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 a dipole moment of \(1.24 \mathrm{D}\) and the (a) Determine the magnitude of \(\mathrm{Cl}-\mathrm{O}\) bond length is \(1.60 \mathrm{~A}\). the charges on the \(\mathrm{Cl}\) and \(\mathrm{O}\) atoms in units of the electronic charge, e. (b) Based on the electronegativities of the elements, which atom would you expect to have a negative charge in the ClO molecule? (c) By using formal charges as a guide, propose the dominant Lewis structure for the molecule. Are the formal charges consistent with your answers to parts (a) and (b)? Can you reconcile any differences you find?

Short answer

In summary, we found the magnitude of the charges on the Cl and O atoms in the ClO molecule to be \(+0.61\,e\) and \(-1.61\,e\), respectively, using the dipole moment and bond length. Based on electronegativity values, we expected the O atom to have a negative charge. The dominant Lewis structure is written as \( \overset{\ominus}{O}=Cl\overset{\oplus}{:} \), which gives formal charges of +1 on both atoms. Although there is a discrepancy between the calculated charges and the formal charges, it is due to the assumptions and limitations of each method used for evaluating the electronic distribution within the molecule.

Step-by-step solution

Calculate the charges on Cl and O atoms

First, let's find out the charges on the Cl and O atoms using the dipole moment and bond length values. The formula for the dipole moment is: \[ \mu = q \cdot d \] Where: - \(\mu\) is the dipole moment \(1.24\,D\), - \(q\) is the charge we want to find, and - \(d\) is the bond length of \(1.60 \, \text{\AA} = 1.60 \times 10^{-10}\,m\). Now, let's isolate the charge, q: \( q = \frac{\mu}{d} \) Now plug the values into the formula and calculate q: \( q = \frac{1.24 \, D}{1.60 \times 10^{-10} \, m} \) Since \(1 \, D = 3.336 \times 10^{-30}\,C\cdot m \), we'll convert the dipole moment to Coulomb meters: \( q = \frac{1.24 \times 3.336 \times 10^{-30}\,C\cdot m}{1.60 \times 10^{-10} \, m} \) \( q \approx 2.58 \times 10^{-19} \, C \) To find the charge in units of the electronic charge (e), we need to divide it by the elementary charge (\(1.602 \times 10^{-19} \, C\)): \( q_e = \frac{2.58 \times 10^{-19}\,C}{1.602 \times 10^{-19}\,C} = 1.61\,e \) Now that we have the charge, q, we know that the O atom's charge is greater in magnitude than the Cl atom's charge. The charges on both atoms add up to zero, so the Cl atom has a charge of \(+0.61\,e\) and the O atom has a charge of \(-1.61\,e\).

Identify the atom with negative charge

Next, let's predict which atom has a negative charge based on the electronegativities of the elements. The electronegativity of Cl is approximately \(3.16\), and the electronegativity of O is around \(3.44\). Since oxygen's electronegativity is higher, it indicates that oxygen is more electronegative, meaning it has a stronger ability to attract electrons, so oxygen would be expected to have a negative charge in the ClO molecule.

Determine the dominant Lewis structure and formal charges

Now, let's find out the dominant Lewis structure for ClO and calculate the formal charges. Lewis structure can be represented as: \[ \overset{\ominus}{O}=Cl\overset{\oplus}{:} \] Calculating the formal charge for both atoms: - Cl: \(7 - 6 = +1\) - O: \(6 - 5 = +1\) The formal charges are not consistent with the charges calculated in part (a). The reason for this discrepancy might be due to the fact that the formal charge method assumes equal sharing of electrons in a bond, while the actual situation in the molecule might be different. We can reconcile these differences by understanding that these charge calculations are not always perfect. It's essential to recognize that the formal charge is merely one approach to evaluate the electronic distribution within the molecule, and differences in results might arise due to the limitations of each approach.

Key concepts

Ozone Layer Depletion

Chlorine monoxide (ClO) plays a significant role in the depletion of the ozone layer, which is crucial in protecting life on Earth from harmful ultraviolet (UV) radiation. When chlorine monoxide interacts with ozone (O\(_3\)), it catalyzes the breakdown of ozone molecules. Chlorine atoms released from ClO engage in a series of reactions that consume ozone, perpetuating a cycle that leads to substantial ozone layer thinning. This catalytic process is particularly concerning at high altitudes in the stratosphere.
The presence of ClO and other chlorine-containing compounds is largely attributed to human-made substances like chlorofluorocarbons (CFCs). Once in the stratosphere, these CFCs break down, releasing chlorine atoms. Understanding how ClO contributes to ozone layer depletion underscores the need for regulatory measures, such as the Montreal Protocol, which aims to phase out ozone-depleting substances.

Dipole Moment

The dipole moment of a molecule provides insight into its electrical polarity. In the case of chlorine monoxide ( ClO ), the dipole moment of 1.24 Debye reveals how charges are distributed between the chlorine and oxygen atoms.
A dipole moment occurs because of the uneven sharing of electrons between atoms in a chemical bond. In simple terms, it's a measure of how positive and negative charges are distributed within the molecule. The greater the dipole moment, the more polar the bond. This distribution of charge results in a molecule with a positive end and a negative end, which is essential in understanding molecular interactions, such as how molecules behave in electric fields.
The calculation of the dipole moment involves the charge magnitude and the distance between charges. For ClO , the given dipole moment indicates an asymmetrical electron distribution, showing that oxygen pulls the electrons more strongly than chlorine.

Electronegativity

Electronegativity reflects an atom's ability to attract electrons when forming a bond. In the ClO molecule, oxygen has a higher electronegativity (approximately 3.44) compared to chlorine (around 3.16). This difference suggests that oxygen will attract the bond's shared electron pair more efficiently.
Electronegativity values can help predict the behavior of atoms in a molecule. In the case of ClO , since oxygen is more electronegative, it will likely carry a partial negative charge, while chlorine will have a partial positive charge.
Understanding electronegativity helps in predicting molecular properties like bond type and polarity. It serves as a fundamental concept in determining how molecules interact with one another, which is crucial in fields ranging from chemistry to biochemistry.

Lewis Structure

Lewis structures are a visual representation of the arrangement of atoms and electrons in a molecule, helping us understand the molecule's geometry and electron distribution. For chlorine monoxide ( ClO ), the Lewis structure can be drawn with the oxygen atom forming a double bond with the chlorine atom, showing that oxygen is likely to have a negative charge due to its greater electronegativity.
In determining the dominant Lewis structure, formal charges are crucial. The formal charge calculation involves comparing the number of valence electrons in an isolated atom to those in the bonded structure. The ClO Lewis structure suggests formal charges leading to oxygen having a negative charge and chlorine a positive charge.
It's important to reconcile any differences between calculated charges and formal charges by acknowledging that formal charges are theoretical ideals. These calculations provide an approximate view of electron distribution and do not always reflect real situations due to the inherent limitations of assuming equal electron sharing. This understanding aids in predicting molecular behavior and chemical reactivity.