Learning Objective

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

Ketzbook demonstrates how to draw Lewis diagrams for elements and simple molecules using an easy to follow step-by-step explanation with several examples.Lew. Lewis structure calculator, Drawing Lewis Structures (2).Step 2:Draw a reasonable skeletal structure, using single bonds to join all the atoms.Try to arrange the atoms to yield the most typical number of bonds for each atom.Apply the following guidelines in deciding what element belongs in the center of your structure.

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 simply

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

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

By putting the two electrons together on the same side, we emphasize the fact that these two electrons are both in the 1s subshell; this is the common convention we will adopt, although there will be exceptions later. 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:

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

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:

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:

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

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.

Fluorine and neon have seven and eight dots, respectively:

With 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 1

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:

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:

Test Yourself

What is the Lewis electron dot diagram for each element?

1. phosphorus
2. argon

Answer

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

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:

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:

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.

In making cations, electrons are first lost from the highest numbered shell, not necessarily the last subshell filled. For example, in going from the neutral Fe atom to the Fe²⁺ ion, the Fe atom loses its two 4s electrons first, not its 3d electrons, despite the fact that the 3d subshell is the last subshell being filled. Thus we have

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

Example 2

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⁺.

   Ca²⁺

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

Test Yourself

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

Answer

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?

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

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⁻

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.

a)

b)

7.

a)

b)

9.

a) Mg²⁺

b)

11.

a) Fe²⁺

b)

Molecular Structure Calculations

Colby Chemistry, Paul J. Schupf Computational Chemistry Lab

The simple theories of bonding that we learn in General Chemistry are powerfuland useful. These theories, which include Lewis structures, VSEPR, andhybridization, are simple models that help predict chemicalproperties. However, Lewis dot structures and hybridization are approximationsthat may or may not match reality. We should verify the usefulness of oursimple predictions with molecular orbital theory. If thetheoretical calculations are done carefully, we can learn a lot about chemical structure by comparing our Lewis structures and hybridizationarguments with the molecular orbitals.

The calculations in this database includebond lengths, angles, atomic charges, the dipole moment,bond orders, and molecular orbital energies. The best Lewis structure thatfits the molecular orbitals is also calculated, so you can directlycompare with your predictions. This best Lewis structure is presented withformal electron pair localized bonds and the hybridization of the atomicorbitals used to form these localized bonds. The Chime plugin is neededto see the 3-D structure of the molecules in these pages. See thelink at the bottom of the page for the Chime plugin.

Molecular orbital theory is based on approximations also. These calculationsare done with some of the best available calculation methods (DFT forgeometry and molecular orbital energies and ab initio for properties).We use Alain St-Amant's DeFT program (University of Ottawa).

The Molecular Structure Input Form, see below, will allow you to do calculationsfor molecules not in the database.These calculations take time; 1-2 hours in some cases.

You can use the Formula Search page or browse the links below. As of 07/12/05 there are 1056structures in the database.
A Best Lewis Structure and Donor Acceptor Interactions Tutorialis available to help you interpret those output sections. These Lewisstructure calculations are done using NBO Analysis.
Answer some Study Questions to help your understanding of some interesting chemistry.

Example Molecular Orbital Results

LiHLiFLiClLiOHLiCNLiBrC₂N₂NOO₂COF₂

Many More Diatomic molecules and ions

H₃⁺Li₂OBeH₂BeCl₂diboraneBH₃BH₂CNBH₂SH
BF₃BF₃2-BF₄⁺BF₂O^-BCl₃BH₃NH₃BH₃COBH₃PH₃BO₂NO
C₃C₅H₂OH₃O⁺H₄O⁺O₃O₄CO₂OCScyclic CO₂CO₂^-HCO⁺HOC⁺
N₃ radicalN₃ quartetHN₃N₃^-NCOHNCNHCNNO
NO₂NO₂⁺NO₂^-HOONNOO^-NO₂^- triplet NO₂²⁺NO₃^-NO₃^-triplet NO₂O^-
N₂Ocyclic N₂Ocyclic N₂O₂N₂O₄NO₂NO
ONOOHN₂H₂N₂H₂ tripletH₂NNH₂NN tripletNH₂FNHF₂NF₃NF₄^-N₂F₂N₂F₄BNHF
HNCl⁺NH₂ClN₃ClNCl₂NCl₃NOClONClNClOClNO₂ClNOOt-ClONOOCl₂
OF₂FOO•FOOFFNO₂FOONF₃^-Cl₃^-Cl₃FClF₂⁺
AlH₃AlF₃AlCl₃Al₂Cl₆
SiH₄SiH₃SiH₃SiO₂
P₂PCl₃SO₂SO₃SO₃^-SOCl₂SO₂Cl₂ClO₂ClOOClO₂⁺ClO₂^-ClOO^-
FClOFClO₂K₂O

Many More Binary Hydrides and their Anions, Cations, and Radicals
Many More Triatomic molecules and their Anions, Cations, and Radicals
Many More Period 3 Compounds, Al, Si, P, S, and Cl
Many More Period 4 Compounds, Ga, Ge, As, Se, and Br

