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Unraveling the Secrets of [ClO3]: Lewis Structures and Molecular Geometry Explained

Lewis Structures and Molecular Geometry: Understanding [ClO3]

Chemistry is a fascinating subject that allows us to understand the world around us at a fundamental level. One of the essential topics in chemistry is the concept of chemical bonding, which describes the interactions between atoms and molecules.

Among the many ways to represent these interactions is the Lewis structure, named after the great American chemist Gilbert Lewis. In this article, we will discuss the Lewis structure and molecular geometry of the chlorate ion ([ClO3]-).

Drawing the Lewis Dot Structure of [ClO3]

The first step in understanding the chlorate ion’s structure is to draw its Lewis structure, also known as the Lewis dot structure. A Lewis structure is a diagram that shows the arrangement of atoms and electrons in a molecule.

It is often used to predict chemical reactivity and molecular properties. To draw the Lewis structure of [ClO3], we need to follow a few key steps:


Valence Electrons Calculation

Before we begin, we need to know how many valence electrons each atom has. Valence electrons are electrons in the outermost shell of an atom that are involved in chemical bonding.

For [ClO3], we have one chlorine atom (Cl) and three oxygen atoms (O). The group number of chlorine and oxygen in the periodic table tells us the number of valence electrons.

For chlorine, group 7A tells us that it has seven valence electrons. For oxygen, group 6A tells us that it has six valence electrons.

There are three oxygen atoms, giving us a total of 3 6 + 7 = 25 valence electrons. 2.

Identifying the Central Atom and Connecting Outer Atoms

The next step is to identify the central atom in the molecule, which is often the least electronegative element. In [ClO3], we have only one central atom, which is Cl. We then connect the outer atoms (O) to the central atom (Cl) with single bonds.

3. Completing the Octet of Outer Atoms and the Central Atom

After connecting the outer atoms, we need to complete the octet of every atom.

An octet is a set of eight electrons. Elements in the second row of the periodic table have four valence orbitals, so they can hold up to eight valence electrons.

To complete the octet of the oxygen atoms, we add three pairs of nonbonding electrons (lone pairs) to each O atom. The Cl atom already has 7 valence electrons, so it needs only one more electron to complete its octet.

We add one pair of electrons as a lone pair to the chlorine atom. 4.

Checking the Stability of the Lewis Structure Using the Formal Charge Concept

Now that we have drawn the Lewis structure for [ClO3], we need to check its stability using the formal charge concept. The formal charge is a way of calculating the charges on each atom in a molecule by assuming that the electrons are equally shared between atoms in covalent bonds or equally distributed between atoms in nonbonding pairs.

The formal charge of an atom in a molecule is calculated as follows:

Formal Charge = (# of valence electrons) (# of lone pair electrons + # of bonding electrons)

If the formal charge on an atom is zero, the atom is stable. If it is positive or negative, it means that the atom is either deficient or overloaded with electrons, respectively.

For [ClO3], we can calculate the formal charges as:

For Cl: FC = 7 6 (4) = 0

For each of the O atoms: FC = 6 6 (4) = -1

Thus, every oxygen has a formal charge of -1, and the Cl has a formal charge of zero. 5.

Minimizing Formal Charges Via Converting Lone Pairs into Covalent Bonds

To make the structure more stable, we can convert one of the lone pairs from an oxygen atom into a covalent bond with chlorine. This conversion neutralizes the charges on the oxygen atom and improves the overall stability of the molecule.

6. Final, Stable Lewis Structure for the Chlorate Ion [ClO3]

The final Lewis structure of [ClO3]- has one single bond between Cl and one of the O atoms (the one on the left), and two double bonds between the remaining O atoms and the Cl. All the O atoms have a formal charge of -1, and Cl has a formal charge of +1.

Shape and Geometry of [ClO3]

The shape and geometry of a molecule are closely related to its electronic structure. We can predict the shape and geometry of a molecule using the valence shell electron pair repulsion (VSEPR) theory.

This theory states that electrons repel each other and try to get as far away from each other as possible, determining the geometry of the molecule. 1.

Determining the Steric Number and Electron Geometry

The steric number of a molecule is the sum of the number of atoms bonded to the central atom and the number of nonbonding electrons around the central atom. For [ClO3]-, the central atom is Cl, which has one single bond and two double bonds with the three O atoms.

Also, there is a total of six non-bonding electrons (two on each O atom). So the steric number is 4+6=10.

Therefore, the electron geometry of [ClO3]- is tetrahedral. 2.

Using VSEPR theory to Determine the Molecular Geometry

The molecular geometry of [ClO3]- can be determined from the electron geometry, which tells us how the atoms are arranged around the central atom. However, the position of nonbonding electrons also affects the molecular geometry.

To determine the molecular geometry, we ignore the nonbonding electrons and look only at the atoms, arranging them in a symmetrical fashion.

In the case of [ClO3]-, we have one single bond and two double bonds between chlorine and oxygen atoms, making it an AX3 molecule (A = central atom; X = outer atoms).

So the molecular geometry is trigonal planar, as all the oxygen atoms are positioned in the same plane and are 120 apart from each other. 3.

Polar or Non-polar Nature of [ClO3]- Molecule

The polarity of a molecule is determined by its shape and the presence of polar bonds. A polar bond is a bond in which the electrons are not shared equally between the two atoms.

This uneven sharing of electrons results in a partial positive or negative charge on each atom in the bond.

If the molecule has a net dipole moment, it is polar.

If it has no net dipole moment, it is non-polar. The dipole moment is zero in symmetrical molecules, while the dipole moment is nonzero in non-symmetrical molecules.

