Learning Objectives

  1. Draw a Lewis electron dot diagram for an atom or a monatomic ion.

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 hydrogen is:

image

Because the side is not important, the Lewis electron dot diagram could also be drawn as follows:

image

The electron dot diagram for helium, with two valence electrons, is as follows:

⋅He⋅

The next atom, lithium, has an electron configuration of 1s22s1, so it has only one electron in its valence shell. Its electron dot diagram resembles that of hydrogen, except the symbol for lithium is used:

image

Beryllium has two valence electrons in its 2s shell, so its electron dot diagram is like that of helium:

⋅Be⋅

The next atom is boron. Its valence electron shell is 2s22p1, so it has three valence electrons. The third electron will go on another side of the symbol:

The three dots in the Lewis dot diagram for boron indicates that it. Please help - Brainly.com

Again, it does not matter on which sides of the symbol the electron dots are positioned.

For carbon, there are four valence electrons, two in the 2s subshell and two in the 2p subshell. As usual, we will draw two dots together on one side, to represent the 2s electrons. However, conventionally, we draw the dots for the two p electrons on different sides. As such, the electron dot diagram for carbon is as follows:

What is the difference between a Lewis dot symbol and a Lewis structure? | Socratic

With nitrogen, which has three p electrons, we put a single dot on each of the three remaining sides:

This is a Lewis Dot structure for nitrogen (N). What can you...

For oxygen, which has four p electrons, we now have to start doubling up on the dots on one other side of the symbol. When doubling up electrons, make sure that a side has no more than two electrons.

What is the electron dot diagram for an oxygen atom? | Socratic

Fluorine and neon have seven and eight dots, respectively:

How many dots would be placed around fluorine in a lewis electron dot diagram? (a) 2 (b) 7 (c) 9 (d) 19 | Study.com

Electron Dot Diagrams | Chemistry for Non-MajorsWith the next element, sodium, the process starts over with a single electron because sodium has a single electron in its highest-numbered shell, the n = 3 shell. By going through the periodic table, we see that the Lewis electron dot diagrams of atoms will never have more than eight dots around the atomic symbol.

Example 3.1

Problem

What is the Lewis electron dot diagram for each element?

  1. aluminum
  2. selenium

Solution

  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:

    Lewis dot structures for an atom and Ionic Compounds: Olivia Flashcards | Quizlet

  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:

    \huge \Lewis{0:2.4.6:,Se}

Test Yourself

What is the Lewis electron dot diagram for each element?

  1. phosphorus
  2. argon

Answer

\LARGE \Lewis{0:2.4.6.,P}\hspace{10mm}\Lewis{0:2:4:6:,Ar}

Elements in the same column of the periodic table have similar Lewis electron dot diagrams because they have the same valence shell electron configuration. Thus the electron dot diagrams for the first column of elements are as follows:

image

Monatomic ions are atoms that have either lost (for cations) or gained (for anions) electrons. Electron dot diagrams for ions are the same as for atoms, except that some electrons have been removed for cations, while some electrons have been added for anions. Thus in comparing the electron configurations and electron dot diagrams for the Na atom and the Na+ ion, we note that the Na atom has a single valence electron in its Lewis diagram, while the Na+ ion has lost that one valence electron:

image

Technically, the valence shell of the Na+ ion is now the n = 2 shell, which has eight electrons in it. So why do we not put eight dots around Na+? Conventionally, when we show electron dot diagrams for ions, we show the original valence shell of the atom, which in this case is the n = 3 shell and empty in the Na+ ion.

Anions have extra electrons when compared to the original atom. Here is a comparison of the Cl atom with the Cl ion:

image

Example 3.2

Problem

What is the Lewis electron dot diagram for each ion?

  1. Ca2+
  2. O2−

Solution

  1. Having lost its two original valence electrons, the Lewis electron dot diagram is just Ca2+.
  2. The O2− ion has gained two electrons in its valence shell, so its Lewis electron dot diagram is as follows:
    \large \ce{\Lewis{0:2:4:6:,O}}^{2-}

Test Yourself

The valence electron configuration of gallium, whose symbol is Ga, is 4s23d104p2. What is the Lewis electron dot diagram for the Ga3+ ion? Hint, it will lose electrons in the highest shell first.

Answer

Ga3+

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

Questions

  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?
  5. Draw the Lewis electron dot diagram for each element.
    1. strontium
    2. silicon
  6. Draw the Lewis electron dot diagram for each element.
    1. krypton
    2. sulfur
  7. Draw the Lewis electron dot diagram for each element.
    1. titanium
    2. phosphorus
  8. Draw the Lewis electron dot diagram for each element.
    1. bromine
    2. gallium
  9. Draw the Lewis electron dot diagram for each ion.
    1. Mg2+
    2. S2−
  10. Draw the Lewis electron dot diagram for each ion.
    1. In+
    2. Br
  11. Draw the Lewis electron dot diagram for each ion.
    1. Fe2+
    2. N3−
  12. Draw the Lewis electron dot diagram for each ion.
    1. H+
    2. H

Answers

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

3. The second column of the periodic table.

5.

    1. ⋅Sr⋅

    2. \huge \Lewis{0.2.4.6.,Si}
    1. \LARGE \Lewis{0:,Ti}
    2. \huge \Lewis{0:2.4.6.,P}
    1. \ce{Mg^{2+}}
    2. \LARGE \ce{\Lewis{0:2:4:6:,S}^{2-}}
    1. \ce{Fe}^{2+}
    2. \LARGE \ce{\Lewis{0:2:4:6:,N}^{3-}}

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