Question

The substance chlorine monoxide, \(\mathrm{ClO}(g)\), is important in atmospheric processes that lead to depletion of the ozone layer. The ClO molecule has an experimental dipole moment of \(1.24 \mathrm{D},\) and the \(\mathrm{Cl}-\mathrm{O}\) bond length is \(160 \mathrm{pm} .(\mathbf{a})\) Determine the magnitude of the charges on the \(\mathrm{Cl}\) and \(\mathrm{O}\) atoms in units of the electronic charge, \(e .(\mathbf{b})\) Based on the electronegativities of the elements, which atom would you expect to have a partial negative charge in the ClO molecule? (c) Using formal charges as a guide, propose the dominant Lewis structure for the molecule. (d) The anion ClO \(^{-}\) exists. What is the formal charge on the Cl for the best Lewis structure for \(\mathrm{ClO}^{-} ?\)

Short answer

The charges on Cl and O atoms in the chlorine monoxide (ClO) molecule have a magnitude of 0.16e. Oxygen has a partial negative charge due to its higher electronegativity. The dominant Lewis structure for ClO has a single bond between O and Cl, with Cl having three lone pairs of electrons. The formal charge on Cl in the best Lewis structure for ClO⁻ is -1.

Step-by-step solution

Calculate Charge Magnitude on Cl and O atoms

Given: Dipole moment (P) = 1.24 D Bond length (d) = 160 pm = \(1.60 \cdot 10^{-10} m\) Electric charge (e) = \(1.60 \cdot 10^{-19} C\) Dipole moment (D) is related to the charge and bond length by the formula: D = q * d Where q is the magnitude of the charges on Cl and O atoms, and d is the bond length. We can calculate q as follows: q = \(\frac{D}{d}\) q = \(\frac{1.24D}{1.60 \cdot 10^{-10} m}\) q = \(\frac{1.24 \times 3.34 \times 10^{-30} \mathrm{C}\/{m}}{1.60 \times 10^{-10} \mathrm{m}}\) q = \(2.57 \times 10^{-20}\mathrm{C}\) Now, we have the charge magnitude and need to express it in units of electric charge (e). q = \(2.57 \times 10^{-20} \mathrm{C}\) Magnitude of charges in units of e: q = \(\frac{2.57 \times 10^{-20}\mathrm{C}}{1.60 \times 10^{-19}\mathrm{C}}\) q = 0.16e The magnitude of the charges on Cl and O atoms is 0.16e.

Determine Partial Negative Charge Atom

From the periodic table, the electronegativity values for Cl and O are: Electronegativity of Cl = 3.16 Electronegativity of O = 3.44 Since the electronegativity of oxygen (O) is higher, it will have a partial negative charge in the ClO molecule.

Propose Dominant Lewis Structure

Using formal charges as a guide, we can draw the Lewis structure for ClO as follows: O - Cl ⋅ Oxygen has a single bond to Cl, and Cl has 3 lone electron pairs, as Cl has 7 valence electrons, and one is shared with O to create the bond. Formal charge (FC) = valence electrons - (lone electrons + 1/2(bonded electrons)) Formal charge for Cl = 7 - (6 + 1/2(2)) = 0 Formal charge for O = 6 - (4 + 1/2(2)) = 0 With both formal charges equal to 0, this is the dominant Lewis structure for ClO.

Determine Formal Charge on Cl in ClO⁻

To determine the formal charge on Cl in the ClO⁻ anion, we first draw the Lewis structure: O = Cl ⋅ The extra electron is placed on Cl, making it negatively charged. The bond is now a double bond, and there are 2 lone electron pairs on Cl and O. Formal charge for Cl in ClO⁻ = 7 - (4 + 1/2(4)) = -1 The formal charge on Cl in the best Lewis structure for ClO⁻ is -1.

Key concepts

Dipole Moment

Dipole moment is a measure of the separation of positive and negative charges in a molecule. It is a vector quantity, meaning it has both a magnitude and direction, represented in Debye units (D). In a molecule like chlorine monoxide (ClO), the dipole moment arises due to the difference in electronegativity between chlorine and oxygen atoms.
The dipole moment for ClO is experimentally determined to be 1.24 D, which provides information about the polarity of the molecule. Higher values of dipole moment indicate a greater degree of charge separation. This concept helps in understanding how charges are distributed within the molecule, indicating that one end is slightly negative, and the other is slightly positive.
To calculate the magnitude of the charge separation, you can use the formula \[ q = \frac{D}{d} \] where \( D \) is the dipole moment and \( d \) is the bond length. This helps in quantifying the actual charges that cause the dipole moment.

Lewis Structure

A Lewis structure is a diagrammatic representation of a molecule that shows the bonding between atoms and the arrangement of valence electrons. In drawing a Lewis structure, one must consider how the valence electrons are arranged to satisfy the octet rule for most atoms, which states that atoms tend to share electrons to achieve a stable configuration similar to noble gases.
For chlorine monoxide (ClO), constructing the Lewis structure involves placing Cl and O atoms with their respective valence electrons and forming bonds. Oxygen will typically form a single bond with chlorine. Since each atom wants to have a full outer shell of electrons, any remaining valence electrons become lone pairs around each atom.
The Lewis structure should also minimize formal charges, which is calculated as:\[ \text{Formal charge} = \text{valence electrons} - (\text{lone electrons} + \frac{1}{2}(\text{bonded electrons})) \]This ensures the most stable and accurate representation of the molecule is achieved.

Electronegativity

Electronegativity is a chemical property that describes the tendency of an atom to attract electrons towards itself in a chemical bond. In the periodic table, electronegativity values typically increase from left to right across a period and decrease down a group.
In the ClO molecule, the electronegativity of oxygen (3.44) is higher than that of chlorine (3.16). This difference in electronegativity values means oxygen will have a stronger attraction for the shared electrons in the Cl-O bond. As a result, oxygen carries a partial negative charge, and chlorine a partial positive charge.
Understanding electronegativity helps predict molecular properties such as bond polarity, boiling points, and solubility. This concept is crucial in explaining why the dipole moment is directed towards the more electronegative atom, often affecting the interaction of molecules with each other and their environment.

Ozone Layer Depletion

Ozone layer depletion refers to the thinning of the Earth's ozone layer in the upper atmosphere (stratosphere), which happens due to chemical reactions involving man-made substances. Chlorine monoxide plays a significant role in these processes. When ClO is present in the atmosphere, it reacts with ozone (O3) leading to its breakdown.
This process can be understood through the catalytic cycle:

• ClO reacts with an ozone molecule, releasing chlorine gas and oxygen.
• The released chlorine can continuously react with more ozone, perpetuating the cycle.

This catalytic cycle leads to a reduction in the amount of ozone, which acts as a shield that protects life on Earth from harmful ultraviolet radiation. Understanding the role of ClO in ozone depletion underscores the importance of controlling substances that release chlorine into the atmosphere to protect the ozone layer.