Lewis Dot Structure: Definition, Examples, and Drawing (2024)

Table Of Contents

  • What is Lewis Structure
  • Lewis Structure and Octet Rule
  • How to Draw Lewis Structure
  • Lewis Structures of Covalent Compounds and Ions

What is Lewis Structure

Lewis structure, also known as Lewis dot structure or electron dot structure, is a simple and straightforward way of representing the outermost electron shell in a chemical species like an atom, ion, or molecule. It shows how electrons are positioned around the atoms either as lone pairs or in a chemical bond, typically a covalent bond or a coordinate covalent bond. Dots represent the lone pairs of electrons, and lines represent the bonded electrons. Since an ion has a charge, the charge is placed as a superscript [1-4].

Lewis structure is named after American chemist Gilbert Lewis. In 1916, he introduced valence bond theory, dot structures, and dashed lines to represent chemical bonds.

Lewis Structure and Octet Rule

The octet rule is used to draw the Lewis structure of a compound. This rule applies to the outmost shell of an atom, which is also known as the valence shell. The electrons in the valence shell are known as valence electrons. The number of valence electrons of an element can be determined from the periodic table.

All atoms gain or lose valence electrons to achieve a stable state, i.e., a state with the lowest potential energy. Therefore, atoms tend to have the desired number of electrons in their outermost shell that will enable them to achieve stability. By losing or gaining electrons, atoms take the electronic configuration of their neighboring inert gas atoms. Except for helium, which has 2 electrons, all inert gases have 8 electrons in their outermost shells. This rule that allows atoms to have up to 8 electrons in their valence shell is the octet rule [2-3].

How to Draw Lewis Structure

Parts of a Lewis Structure

A Lewis structure consists of the following parts [4].

1. Element symbol

2. Dots representing the lone pairs

The element symbol, together with the dots, is called the Lewis symbol.

3. Lines indicating chemical bonds – single line for a single or sigma bond, double line for a double bond (one sigma bond and one pi bond), and triple line for a triple bond (one sigma bond and two pi bonds)

4. Brackets around the molecule with a charge placed as a superscript (This point applies only to charged particles)

Lewis Structure of Nitrate Ion (NO3 )

Let us take the example of the covalent compound nitrate ion (NO3) and learn the steps and rules for drawing the Lewis structure of this polyatomic ion [4-9].

Step 1: We start by calculating the total number of valence electrons using the periodic table. First, find this number for each atom of the molecule. Then, add the individual numbers. Finally, to this number, add the electrons coming from the charge of the molecule. The number of valence electrons of the atoms in NO3 is as follows.

Nitrogen (N): 5

Oxygen (O): 6 x 3 = 18

Negative charge (-): 1

Total number of valence electrons: 5 + 18 + 1 = 24

Step 2: Next, we draw the skeleton structure of the molecule by connecting the central atom to other atoms by single lines. The central atom is the one with the maximum number of bonding sites. From step 1, we found that nitrogen has 5 electrons and requires 3 more to complete the octet. On the other hand, oxygen has 6 electrons and requires 2 more. Hence, nitrogen with more bonding possibilities is the central atom.

Step 3: Next, we will determine the number of electrons needed to complete the octet of each atom. Since each chemical bond comprises 2 electrons, 6 of the 24 electrons will occupy the three bonds in the skeleton. The remaining 18 electrons will go to the terminal atoms, which are the oxygen atoms. These non-bonding electrons are lone pairs.

Step 4: Next, we will check if all the octets are filled or not. If they are not, use a lone pair from one of the terminal atoms and form a bonding pair. In this case, one oxygen atom will donate its lone pair to the nitrogen and form a double bond.

Step 5: Next, we calculate the formal charge of each atom. The following formula gives the formal charge.

qf = V – N – B/2

where,

qf: Formal charge

V: Number of valence electrons of the atom

N: Number of non-bonding electrons or lone pairs

B: Total number of electrons shared in bonds with other atoms

Using the formula, the formal charges of nitrogen and oxygen atoms are as follows.

Oxygen

Atoms with single bonds: 6 – 6 – 2/2 = -1

The atom with a double bond: 6 – 4 – 4/2 = 0

Nitrogen

Only nitrogen atom: 5 – 0 – 8/2 = +1

Add all the formal charges to obtain the formal charge of the molecule.

-1 + (-1) + 0 + 1 = -1

Hence, the net charge on the nitrate ion is -1.

