Which of the following electron-pair geometries is not consistent with a linear molecular geomet

Which of the following electron-pair geometries is not...

Key Concepts

Linear Molecular Geometry

Linear molecular geometry is a specific shape wherein the atoms in a molecule are arranged in a straight line with a bond angle of 180°. For a molecule to have a linear shape, the central atom must have two regions of electron density that are directly opposite each other. This geometry can be achieved in molecules with different electron-pair geometries (such as tetrahedral or octahedral) if the bonding pairs are positioned 180° apart; however, in a trigonal planar arrangement, the inherent 120° separation prevents achieving a linear shape with only two bonding sites.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. It states that electron pairs will arrange themselves as far apart as possible to minimize repulsion, which determines the overall electron-pair geometry around the central atom.

Electron-Pair Geometry

Electron-pair geometry refers to the spatial arrangement of all electron pairs (both bonding pairs and lone pairs) around the central atom. Common geometries include linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. This concept is crucial for understanding how different groups attached to the central atom can be arranged relative to one another.

Bonding Pairs and Lone Pairs Arrangement

In molecular geometry, the positions of bonding pairs (electron pairs involved in bonds between atoms) are determined after accounting for the overall electron-pair geometry dictated by VSEPR theory. Lone pairs also contribute to the electron repulsion and influence the observed molecular shape. Understanding how bonding pairs are arranged, particularly when some positions are occupied by lone pairs, is key to predicting accurate molecular geometries.

Transcript

00:01 Here we are told that assuming we have three atoms per molecule, we want to know which of the following geometries are not linear.

00:07 Electron geometries.

00:08 So we're looking at electron groups around the central atom.

00:14 So we have three of them.

00:16 We've got tetrahedral, which has an electron geometry with four groups, octahedral, six electron groups, and trigonal planar, three electron groups.

00:25 So for our first one, we've got tetrahedral.

00:27 So normally we would have something in the center bonded to.

00:31 Four other things, meaning we definitely would not have a linear molecule with four our bonds around the tetrahedral molecule because we have four things.

00:45 The bond angles are about 109 degrees.

00:47 So if we look at one that has three bonds, we've got one bond here.

00:55 But since we've got two bonds and we need four electron groups, we're going to have to add two lone pairs.

01:01 So now we've got two lone pairs around the same.

01:05 Central atom and two bonds.

01:08 So we could liken a molecule like this to water.

01:13 So we would have h2o, we'd have an oxygen in the middle with two lone pairs, and then we'd have two hydrogens bonded to it, and we know that water's not a linear molecule because those lone pairs push these bonds down.

01:28 So instead of them being linear at 180 degrees, they are pushed down and the bond angle is smaller, so it's less than 180 degrees.

01:36 So we would say that a tetrahedral molecule with three atoms bonded together cannot be linear.

01:44 So this is not linear.

01:50 Now for our second one, we have an octahedral molecule.

01:53 Normally we would have six things bonded together.

01:59 So we have four things bonded equatorially to the central atom and two things in the axial position.

02:07 But in this case, we can only have three atoms.

02:12 Two things bonded to our central atom again, like in our first example, two things bonded to the central atom and we'll make the other four groups loan pairs...

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