A Lewis dot structure is a drawing of a molecule. The drawing only “works” f0r stable molecules that actually exist. So it’s a nice tool to explore how atoms bond into more complex substances. A Lewis dot structure is also called a Lewis structure, a Lewis dot diagram, an electron dot structure, or a dot diagram. The Lewis structures are useful for visualization, but do not reveal the bent structure for water (105°), the pyramidal shape for ammonia, or the tetrahedral geometry of the methane molecule. The Lewis diagrams can also help visualize double and triple bonds. Lewis dot structure of Nitride ion. Now let us try Lewis dot structure of Sulfide ion ( S 2-).Two negative charges means sulfur atom has gained two electrons so its electronic configuration is with 18 electrons (instead of 16). Valence electrons are 8 (2 in 3s and 6 in 3p) Lewis dot structure of sulfide ion.

In 1916, ten years before the Schrodinger wave equation, G. N. Lewis suggested that a chemical bond involved sharing of electrons. He described what he called the cubical atom, because a cube has 8 corners, to represent the outer valence shell electrons which can be shared to create a bond. This was his octet rule.

1. Count the number of valence e^- each atom brings into the molecule.For ions, the charge must be taken into account.

   How many valence electrons in BeCl₂?

   How many valence electrons in NO₂^- and NO₂⁺?

2. Put electron pairs about each atom such that there are 8 electrons around each atom (octet rule), with the exception of H, which is only surrounded by 2 electrons. Sometimes it's necessary to form double and triple bonds. Only C, N, O, P and S (rarely Cl) will form multiple bonds.

   Draw the Lewis dot structure for CF₄.

   The number of valence electrons is 4 + 4 ( 7 ) = 32 electrons.

   So, we obtain:

   Draw the Lewis dot structure for CO.

   The number of valence electrons is 4 + 6 = 10 electrons or 5 pairs. Since both C and O allow multiple bonds we can still follow the octet and write:

3. If there is not enough electrons to follow the octet rule, then the least electronegative atom is left short of electrons.

   Draw the Lewis dot structure for BeF₂.

   In BeF₂ number of valence e^- = 2+ 2(7) = 16 e^- or 8 pairs. Since neither Be or F form multiple bonds readily and Be is least electronegative we obtain:

4. If there are too many electrons to follow the octet rule, then the extra electrons are placed on the central atom.

   Draw the Lewis dot structure for SF₄.

   In SF₄ the number of valence electrons is 6 + 4 ( 7 ) = 34 electrons or 17 pairs. Placing the extra electrons on S we obtain:

How can the octet rule be violated in this last example? The octet rule arises because the s and p orbitals can take on up to 8 electrons. However, once we reach the third row of elements in the periodic table we also have d-orbitals, and these orbitals help take the extra electrons. Note that you still need to know how the atoms are connected in a polyatomic molecule before using the Lewis-Dot structure rules.

Homework from Chemisty, The Central Science, 10th Ed.

8.45, 8.47, 8.49, 8.51, 8.53, 8.55, 8.57, 8.59, 8.61, 8.63

Learning Objectives

By the end of this section, you will be able to:

• Write Lewis symbols for neutral atoms and ions

Lewis Symbols of Monoatomic Elements

In almost all cases, chemical bonds are formed by interactions of valence electrons in atoms. To facilitate our understanding of how valence electrons interact, a simple way of representing those valence electrons would be useful.

A Lewis electron dot diagram (or electron dot diagram or a Lewis diagram or a Lewis structure) is a representation of the valence electrons of an atom that uses dots around the symbol of the element. The number of dots equals the number of valence electrons in the atom. These dots are arranged to the right and left and above and below the symbol, with no more than two dots on a side. (It does not matter what order the positions are used.)

For example, the Lewis electron dot diagram for calcium is simply

Figure 1 shows the Lewis symbols for the elements of the third period of the periodic table.

Figure 1. Lewis symbols illustrating the number of valence electrons for each element in the third period of the periodic table.

Lewis symbols can also be used to illustrate the formation of cations from atoms, as shown here for sodium and calcium:Likewise, they can be used to show the formation of anions from atoms, as shown below for chlorine and sulfur:Figure 2 demonstrates the use of Lewis symbols to show the transfer of electrons during the formation of ionic compounds.

Figure 2. Cations are formed when atoms lose electrons, represented by fewer Lewis dots, whereas anions are formed by atoms gaining electrons. The total number of electrons does not change.

Example 1: Writing Lewis DoT SYmbols of Elements

What is the Lewis electron dot diagram for each element?

1. aluminum
2. selenium

Show Answer

1. The valence electron configuration for aluminum is 3s²3p¹. So it would have three dots around the symbol for aluminum, two of them paired to represent the 3s electrons (or three single dots around the atom):

2. The valence electron configuration for selenium is 4s²4p⁴. In the highest-numbered shell, the n = 4 shell, there are six electrons. Its electron dot diagram is as follows:

Check Your Learning

What is the Lewis electron dot diagram for each element?

1. phosphorus
2. argon

Example 2: Writing Lewis DoT SYmbols of Ions

What is the Lewis electron dot diagram for each ion?

1. Ca²⁺
2. O²⁻

Show Answer

1. Having lost its two original valence electrons, the Lewis electron dot diagram is just Ca²⁺.

   Ca²⁺

2. The O²⁻ ion has gained two electrons in its valence shell, so its Lewis electron dot diagram is as follows:

Check Your Learning

The valence electron configuration of thallium, whose symbol is Tl, is 6s²5d¹⁰6p¹. What is the Lewis electron dot diagram for the Tl⁺ ion?

Key Takeaways

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

Exercises

1. Explain why the first two dots in a Lewis electron dot diagram are drawn on the same side of the atomic symbol.

2. Is it necessary for the first dot around an atomic symbol to go on a particular side of the atomic symbol?

3. What column of the periodic table has Lewis electron dot diagrams with two electrons?

4. What column of the periodic table has Lewis electron dot diagrams that have six electrons in them?

Lewis Dot Structure Calculator With Dots

5. Draw the Lewis electron dot diagram for each element.

a) strontium

b) silicon

6. Draw the Lewis electron dot diagram for each element.

a) krypton

b) sulfur

7. Draw the Lewis electron dot diagram for each element.

a) titanium

b) phosphorus

8. Draw the Lewis electron dot diagram for each element.

a) bromine

b) gallium

Lewis Dot Structure Calculator

9. Draw the Lewis electron dot diagram for each ion.

a) Mg²⁺

b) S²⁻

10. Draw the Lewis electron dot diagram for each ion.

a) In⁺

b) Br⁻

11. Draw the Lewis electron dot diagram for each ion.

a) Fe²⁺

b) N³⁻

12. Draw the Lewis electron dot diagram for each ion.

a) H⁺

b) H⁻

Show Select Answer

1. The first two electrons in a valence shell are s electrons, which are paired.

3. The second column of the periodic table

5.

a)

b)

7.

a)

b)

9.

a) Mg²⁺

b)

11.

a) Fe²⁺

b)