Draw the structure of Asl3 (arsenic tribromide) for yourself using the steps that we learned in this course. Arsenic is the central atom. Now answer the following questions based on your structure: 1. Arsenic has linear trigonal pyramidal 2. Arsenic has tetrahedral trigonal planar 3. The molecule has bent 4. The molecule has ed pairs connected to it. pair/pairs. electron pair geometry. molecular geometry (shape).
The Correct Answer and Explanation is:
To draw the structure of AsBr₃ (arsenic tribromide), we can follow these steps:
Step-by-Step Approach to Drawing AsBr₃:
- Determine the Lewis Structure:
- Arsenic (As) is the central atom, and it is surrounded by three bromine (Br) atoms.
- Arsenic belongs to group 15, so it has 5 valence electrons. Each bromine atom belongs to group 17, so it has 7 valence electrons.
- The total number of valence electrons is:
5 (As)+3×7 (Br)=26 electrons.5 \, (\text{As}) + 3 \times 7 \, (\text{Br}) = 26 \, \text{electrons}.5(As)+3×7(Br)=26electrons.
- Place bonds between the central atom (As) and the surrounding atoms (Br):
- Each As–Br bond requires 2 electrons, so 3 bonds will use up 3×2=63 \times 2 = 63×2=6 electrons.
- Distribute remaining electrons:
- After the bonds are placed, we have 26−6=2026 – 6 = 2026−6=20 electrons left to be placed as lone pairs. These will be placed on the Br atoms first, as they are more electronegative, and then any remaining electrons will go to the As atom.
- Each Br atom gets 6 electrons (3 lone pairs), and there are no electrons left for the As atom.
- Assess the electron and molecular geometry:
- Arsenic has three bonding pairs and one lone pair on it. This leads to a trigonal pyramidal electron geometry and a molecular geometry that is also trigonal pyramidal.
Answers to the Questions:
- Electron Pair Geometry:
- The electron pair geometry around arsenic is tetrahedral, as there are four regions of electron density (3 bonding pairs and 1 lone pair).
- Molecular Geometry:
- The molecular geometry of AsBr₃ is trigonal pyramidal, due to the three bonding pairs and one lone pair on the arsenic atom. The lone pair of electrons repels the bonding pairs, causing the molecule to have a pyramidal shape.
- Shape of the Molecule:
- The shape of the molecule is trigonal pyramidal, not linear, planar, or bent.
- Electron Pair(s) on Arsenic:
- There is one lone pair of electrons on arsenic, which affects its shape and geometry.
Explanation:
Arsenic tribromide (AsBr₃) has a tetrahedral electron geometry due to the four electron pairs (three bonding and one lone pair). However, the lone pair on the arsenic atom reduces the molecular symmetry, making the molecular geometry trigonal pyramidal. This results in a three-dimensional, pyramidal shape, with the bromine atoms occupying three corners and the lone pair positioned above the arsenic atom, which repels the bonding pairs. This leads to the observed molecular geometry.
