 6 electrons to the carbon atom after adding oxygen. These electrons can be arranged as 2 pairs of non-bonding electrons of negatively charged oxygen.. 
• Draw the structure: Represent the bonds with lines, and the non-bonding electrons with dots. The final Lewis structure for water would look like this.

 

Read, More

• Discovery of Electrons
• Proton
• Valence Electrons

FAQs on Lewis Electron Dot Structures

Question 1: What is the octet rule?

Answer:

The octet rule states that atoms tend to attain a stable electron configuration by having 8 valence electrons in their outermost shell.

Question 2: What is a formal charge and how is it calculated in a Lewis structure?

Answer:

Formal charge is an electrical charge assigned to an individual atom within a molecule or ion. It is calculated by subtracting the number of valence electrons of the free atom from the number of electrons assigned to that atom in the Lewis structure.

Question 3: What is the difference between a single bond, double bond and triple bond in a Lewis structure?

Answer:

A single bond represents two electrons shared between two atoms, a double bond represents four electrons shared between two atoms, and a triple bond represents six electrons shared between two atoms.

Question 4: What is a Lewis electron dot structure?

Answer:

A Lewis electron dot structure, also known as a Lewis structure, is a representation of the distribution of electrons in a molecule using dots or crosses around the chemical symbol of each element.

Question 5: How do you represent coordinate covalent bonds in Lewis electron dot structure?

Answer:

Coordinate covalent bonds in Lewis electron dot structure are represented by showing a shared pair of electrons donated by one atom to another.

Question 6: What are the limitations of Lewis electron dot structure?

Answer:

The Lewis electron dot structure has the following limitations:

• It does not show the actual arrangement of electrons in a molecule
• It does not take into account the bonding orbitals and their energies
• It does not consider the delocalized electrons in a molecule
• It does not reflect the correct distribution of electrons in a molecule
• It does not reflect the bond angles and the bond lengths in a molecule.