Question

Predict the geometry of the following species: (a) \(\mathrm{ClF}_{2}^{-}\) (b) \(\mathrm{SeF}_{5} \mathrm{Br}\) (c) \(\mathrm{SO}_{3}^{2-}\) (d) \(\mathrm{BrO}_{2}^{-}\)

Short answer

(a) The molecular geometry of ClF₂⁻ is T-shaped. (b) The molecular geometry of SeF₅Br is octahedral. (c) The molecular geometry of SO₃²⁻ is trigonal planar. (d) The molecular geometry of BrO₂⁻ is bent or V-shaped.

Step-by-step solution

(a) ClF2-: Step 1: Central Atom and Valence Electrons

First, identify the central atom: Cl. Now, count the valence electrons around the central atom. Chlorine has 7 valence electrons, and there are two bonds to fluoride atoms (7x2 = 14), plus one extra electron from the negative charge, for a total of 22 valence electrons.

(a) ClF2-: Step 2: Electron Pairs Around Central Atom

Next, divide the total number of valence electrons by 2, giving the number of electron pairs. This results in 11 electron pairs around the central atom.

(a) ClF2-: Step 3: Determine Geometry

With 11 electron pairs around the central atom (2 bonding pairs and 9 lone pairs), the least repelling geometry is T-shaped. Thus, the geometry of ClF2- is T-shaped.

(b) SeF5Br: Step 1: Central Atom and Valence Electrons

First, identify the central atom: Se. Now, count the valence electrons around the central atom. Selenium has 6 valence electrons, and there are five bonds to fluorine atoms (7x5 = 35) plus one bond to a bromine atom (7), for a total of 48 valence electrons.

(b) SeF5Br: Step 2: Electron Pairs Around Central Atom

Next, divide the total number of valence electrons by 2, giving the number of electron pairs. This results in 24 electron pairs around the central atom.

(b) SeF5Br: Step 3: Determine Geometry

With 24 electron pairs around the central atom (6 bonding pairs and 18 lone pairs), the least repelling geometry is octahedral. Thus, the geometry of SeF5Br is octahedral.

(c) SO3^2-: Step 1: Central Atom and Valence Electrons

First, identify the central atom: S. Now, count the valence electrons around the central atom. Sulfur has 6 valence electrons, and there are three double bonds to oxygen atoms (6x3 = 18), plus two extra electrons from the negative charge, for a total of 26 valence electrons.

(c) SO3^2-: Step 2: Electron Pairs Around Central Atom

Next, divide the total number of valence electrons by 2, giving the number of electron pairs. This results in 13 electron pairs around the central atom.

(c) SO3^2-: Step 3: Determine Geometry

With 13 electron pairs around the central atom (3 bonding pairs and 10 lone pairs), the least repelling geometry is trigonal planar. Thus, the geometry of SO3^2- is trigonal planar.

(d) BrO2-: Step 1: Central Atom and Valence Electrons

First, identify the central atom: Br. Now, count the valence electrons around the central atom. Bromine has 7 valence electrons, and there are two double bonds to oxygen atoms (6x2 = 12), plus one extra electron from the negative charge, for a total of 20 valence electrons.

(d) BrO2-: Step 2: Electron Pairs Around Central Atom

Next, divide the total number of valence electrons by 2, giving the number of electron pairs. This results in 10 electron pairs around the central atom.

(d) BrO2-: Step 3: Determine Geometry

With 10 electron pairs around the central atom (2 bonding pairs and 8 lone pairs), the least repelling geometry is bent or V-shaped. Thus, the geometry of BrO2- is bent or V-shaped.