Draw electron-dot structures for the following molecules,...

Draw electron-dot structures for the following molecules, indicating any unshared electron pairs. Which of the compounds are likely to act as Lewis acids and which as Lewis bases? (a) $\mathrm{AlBr}_{3}$ (b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2} \quad$ (c) $\mathrm{BH}_{3}$ (d) HF (e) $\mathrm{CH}_{3} \mathrm{SCH}_{3}$ (f) TiCl $_{4}$

Draw electron-dot structures for the following molecules, indicating any unshared electron pairs. Which of the compounds are likely to act as Lewis acids and which as Lewis bases?
(a) $\mathrm{AlBr}_{3}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2} \quad$ (c) $\mathrm{BH}_{3}$
(d) HF
(e) $\mathrm{CH}_{3} \mathrm{SCH}_{3}$
(f) TiCl $_{4}$

Key Concepts

Octet Rule

The octet rule is a principle that atoms tend to combine in such a way that each atom has eight electrons in its valence shell, attaining a configuration similar to noble gases. This rule guides the construction of electron-dot structures and helps predict the stability and potential reactivity of a molecule, which in turn relates to its ability to act as a Lewis acid or base.

Electron-Dot Structures

Electron-dot structures, or Lewis structures, are visual representations that show how valence electrons are distributed around atoms in a molecule. They help in understanding the bonding and arrangement of electrons, illustrating both shared electrons (in bonds) and unshared electrons (lone pairs). This concept is crucial for predicting molecular geometry and reactivity.

Lewis Acids and Bases

The Lewis acid-base theory characterizes acids as electron pair acceptors and bases as electron pair donors. By examining electron-dot structures for the presence of electron deficiency or accessible lone pairs, one can determine which species are likely to act as acids (electron acceptors) or bases (electron donors), which is key to understanding their reactivity in chemical interactions.

Unshared Electron Pairs

Unshared electron pairs refer to electrons that are not involved in bonding. Their presence in a molecule often increases the likelihood of the molecule acting as a Lewis base because these lone pairs are available for donation to electron-deficient species. Recognizing unshared pairs in electron-dot structures is fundamental for evaluating the basicity of compounds.

Transcript

00:01 We want to draw the electron dot structures for each of the following molecules, indicating any unshared electron pairs, and they also want us to determine how likely each of these will be and acting as a lewis acid or a lewis base.

00:19 All right, so let's go ahead and start with aluminum tribromide.

00:25 And so if you were to go through the whole process, you should first start.

00:36 With the aluminum in the center, bromines on the outside.

00:39 And then the bromines are going to have three pairs of lump pairs each.

00:46 And if you were to count up how many electrons we have here, you would see you would match with what we normally have.

00:54 And now the bromines really want to keep the electrons for themselves.

00:58 So these probably aren't going to do anything.

01:01 So we need to focus on this aluminum here.

01:05 Well, it has no electrons to donate.

01:07 So we'll probably want to accept electrons.

01:10 And so remember, lewis bases donate electrons, and lewis acids accept electrons.

01:26 So in this case, this is wanting to accept electrons, and it makes sense because aluminum has a lot of metal properties.

01:35 So this would be a lewis, since it wants to accept electrons.

01:45 Now let's draw out this amine over here in part b.

01:50 So we have a carbon, a carbon, a nitrogen.

01:53 So this carbon here would have three hydrogens.

01:59 The next one has two.

02:01 And this nitrogen here has two.

02:03 And then it's also going to have a lone pair.

02:08 Now, the carbons don't seem like they're going to really want to do anything, nor are the hydrogens.

02:15 But notice over here, this nitrogen has this lone pair that it may want to donate.

02:22 And we know amides or nitrogen is normally pretty basic.

02:29 So it could be very easy for an acid to donate to this.

02:34 Or we could just use this to attack something else.

02:37 So it's more likely that this is going to be a lewis base...

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