Predict the molecular structure for each of the following. (See Exercises 115 and 116.) a. BrFI2

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

Key Concepts

VSEPR Theory

VSEPR (Valence Shell Electron Pair Repulsion) theory is a fundamental concept for predicting the three-dimensional arrangement of atoms in a molecule. It explains that electron domains (which include bonding pairs and lone pairs) around a central atom will position themselves as far apart as possible, minimizing repulsion and thereby determining the molecule’s geometry. This theory is used to predict the molecular structures in problems involving different substituents and electron pairs.

Expanded Octet Concept

The expanded octet concept addresses the ability of elements in the third period and beyond to accommodate more than eight electrons in their valence shell. This is relevant in molecular structure prediction when central atoms, such as bromine, xenon, or tellurium, are bonded to multiple atoms, allowing them to form additional bonds beyond the typical octet. This concept is crucial when predicting the structures of molecules with multiple atoms attached to a central atom.

Axial/Equatorial Positioning

In molecules with geometries such as trigonal bipyramidal or square pyramidal, the positioning of substituents is often described in terms of axial and equatorial positions. Axial positions are aligned along the principal axis and are typically associated with greater repulsive interactions, whereas equatorial positions lie in a plane and offer more space. This concept is important in determining the most stable arrangements when different substituents, especially those varying in size or electronegativity, are involved.

Isomerism in Molecular Structures

Isomerism in molecular structures refers to the phenomenon where molecules with the same molecular formula can have different spatial arrangements of atoms. For molecules with non-equivalent substituents around a central atom, there can be multiple valid structural arrangements (isomers), each with distinct physical and chemical properties. Recognizing this possibility is essential when drawing all possible structures for a given formula.

Electronegativity Effects on Substituent Arrangement

Electronegativity effects play a key role in the positioning of substituents around a central atom. More electronegative atoms or groups often occupy positions that minimize electronic repulsions and maximize stability, sometimes preferring equatorial rather than axial positions in certain geometries. This consideration helps in predicting the detailed arrangement of atoms in molecules where multiple arrangements are possible.

Transcript

00:01 Problem 167 says to predict and draw the possible molecular structures for the following molecules.

00:08 The problem also says that there are several different configurations that can be drawn with the same central atom and to account for those structures.

00:18 So for the top one here, we have a central bromine bound by a fluorine and two iodine groups.

00:29 So keep in mind, of course, that the first thing we should always think about when drawing a lewis structure, is the number of valence electrons we need to account for.

00:40 So since all four of these atoms are halogens, all of them have seven valence electrons, giving us a total of 28 that we need to think about.

00:54 So the first possible configuration here is the two fluorians at the top, sorry, the fluorine at the top of the bromine here and the two iodines at the bottom.

01:14 Now because again these are halogens, we can give each the fluorine and the iodines three lone pairs of electrons.

01:26 And by accounting for these eight electrons for each, the fluorine and the two iodines, so far that's 24 total electrons.

01:39 So we need to add four more, and that can be done by giving the bromine two lone pairs.

01:50 Now, as you can see, the iodines here are 90 degrees apart, but you can imagine a scenario where instead of being separated by 90 degrees, the iodines are separated by 180 degrees.

02:08 And so as you can see here, the other possible structure for this particular molecule is simply flipping this drawing upside down.

02:25 And then the other possibility is separating the two iodines with the fluorine here.

02:33 So for part b, we can go about doing the same thing.

02:37 I'll draw this over here to give us some space for part c.

02:42 We have a xenon in the center here, and we can bind to that the two oxygens and the two fluorines.

02:58 So just like before, we should count up the electrons that we need to think about...

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