Predict the molecular structure for each of the following. (See Exercises 105 and 106 . ) a. BrF

Predict the molecular structure for each of the following....

Key Concepts

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a foundational model for predicting the shapes of molecules. It is based on the idea that electron pairs around a central atom will arrange themselves as far apart as possible in order to minimize repulsion. This model helps in determining the molecular geometry by considering both bonding pairs and lone pairs of electrons, which is crucial when multiple structures are possible for a given formula.

Central Atom Determination

Identifying the central atom in a molecule is key to correctly applying VSEPR theory. The central atom is typically the one with the lowest electronegativity (excluding hydrogen) and the greatest capacity to form multiple bonds. It is the atom to which most other atoms or groups are attached, and its available orbitals may even expand beyond the octet rule, which is significant for elements in the third period or beyond.

Electron Domain Geometry

Electron domain geometry involves counting all regions of electron density (both bonding pairs and lone pairs) around the central atom. This counting determines the electron pair geometry, which sets a framework for the overall shape of the molecule. Understanding this concept is essential for predicting how ligands will be arranged in space, especially when they can occupy different positions such as axial or equatorial in geometries like trigonal bipyramidal or octahedral.

Expanded Octet

Some central atoms, particularly those in the third period and beyond, have the capacity to hold more than eight electrons in their valence shells. This phenomenon, known as an expanded octet, allows these atoms to accommodate additional substituents, leading to more complex molecular geometries. Recognizing when an expanded octet may occur is important for accurate structure prediction in molecules where the central atom forms five or six (or even more) bonds.

Geometric Isomerism and Multiple Arrangements

Many molecules, especially those with more than four electron domains, can adopt more than one valid structure by arranging ligands in different ways. These different arrangements, such as having a polar substituent in an axial versus an equatorial position in a trigonal bipyramidal structure, are examples of geometric isomerism. This concept is critical when a given molecular formula can lead to multiple structural isomers, each with potentially different chemical properties.

Transcript

00:02 Okay, today we're going to be predicting molecular structure, drawing of those structures of a few different compounds.

00:09 So the first one we have is brfi 2.

00:16 So first what i like to do is calculate all the valance electrons.

00:20 So here they're all halogens, so 2, 3, 4 times 7, or we have 28 electrons to work with.

00:30 Now we want to put the least electronegative atom in the next.

00:35 Middle.

00:42 So if we're using our electron negativity's chart, iodine would be our least electronegative.

00:56 And that means we can put iodine and bromine and 40 around it.

01:10 Then we want to fill in our valence electrons and count up how many we've used.

01:28 So so far, just as lone pairs, we've used 6, 12, 18.

01:33 And then the bonds, we've used 6 .6.

01:35 So that's.

01:35 That's 24 total, which means we have four more electrons to add in.

01:39 So whenever you have electrons left over, you add them on the central atom.

01:46 So right now, the way i've drawn this, we have a t -shaped geometry because this is a mimic of trigonal bi -paraminal.

02:04 So this is t -shaped.

02:15 Another way this could be drawn would be like this.

02:29 And this is, again, derived from trigonal bipramidal, but it actually ends up looking like trigonal planer without considering the electron pairs.

02:46 And then if we add one lone pair in axial position and one in the ectroporial position, this ends up looking like trigonal pyramidal.

03:10 Now, if you're looking at problem 11, this is the one example that we do see there on those variations, but those would be.

03:19 These other two would be possible probably not as likely though okay the next structure we have is xc .o2 f2 so we have 8 plus 12 plus 14 electrons to work with so in total that's 34 so xenon here is the least electrone negative because it's a noble gas so it's going to go in the middle and then we're going to put oxygen and flooring around it.

04:06 From my experience, oxygen typically requires two bonds.

04:11 So i'm just going to go ahead and add in double bonds here because i know the formal charge of oxygen will be satisfied if i do that.

04:18 And then i'm going to go ahead and add in my lone pairs...

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