Step 6: In step 5, we have seen the Lewis structure of the nitrate ion. However, this is not the simplest form. To show the simplest Lewis structure, draw a bracket around the molecule and indicate the overall charge as a superscript.

The following image summarizes the above steps.

Lewis Structures of Covalent Compounds and Ions

The above image shows the Lewis structures of some common covalent compounds and ions.

Lewis Dot Structure: Definition, Examples, and Drawing (2024)

FAQs

What is an example of a Lewis dot structure? ›

For example, in the first structure of carbon dioxide, each oxygen atom has seven electrons and each carbon atom has six electrons. The final structure has two pairs (two sets of two dots) on each oxygen atom, two oxygen electron dots facing the carbon atom, and two sets of carbon dots (two electrons on each side).

What is the Lewis structure short answer? ›

A Lewis Structure is a very simplified representation of the valence shell electrons in a molecule. It is used to show how the electrons are arranged around individual atoms in a molecule. Electrons are shown as "dots" or for bonding electrons as a line between the two atoms.

What are the 4 steps for drawing Lewis structures? ›

Step 1: Determine the total number of valence electrons. Step 2: Write the skeleton structure of the molecule. Step 3: Use two valence electrons to form each bond in the skeleton structure. Step 4: Try to satisfy the octets of the atoms by distributing the remaining valence electrons as nonbonding electrons.

How to find Lewis symbol? ›

A Lewis Symbol is constructed by placing dots representing electrons in the outer energy around the symbol for the element. For many common elements, the number of dots corresponds to the element's group number. Below are Lewis Symbols for various elements.

What is each dot in a Lewis dot diagram? ›

Lewis electron dot diagrams use dots to represent valence electrons around an atomic symbol. Lewis electron dot diagrams for ions have less (for cations) or more (for anions) dots than the corresponding atom.

What is the Lewis structure in your own words? ›

Answer. Lewis dot structures are simplified drawings of how valence electrons are arranged around atoms in a molecule. They also illustrate bonds between elements in a molecule. Lewis dot structures use the "Octet Rule." The octet rule states that atoms gain, lose, or share electrons on the atom's outer shell.

What is an example of an electron dot diagram? ›

Electron dot diagrams are diagrams in which the valence electrons of an atom are shown as dots distributed around the element's symbol, for example, a beryllium atom with two valence electrons would have two dots around the symbol.

What are the rules for Lewis dot structure? ›

Steps to drawing lewis dot structures:

1) Determine which atoms are connected to each other. 2) Determine the number of valence electrons in the molecule. 3) Place two electrons between each atom in place of the bonds. 4) Add the rest of the available valence electrons to complete the octet of the surrounding atoms.

Why is Lewis structure hard? ›

Lewis dot structures have their limitations: They don't show the relative sizes and lengths of atoms and bonds. They don't show the electron orbitals involved in the bond. They don't show resonance accurately.

Why are Lewis symbols important? ›

Lewis structures (also known as Lewis dot structures or electron dot structures) are diagrams that represent the valence electrons of atoms within a molecule. These Lewis symbols and Lewis structures help visualize the valence electrons of atoms and molecules, whether they exist as lone pairs or within bonds.

What is the basis of Lewis' dot structure? ›

Lewis structures (also known as Lewis dot structures or electron dot structures) are diagrams that represent the valence electrons of atoms within a molecule. These Lewis symbols and Lewis structures help visualize the valence electrons of atoms and molecules, whether they exist as lone pairs or within bonds.

Why do we draw Lewis structures? ›

Lewis diagrams are drawn to examine mechanisms so knowing which parts of a molecule are electron defficient (+) and which are electron rich (-) is vital. It is best to have a formal charge of 0 for as many of the atoms in a structure as possible.

What is an example of an electron dot structure? ›

Each dot in the structure represents one valence electron in the compound. For example, H2 could be drawn as H:H. Each dot represents one valence electron, and the fact that they are placed between the two atoms means that they are being shared bas a covalent bond.

What is the correct Lewis dot structure? ›

Lewis Dot Structure

Lewis structures are a useful way to summarize certain information about bonding and may be thought of as “electron bookkeeping”. In Lewis dot structures each dot represents an electron. A pair of dots between chemical symbols for atoms represents a bond.

What is a Lewis dot atom structure? ›

Lewis structures, also known as Lewis-dot diagrams, show the bonding relationship between atoms of a molecule and the lone pairs of electrons in the molecule. Lewis structures can also be useful in predicting molecular geometry in conjuntion with hybrid orbitals.

References

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