A molecule with the formula AB2, in which A and B represent...

A molecule with the formula $\mathrm{AB}_{2}$, in which $\mathrm{A}$ and $\mathrm{B}$ represent different atoms, could have one of three different shapes. Sketch and name the three different shapes that this molecule might have. Give an example of a molecule or ion for each shape.

Key Concepts

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the three?dimensional arrangement of atoms in a molecule based on the repulsions between electron pairs around a central atom. It emphasizes that electron pairs, both bonding and nonbonding, will adopt positions that minimize repulsive interactions, thereby determining the molecular geometry.

Electron Domain Geometry

Electron domain geometry refers to the spatial arrangement of all electron pairs (both bonding and lone pairs) around a central atom. Depending on whether there are 2, 3, or 4 electron domains, the electron geometry can be linear, trigonal planar, or tetrahedral, respectively. In an AB2 type molecule, different numbers of lone pairs on the central atom lead to different domain geometries which in turn influence the observed molecular shape.

Influence of Lone Pairs

Lone pairs of electrons occupy more space than bonding pairs because they are localized on the central atom, leading to greater repulsive interactions. This difference in repulsion can significantly alter bond angles and thus the molecular shape. For an AB2 molecule, the absence of lone pairs yields a linear shape (bond angles of 180°), whereas the presence of one or two lone pairs results in bent shapes with bond angles that are somewhat reduced from the idealized angles (around 120° for one lone pair with trigonal planar geometry, and around 104.5° for two lone pairs with tetrahedral geometry).

Transcript

0:00 Good day.

00:02 In this question, we are given a molecule of the form ab2, and we are told that it can have three possible different shapes.

00:11 So in this question, we need to sketch the three different shapes, name them, and also give examples that this molecule might be a molecule or ion.

00:22 Okay, so i've also put you at the table for the vs -epr geometries.

00:28 So let's start off by lighting down the different possible shapes.

00:35 So we are dealing with a, b2, where a and b are atoms.

00:43 Okay, so the first arrangement that we can have would be a is in the center, a and then b, and then b, and then the bonding electrons.

01:00 Okay, so this is where we just got the two.

01:02 Two regions of electron density, no lone atoms, no lone per electron, sorry.

01:11 So in this case, this would give us two electron pairs.

01:15 This would give us a linear structure.

01:19 So this is a linear molecular structure.

01:29 Linear molecular structure.

01:33 And an example would be co2, as well as it has got two electron pairs and zero loan pairs.

01:46 And then a second possible structure.