Question

Consider the following substances: 1\. OF, 2\. \(\mathrm{Cl}_{2} \mathrm{O}\) 3\. \(\mathrm{Br}_{2} \mathrm{O}\) The correct sequence of \(\mathrm{X}-\mathrm{O}-\mathrm{X}\) bond angle is (a) \(3>2>1\) (b) \(1>2>3\) (c) \(2>1>3\) (d) \(1>3>2\)

Short answer

The sequence is (b) \( 1>2>3 \).

Step-by-step solution

Understand the Basic Structure

The given molecules are dichlorine monoxide (\( \text{Cl}_2\text{O} \)), dibromine monoxide (\( \text{Br}_2\text{O} \)), and oxygen fluoride (OF). We need to examine the structure of \( \text{X-O-X} \) bonds, where 'X' is given by chlorine, bromine, or fluorine.

Analyze Electron Affinity and Electronegativity

Fluorine, chlorine, and bromine have different electronegativities, with fluorine being the most electronegative, followed by chlorine, and then bromine. Higher electronegativity correlates with stronger pull on bonding pairs and a more significant repulsion among lone pairs on X, influencing the bond angle.

Evaluate Bond Angle Relationship

The general trend in the \( \text{X-O-X} \) bond angle is affected by the size and electronegativity of the X atom. Smaller and more electronegative atoms like F will have a larger \( \text{X-O-X} \) bond angle due to greater lone pair repulsion compared to larger atoms with less electronegativity like Br or Cl.

Determine the Sequence of Bond Angles

Comparing the bond angles, we find that due to its size and electronegativity, OF will have the largest angle, followed by \( \text{Cl}_2\text{O} \), and finally \( \text{Br}_2\text{O} \) will have the smallest angle due to its larger size and lower electronegativity.

Key concepts

Electronegativity Effects

Electronegativity is a chemical property that describes an atom's ability to attract and hold on to electrons. Think of it as how strongly an atom pulls on the electrons it shares in a bond with another atom. When comparing fluorine, chlorine, and bromine, fluorine is the most electronegative, followed by chlorine, and finally bromine is the least electronegative. This order plays a crucial role in determining the bond angles in the molecules we are considering.

• Fluorine's high electronegativity means that it has a strong pull on the bonding electron pairs.
• This strong pull not only influences the bond angle by keeping the bonds tighter but also affects the space and repulsion between lone pairs.
• In contrast, bromine, being the least electronegative, exerts a weaker pull on the shared electrons, allowing for looser bond angles.

As electronegativity increases, typically so does the bond angle. In the case of OF, the presence of a strongly electronegative atom like fluorine helps create a larger bond angle compared to when chlorine or bromine is present.

Structure of Molecules

The structure of molecules like OF, \( \text{Cl}_2\text{O} \), and \( \text{Br}_2\text{O} \) is important in understanding their bond angles. These molecules can be understood in terms of basic geometric shapes which are influenced by the types of atoms involved and the electron pairs around the central oxygen atom.

• OF forms linear or bent shapes depending on the lone pairs and bonding electrons.
• The presence of two 'X' atoms, any change in atom type (like \,\text{F}, \,\text{Cl}, \,or \,\text{Br}) will notably affect the structure.
• In \( \text{X-O-X} \) configurations, the position of these atoms creates specific angles that define the molecule's shape.

Understanding the three-dimensional structure is necessary as it governs how electrons and atoms are arranged, which in turn impacts the angle of bonds. Smaller, highly electronegative atoms tend to create larger angles because they pull bonding electrons closer, affecting spatial arrangement around the oxygen atom.

Lone Pair Repulsion

Lone pair repulsion is a key factor in determining bond angles. Lone pairs of electrons occupy more space than bonding pairs because they are not held between two atomic nuclei. This additional space requirement causes repulsion that affects bond angles in a molecule.

• Lone pairs create a push between bonded electron pairs, increasing bond angles between them.
• In molecules like OF, the strong electronegativity of fluorine makes lone pair-bond pair repulsion more pronounced.
• Larger atoms like \( \text{Cl} \) and \( \text{Br} \) have more diffused electron clouds, thus lessening the impact of lone pairs on bond angles.

The repulsion factor becomes crucial when predicting the order of bond angles across molecules with varying sizes and numbers of lone pairs. Ultimately, the more lone pairs, especially when associated with a small and highly electronegative atom, the larger the bond angle due to increased repulsion and electron cloud adjustments.