In almost all cases, chemical bonds are formed by interaction of valence electron in atoms. Come facilitate our knowledge of exactly how valence electrons interact, a simple method of representing those valence electrons would certainly be useful.

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A Lewis electron period diagramA representation of the valence electrons of an atom that supplies dots about the prize of the element. (or electron period diagram or a Lewis diagram or a Lewis structure) is a representation of the valence electron of an atom that offers dots about the price of the element. The variety of dots equates to the number of valence electron in the atom. This dots are arranged come the right and also left and over and below the symbol, v no an ext than two dots on a side. (It go not matter what order the positions room used.) because that example, the Lewis electron period diagram for hydrogen is simply


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By putting the 2 electrons with each other on the same side, we emphasize the truth that these 2 electrons room both in the 1s subshell; this is the common convention we will certainly adopt, back there will be exceptions later. The following atom, lithium, has actually an electron configuration of 1s22s1, therefore it has only one electron in its valence shell. That is electron period diagram resembles the of hydrogen, except the symbol because that lithium is used:


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Beryllium has actually two valence electron in that is 2s shell, so its electron period diagram is prefer that that helium:


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The next atom is boron. That is valence electron covering is 2s22p1, so it has three valence electrons. The third electron will go on one more side of the symbol:


Again, the does not matter on which political parties of the price the electron dots room positioned.

For carbon, over there are 4 valence electrons, two in the 2s subshell and also two in the 2p subshell. As usual, us will attract two dots together on one side, to represent the 2s electrons. However, conventionally, we draw the dots because that the 2 p electrons on different sides. Together such, the electron period diagram for carbon is together follows:


For oxygen, which has 4 p electrons, us now need to start copy up top top the dots on one various other side of the symbol. Once doubling increase electrons, make sure that a side has no much more than 2 electrons.


With the following element, sodium, the process starts over with a single electron because sodium has a solitary electron in its highest-numbered shell, the n = 3 shell. By going v the routine table, we check out that the Lewis electron dot diagrams of atoms will never ever have much more than eight dots approximately the atom symbol.


Example 1

What is the Lewis electron dot diagram for each element?

aluminum selenium

Solution

The valence electron construction for aluminum is 3s23p1. So it would have three dots about the symbol for aluminum, 2 of them combine to represent the 3s electrons:


The valence electron configuration for selenium is 4s24p4. In the highest-numbered shell, the n = 4 shell, over there are 6 electrons. The electron period diagram is as follows:


For atom with partially filled d or f subshells, these electrons are frequently omitted from Lewis electron dot diagrams. For example, the electron dot diagram because that iron (valence shell configuration 4s23d6) is as follows:


Elements in the same shaft of the routine table have comparable Lewis electron dot diagrams since they have the exact same valence shell electron configuration. For this reason the electron period diagrams for the an initial column of facets are together follows:


Monatomic ions room atoms that have actually either lost (for cations) or gained (for anions) electrons. Electron period diagrams because that ions room the exact same as because that atoms, except that some electrons have been eliminated for cations, while part electrons have been added for anions. For this reason in comparing the electron configurations and electron period diagrams for the Na atom and the Na+ ion, we keep in mind that the Na atom has actually a solitary valence electron in the Lewis diagram, when the Na+ ion has actually lost that one valence electron:


Technically, the valence covering of the Na+ ion is now the n = 2 shell, which has actually eight electron in it. So why do we not put eight dots around Na+? Conventionally, once we display electron dot diagrams because that ions, we display the original valence shell of the atom, i beg your pardon in this case is the n = 3 shell and empty in the Na+ ion.

In make cations, electron are an initial lost indigenous the highest numbered shell, not necessarily the last subshell filled. Because that example, in going from the neutral Fe atom to the Fe2+ ion, the Fe atom loser its 2 4s electron first, not its 3d electrons, regardless of the truth that the 3d subshell is the critical subshell gift filled. For this reason we have


Anions have extra electrons when compared to the initial atom. Right here is a compare of the Cl atom v the Cl− ion:


Example 2

What is the Lewis electron period diagram because that each ion?

Ca2+ O2−

Solution

Having shed its two initial valence electrons, the Lewis electron dot diagram is simply Ca2+.

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Ca2+

The O2− ion has obtained two electrons in its valence shell, for this reason its Lewis electron period diagram is together follows:


Test Yourself

The valence electron configuration of thallium, who symbol is Tl, is 6s25d106p1. What is the Lewis electron period diagram because that the Tl+ ion?

Answer


Key Takeaways

Lewis electron dot diagrams use dots to represent valence electrons roughly an atom symbol. Lewis electron dot diagrams because that ions have actually less (for cations) or an ext (for anions) dots 보다 the corresponding atom.

Explain why the very first two dots in a Lewis electron period diagram are drawn on the very same side the the atomic symbol.


Is it important for the very first dot approximately an atomic symbol to walk on a particular side the the atom symbol?