Acids

Onium Ions:NH₄⁺NH₃F⁺NH₃Cl⁺H₃O⁺H₃O₂⁺H₂F⁺PH₄⁺H₃S⁺H₂Cl⁺H₂CN⁺
Hydrides:HFHClHCNHCN tripletHNCHNCOHOCNHONCHCNOHNCSHSCNHN₃
H₂N₂H₂N=NN₂H₄H₂O₂P₂H₄H₂SH₂S₂
Oxyacids:H₂CO₃HONHNOHNO₂HNO

Lewis Dot Structure Generator

₃H₂O₂HOFHOCl
HClO₃HClO₄H₃PO₂H₃PO₃H₃PO₄HSOHH₂SO₃H₂SO₄

Anions

Hydride Conjugates:F^-Cl^-OH^-CN^-NCO^-CNO^-NCS^-CNS^-NSC^-N₃^-HN₂^-N₂H₃^-HOO^-
P₂H₃^-HS^-
Oxyanions:HCO₃^-CO₃^2-CO₃OH^-CO₃O^2-NO^-NO₂^-NO₃^-HO₂^-O₂^2-OF^-OCl^-ClO₂^-
ClO₃^-ClO₄^-H₂PO₂^-H₂PO₃^-H₂PO₄^-HPO₄^2-PO₄^3-HOS^-HSO^-
HSO₃^-SO₃^2-HSO₄^-SO₄^2-S₂O₃^2-

Many MoreHydroxyl Compounds, Donor-Acceptor Oxides, Oxyacids, and Anions
Many MoreFormally Double Bonded Hydroxyl Compounds, Donor-Acceptor Oxides, and Oxyacids (e.g.Carbonic and Nitric acid)

Organics

ethaneethyleneacetyleneH₂C=C, vinylidene
methanolformaldehydeformic acidmethylamineCF₃Cl

Many More Carbon Compounds, Organics, and Organic Reagents
Many MoreOrganic Radical Cations, Neutral Radicals, Cations, and Anions

Oxides

NH₃->OCH₃NH₂->OCH₂NH->OCH₃OH->OCH₂O->OCH₂O->O tripletH₂N₂->O
PH₃->OCH₃PH₂->OH₂S->OCH₃SH->OCH₃F->OCH₃OFCH₃Cl->OH₂S->O₂

Reactive Intermediates

OH radicalHOO radicalH₂O₂⁺ radicalHCO₃ radicalCO₃^- radical CO₃OH^-CO₃O^2-peroxodicarbonate dianion, O₂COOCO₂^2-
methylene singlet (CH₂)methylene triplet (CH₂)methyl radical (CH₃)CH₃⁺
ethyl radical (CH₃CH₂)CH₃CH₂⁺ethylene tripletcyclopropane radicalHCC•HCC^-
CH₃NH^-CH₃OH⁺CH₃OH₂⁺CH₃O^-CH₃O radicalCH₂OH⁺CH₃CO⁺CH₂CHO^-
CF₂ singletCF₂ tripletCF₃•CF₃⁺CCl₂ singletCCl₂ triplet

Lewis Dot Structure Calculator Wolfram Worksheet

CHCl singletCHCl tripletCHBr singletCHBr triplet
H₂CF⁺CH₂Cl⁺CH₂Cl^-trans-C₂H₄Cl₂⁺Cl₂C=C singlet
allyl⁺allyl radicalallyl^-allylalcoholradicalallylchloride radical1-chloropropane radical
HCONH^-N₃ radicalN₃³⁺ singlet N₃³⁺ triplet N₂H⁺

Hydrogen Bonded and Neutral Complexes

H₂O dimerNH₃ dimerHF...waterHF...NH₃HCl...NH₃H₂O...H₂SH₂S...H₂OSO₂...H₂OH₂O...formaldehyde
HCN...formaldehydeHCN...H₂CCwater...COwater...HPO₂CO₂...H₂CO₂...CO₂
CO₂...waterH₂O...SO₃H₂S...SO₃PCl₃...Cl₂Cl₂...Cl₂CH₃radical...H₂H₂O...Cl•

Lewis Dot Structure Calculator Wolfram Integral

Ion-Molecule Complexes

Li⁺..H₂OLi⁺..(H₂O)₂BeCl₂²⁺water...superoxide^-
Be²⁺...H₂C=CH₂ unsymmetricalBe²⁺...H₂C=CH₂ symmetricalBe⁺...H₂C=CH₂ unsymmetricalBe⁺...H₂C=CH₂

Lewis Dot Structure Calculator Wolfram Equation

symmetrical
FHF^-CO₂F^-H₂...OH^-water...HCONH^-O₃...Br^-
H₃O⁺...H₂OH₃O⁺...CO₂H₃O⁺...N₂H₃O⁺...HO•NO⁺...H₂ONO⁺

Lewis Dot Structure Calculator Wolfram Algebra

...N₂NO⁺...O₂

Atomic and Ionic Energies

atomic energiescation energiesanion energies

Weird, Wacky, High Energy Structures

HCl^-H₃ClCH₄²⁺COH₂CH₂..HClCH₃OHCH⁺HNCO-cyclicC₄N₂CO₂O^2-CO₂^2-BH₄⁺AlH₄⁺FClPClPF₄⁺F^-ClF₄^-

Go to the

Molecular Structure Input Form

Lewis Dot Structure Calculator Wolfram Calculator

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Results Here

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This work was supported by an Academic Research Infrastructure Grant from the National Science Foundation, no. 9512457.Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Lewis Structure Calculator

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