The following procedure deserve to be provided to build Lewis electron frameworks for more complicated molecules and also ions:

How-to: constructing Lewis electron structures

1. Recognize the total number of valence electron in the molecule or ion.

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add together the valence electron from every atom. (Recall that the number of valence electrons is indicated by the position of the aspect in the periodic table.) If the types is a polyatomic ion, remember to include or subtract the variety of electrons essential to provide the complete charge top top the ion.

For CO32−, because that example, we add two electron to the total since of the −2 charge.

2. Arrange the atom to show details connections.

as soon as there is a central atom, that is typically the the very least electronegative element in the compound. benidormclubdeportivo.orgists usually list this main atom first in the benidormclubdeportivo.orgical formula (as in CCl4 and CO32−, which both have C together the central atom), i beg your pardon is one more clue to the compound’s structure. Hydrogen and the halogens are nearly always connected to only one other atom, therefore they are usually terminal rather than central.

3. Location a bonding pair of electrons in between each pair of nearby atoms to give a solitary bond.

In H2O, because that example, over there is a bonding pair the electrons between oxygen and also each hydrogen.

4. Beginning with the terminal atoms, add enough electrons to every atom to offer each atom one octet (two because that hydrogen).

this electrons will normally be lone pairs.

5. If any kind of electrons space left over, place them top top the central atom.

we will define later that part atoms are able to accommodate much more than eight electrons.

6. If the main atom has fewer electrons than an octet, usage lone pairs from terminal atom to kind multiple (double or triple) bonds come the central atom to attain an octet.

This will certainly not change the number of electrons ~ above the terminal atoms.

7. Last check

always make certain all valence electrons space accounted for and each atom has an octet that electrons other than for hydrogen (with 2 electrons).

The main atom is normally the the very least electronegative aspect in the molecule or ion; hydrogen and also the halogens room usually terminal.

Now let’s apply this procedure come some certain compounds, start with one us have already discussed.

Example (PageIndex1): Water

Write the Lewis framework for H2O.


Steps for creating Lewis Structures

instance (PageIndex1)
1. Recognize the total variety of valence electrons in the molecule or ion.

Each H atom (group 1) has 1 valence electron, and also the O atom (group 16) has actually 6 valence electrons, because that a total of 8 valence electrons.

2. Kinds the atom to show particular connections.


Because H atom are virtually always terminal, the setup within the molecule need to be HOH.

3. Place a bonding pair the electrons between each pair of surrounding atoms to provide a solitary bond.

4. Start with the terminal atoms, include enough electrons to each atom to provide each atom an octet (two for hydrogen).

Placing one bonding pair that electrons in between the O atom and each H atom gives

H -O- H

with 4 electron left over.

Each H atom has a complete valence shell of 2 electrons.

5. If any electrons are left over, location them top top the main atom.

Adding the staying 4 electrons to the oxygen (as two lone pairs) gives the complying with structure:

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since carbon is much less electronegative than oxygen and also hydrogen is usually terminal, C should be the central atom.

3. Ar a bonding pair that electrons between each pair of surrounding atoms to provide a solitary bond.

Placing a bonding pair the electrons in between each pair of external inspection atoms gives the following:


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7. Final check

Both the oxygen and the carbon now have an octet that electrons, therefore this is an agree Lewis electron structure. The O has actually two bonding pairs and also two lone pairs, and also C has four bonding pairs. This is the structure of formaldehyde, i m sorry is provided in embalming fluid.

Exercise (PageIndex1)

Write Lewis electron frameworks for CO2 and also SCl2, a vile-smelling, stormy red liquid the is supplied in the to produce of rubber.

Answer CO2




Answer SCl2




Writing Lewis structures for Polyatomic Ions

Recall that a polyatomic ion is a team of atom that room covalently external inspection together and which carry an overall electrical charge. The ammonium ion, (ceNH_4^+), is created when a hydrogen ion (left( ceH^+ ight)) attaches come the lone pair of one ammonia (left( ceNH_3 ight)) molecule in a coordinate covalent bond.


Exceptions to the Octet Rule

As important and useful together the octet dominance is in benidormclubdeportivo.orgistry bonding, there room some famous violations. This walk not median that the octet dominance is useless—quite the contrary. Similar to many rules, there are exceptions, or violations.

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There room three violations come the octet rule. Odd-electron molecules represent the first violation to the octet rule. Return they room few, some stable compounds have actually an odd variety of electrons in their valence shells. Through an odd number of electrons, at the very least one atom in the molecule will have to violate the octet rule. Examples of stable odd-electron molecules room NO, NO2, and also ClO2. The Lewis electron period diagram because that NO is together follows:


Although the O atom has an octet the electrons, the N atom has actually only seven electrons in the valence shell. Although NO is a secure compound, it is really benidormclubdeportivo.orgically reactive, together are most other odd-electron compounds.

Electron-deficient molecules represent the 2nd violation to the octet rule. These stable compounds have actually less than eight electrons approximately an atom in the molecule. The most typical examples room the covalent link of beryllium and also boron. For example, beryllium can form two covalent bonds, causing only 4 electrons in that valence shell:

how many valence electrons are in one atom of hydrogen