[ClO3]- has a trigonal planar shape with three O atoms in the same plane, each bonded to Cl by the same type of bond. Suppose we assume that the Cl-O bonds are polar, with the bond polarity directed toward the oxygen atoms.

In that case, the bond dipoles cancel out each other. This results in a molecule with no net dipole moment, making it non-polar.


In this article, we have discussed the Lewis structure and molecular geometry of the chlorate ion ([ClO3]-). We have shown how to draw the Lewis structure of [ClO3]-, starting with valence electrons calculation to checking its stability using formal charge, and converting lone pairs into covalent bonds.

We have also seen how to predict the molecular geometry of [ClO3]- using the VSEPR theory, which led to a trigonal planar shape due to a tetrahedral electron geometry. Finally, we have established that [ClO3]- has no net dipole moment, making it a nonpolar molecule.

Understanding the structure and geometry of molecules such as [ClO3]- is crucial for predicting their chemical properties and, by extension, their behavior in chemical reactions. In the previous section, we discussed the Lewis structure and molecular geometry of the chlorate ion ([ClO3]-).

However, sometimes, not all atoms in a molecule or ion can obey the octet rule and still maintain stability. This situation leads to the concept of expanded octets, which defies the traditional eight-electron rule for the second-row elements.

In this section, we will explore the concept of expanded octets and its implications in chemical structures, along with the concept of resonance structures and how they are utilized to explain the unique electronic nature of [ClO3]-.

Explanation of Expanded Octet and Its Implications

The octet rule states that atoms of main-group elements prefer to have eight electrons in their valence shell to obtain stability. This shell closure is exhibited by the inert noble gas elements.

With the exception of H, Li, Be, and B, all second-row elements adhere to this rule for most situations. However, there are examples where atoms such as phosphorus (P), sulfur (S), and chlorine (Cl) can exceed the octet rule and still maintain stability.

The atoms are said to have an expanded octet, where they hold more than eight electrons in their valence shell, often through the utilization of the d orbitals. This phenomenon is observed in third-row elements and below, where the d orbital is accessible for bonding.

For example, the SF6 (sulfur hexafluoride) molecule consists of six covalent bonds between the sulfur atom and fluorine atoms, exceeding the traditional eight-electron rule. The observation of expanded octets has practical implications in chemistry, particularly in the design of new materials and drugs.

For instance, molecules containing phosphorus with an expanded octet have been useful synthetic intermediates in organic chemistry. More generally, the concept of expanded octets expands the periodic table beyond Group 18 to include other elements whose electrons exhibit similar properties.

Understanding the Concept of Resonance Structures

The concept of resonance structures arises when one can draw two or more Lewis structures that differ only in the arrangement of electrons’ positions. These structures are called resonance structures, and they represent the real distribution of electrons in the molecule or ion to a varying degree, hence the name.

In some situations, no single Lewis structure adequately explains all the electronic properties of the molecule, and a combination of these resonance structures needs to be considered. Resonance structures are possible when there are two or more lone pairs or multiple bonds between two atoms in a molecule or ion.

These structures represent possible electronic structures, and the actual structure of the molecule is a hybrid of all the resonance structures. The resonance hybrid is often more accurate than any individual resonance structure in accounting for molecular properties, such as bond length and energy.

Hybrid Structure of the Chlorate Ion [ClO3]

In the Lewis structure of the chlorate ion ([ClO3]-) we drew in the previous section, we counted the valence electrons to be 26. The Lewis structure shows that this ion has one Cl atom bonded to three O atoms with a double bond and two single bonds.

Additionally, each O atom has a single nonbonding electron pair. The formal charge on the Cl atom is zero, while each oxygen atom has a formal charge of -1.

However, a closer look reveals that we can obtain two other, equally valid resonance structures by moving the double bond in Lewis structure 1 to the other two oxygen atoms. In each of these structures, the formal charge on the chlorine atom is +1, while each oxygen atom has a formal charge of 0.

The three possible resonance structures are illustrated below:

Structure 1: Cl=O |O-O|

Structure 2: O=Cl |O-O|

Structure 3: O=O |Cl-O|

The chlorine atom, therefore, has an expanded octet of ten electrons in all three structures. The actual electronic structure of [ClO3] would be the average of the three resonance structures, giving an apparent dipolar, but the charge ion with no net charge, as we showed earlier.

This shows that in certain situations, resonance structures help to explain the shared electron characteristics of a molecule that cannot be explained by a single Lewis structure.


In summary, expanded octets and resonance structures are two important concepts in organic chemistry that help to explain the electronic structure and chemical properties of molecules and ions. Expanded octets help to extend the octet rule beyond the traditional eight-electron rule for second-row elements in molecules, whereas resonance structures offer an explanation of the shared electron nature of molecules with no single Lewis structure.

In the case of the chlorate ion, we were able to show through resonance hybrid that the molecule had no net dipole moment despite having an expanded octet on the Cl atom. Together, these concepts allow chemists to better understand the electronic nature of molecules and ions, aiding better chemical synthesis and property prediction.

In conclusion, the topics of expanded octets and resonance structures are vital in understanding the electronic structure and behavior of molecules and ions. The concept of expanded octets challenges the traditional octet rule and allows for the stability of certain atoms carrying more than eight electrons.

Resonance structures, on the other hand, explain the shared electron nature of molecules through multiple valid Lewis structures. These concepts have practical implications in various fields of chemistry, enabling better comprehension of molecular properties and aiding in the design of new materials and drugs.

By exploring these concepts, we can deepen our understanding of chemical bonding and enhance our ability to predict and manipulate molecular behavior.

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