Question

Challenge The \(\mathrm{ClO}_{4}-\) ion contains numerous lone pairs. Draw its Lewis structure.

Short answer

The Lewis structure of the ClO4- ion contains a central chlorine (Cl) atom surrounded by four oxygen (O) atoms, each bonded through a single bond. The oxygen atoms each have 3 lone pairs (6 electrons), while the central chlorine atom has 4 lone pairs (4 electrons), satisfying the octet rule for all atoms in the structure. The final Lewis structure is: O \ Cl - O / \ O O

Step-by-step solution

Determine the number of valence electrons

First, we need to identify the total number of valence electrons in the ClO4- ion. The valence electrons are the outermost electrons that are involved in bonding. Chlorine (Cl) has 7 valence electrons, and oxygen (O) has 6 valence electrons. Since there are four oxygen atoms and one extra electron from the negative charge, we have: Total valence electrons = 1(7) + 4(6) + 1 = 7 + 24 + 1 = 32 valence electrons

Distribute the electrons

We will now distribute these 32 electrons among the atoms. Start by placing one single bond (two electrons) between the central atom (chlorine) and each of the surrounding oxygen atoms. This uses up 8 electrons (4 single bonds). Next, distribute the remaining 24 electrons (32 - 8 = 24) as lone pairs on the outer (oxygen) atoms. Each oxygen atom will have 3 lone pairs (6 electrons), and this will use all 24 electrons.

Check the octet rule

The octet rule states that each atom should have 8 electrons in its outer shell (except for hydrogen, which should have 2 electrons). In our structure, each oxygen atom has 8 electrons (2 from the single bond and 6 from lone pairs). The central chlorine atom also has 8 electrons (4 from single bonds to oxygen atoms, and 4 from lone pairs).

Draw the Lewis structure

Now that we have determined the number of bonds and lone pairs for each atom, we can draw the Lewis structure of ClO4-. Each oxygen atom will connect to the central chlorine atom with a single bond, and there will be 3 lone pairs on each oxygen atom and 4 lone pairs on the chlorine atom. The final Lewis structure will look like this: O \ Cl - O / \ O O In this structure, each oxygen atom is singly bonded to the central chlorine atom, satisfying the octet rule for all atoms in ClO4-.

Key concepts

ClO4- ion

The ClO4- ion, also known as the perchlorate ion, is a polyatomic ion composed of one chlorine atom and four oxygen atoms. It carries a net negative charge, indicated by the - after its chemical formula. In chemistry, understanding how atoms interact and bond in such ions is essential for comprehending more complex molecules in inorganic chemistry.

When drawing the Lewis structure for the ClO4- ion, chlorine is the central atom. This is typical because it can form a larger number of bonds compared to oxygen. The structure represents both the bonding between atoms and any non-bonding outer electrons, known as lone pairs. As you move forward in studying chemistry, creating such diagrams becomes a valuable tool for visualizing and predicting molecular geometry and reactivity.

Valence electrons

Valence electrons are those electrons in an atom that are found in the outermost electron shell. These electrons play a significant role in chemical bonding since they are the electrons involved in forming bonds. For the ClO4- ion, determining the number of valence electrons is the first step to drawing its Lewis structure.

In the ClO4- ion:

• Chlorine (Cl) has 7 valence electrons.
• Each oxygen (O) atom has 6 valence electrons.
• Adding these values for four oxygen atoms plus an extra electron for the negative charge gives a total of 32 valence electrons.

These electrons are then used to form bonds and create lone pairs in the Lewis structure, providing insights into the molecule’s stability and reactivity.

Octet rule

The octet rule is a principle that atoms tend to bond so that they each have eight electrons in their valence shell, mimicking the electron configuration of a noble gas. This rule applies to most atoms, including those in the ClO4- ion.

In the case of ClO4- :

• Each oxygen atom achieves an octet by forming a single bond with chlorine and possessing three pairs of lone pair electrons. This setup complete its stable eight-electron configuration.
• Chlorine, as the central atom, also obeys this rule, despite having more than eight electrons around it, due to bond expansion. It forms single bonds with each of the four oxygen atoms, accounting for its eight electrons.

Following the octet rule helps us understand how the bonding arrangement satisfies the electron requirements for stability.

Lone pairs

Lone pairs refer to pairs of valence electrons that are not involved in bonding and remain localized on a single atom. In the Lewis structure of the ClO4- ion, lone pairs contribute to the overall electron count influencing both the shape and properties of the ion.

For ClO4- :

• Each oxygen atom has three lone pairs, resulting in six electrons that do not participate in bonding in the Lewis structure. These help complete the octet for the oxygen atom.
• The role of lone pairs is crucial, not only in electron counting but also in predicting the structure’s geometry. They occupy space around the atom, affecting the molecule's three-dimensional shape.

Understanding lone pairs is essential for predicting how the ClO4- ion would interact with other ions and molecules in various chemical environments.