Predict the geometric shapes of (a) CO ; (b) SiCl4; (c) PH3 ; (d) ICl3 ; (e) SbCl5 ; (f) SO2 ; (

Predict the geometric shapes of (a) CO ; (b) SiCl4; (c) PH3...

Key Concepts

Lone Pair Effects

Lone pairs exert greater repulsive force than bonding pairs, which can distort ideal bond angles and influence the observed shape of the molecule. Their presence on a central atom can lead to geometries like bent or trigonal pyramidal which differ from the corresponding idealized geometries.

Molecular Geometry vs. Electron Geometry

While electron geometry considers all electron domains, molecular geometry focuses specifically on the positions of the atoms. The presence of lone pairs, which do not appear in the molecular shape, can alter the observed geometry from the ideal molecular and electron domain shapes predicted by VSEPR theory.

Symmetry and Molecular Shape

Molecular symmetry plays a crucial role in determining properties such as polarity and bond angles. High symmetry in molecules, such as those with tetrahedral, octahedral, or trigonal bipyramidal arrangements, typically results in non-polar molecules, whereas lower symmetry due to lone pairs can create dipole moments.

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the geometric arrangement of electron pairs around a central atom in a molecule or ion. It states that electron pairs, both bonding and lone pairs, will arrange themselves as far apart as possible to minimize repulsion, thereby determining the overall shape of the molecule.

Electron Domain Geometry

This concept involves counting regions of electron density (referred to as electron domains) around a central atom, including both lone pairs and bonds (single, double, or triple bonds). The spatial arrangement of these electron domains establishes the electron domain geometry, such as linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral.

Transcript

00:01 Here we will be using the vsepr theory to determine the geometric shape of our given molecules.

00:06 So, for example, on our first one, carbon monoxide, we first calculate the number of valence electrons.

00:12 We see that there are 10.

00:14 And then looking at our lewis structure that we draw, we will look at the central atom and determine how many electron groups are surrounding it.

00:23 And so i chose carbon.

00:25 Oxygen also works.

00:27 It will have the same number.

00:28 And so there will be two surrounding electron groups here.

00:34 And so going over to your vsepr table, you'll see that this means that it is linear.

00:42 So let's go ahead and move on to our next one, sicl4.

00:48 And so calculating the total number of valence electrons and then drawing out the lewis structure, you can see here that there will be a total of four electron groups surrounding the central atom.

01:00 And there are no lone pairs, and so this means that it will be tetrahedral shape.

01:10 Okay, moving on to our next one, we have ph3, seeing that there are eight valence electrons, and then drawing out the lewis structure, we will have a total of four surrounding electron groups.

01:26 But this time, you have to notice that one of these is a lone pair.

01:31 And so going to your table, when one of them is a lone pair out of the four electron groups, this means that it will be trigonal pyramidal pyramidal.

01:50 Okay, let's go to our next one.

01:52 And this is one that will have to have an expanded octet.

01:57 And luckily, iodine fits this rule because it's in the period three or below.

02:03 And so it can have more than eight electrons...

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