The AlI3 molecule has an incomplete octet around Al. Draw...

The $\mathrm{AlI}_{3}$ molecule has an incomplete octet around Al. Draw three resonance structures of the molecule in which the octet rule is satisfied for both the $\mathrm{Al}$ and the I atoms. Show formal charges.

Key Concepts

Formal Charges

Formal charges provide a method for keeping track of electron distribution in a molecule by comparing the number of valence electrons in the isolated atom with the number assigned in the Lewis structure. They are critical for evaluating the stability of different resonance forms, as structures with formal charges that are minimized and correctly placed are generally considered more stable.

Incomplete Octet

An incomplete octet refers to situations where an atom does not have eight electrons in its valence shell; this can be characteristic of electron-deficient atoms. Understanding incomplete octets is important because certain atoms are capable of expanding their valence shells through resonance or accepting additional electron pairs, leading to stable molecular structures even when the octet is not initially satisfied.

Resonance Structures

Resonance structures are different valid Lewis structures that represent the same molecule. They illustrate the idea that electrons can be delocalized across multiple atoms rather than being confined to a single location. This concept is crucial in understanding molecular stability and reactivity, as the actual electronic structure of the molecule is a hybrid of these contributing forms.

Octet Rule

The octet rule is a fundamental principle in chemistry which states that atoms tend to combine in such a way that each atom has eight electrons in its valence shell, achieving a noble gas configuration. Although there are exceptions, this rule is a primary guideline in drawing Lewis structures and predicting molecular structures in many compounds.

Transcript

00:01 Hello, so today we'll be looking at possible resonance forms for aluminum iodide, this molecule with this compound right here.

00:12 So let's first count up the valence electrons.

00:16 So aluminum has three valence electrons, iodine has seven, and there are three of them.

00:24 Let's add them up, three times seven is 21, plus three is 24 electrons.

00:32 So let's count up how many need.

00:35 So aluminum needs eight, id needs eight, and there are three of them.

00:41 So that's a total of 32 electrons.

00:46 So if we take how many we need, subtract how many we have and divide by two, that will usually give you how many bonds you need.

00:56 So in this case, four bonds.

00:59 So if you just draw three bonds around aluminum and you just add lone pairs to iodide, you will notice that iodide has complete octats, and if you count out the electrons, 24, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, we have the correct amount of electrons.

01:35 But three bonds isn't enough because aluminum doesn't have a full octet.

01:42 If you look at the formal charges, the formal charges are all zero, but aluminum doesn't have a full octet.

01:51 So what we would do is we would add a bond.

01:57 And now look, we have, now aluminum has a full octet.

02:07 Iodide has full all of the iodines have a full octet as well.

02:12 So this works...

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