The Group 5 A elements can form molecules or ions that...

The Group 5 A elements can form molecules or ions that involve three, five, or six covalent bonds; $\mathrm{NH}_{3}, \mathrm{AsCl}_{5}$, and $\mathrm{PF}_{6}^{-}$ are examples. Draw the Lewis structure for each of these substances, and predict the molecular structure and hybridization for each. Why doesn't $\mathrm{NF}_{5}$ or $\mathrm{NCl}_{6}^{-}$ form?

Key Concepts

Octet Rule and Expanded Octet

The octet rule states that atoms tend to form bonds until they are surrounded by eight electrons in their valence shell. However, certain heavier atoms, with available d orbitals, can exceed this octet, forming species with an 'expanded octet.' Lighter elements like nitrogen do not have accessible d orbitals, which restricts them to following the octet rule, explaining why some hypervalent species (e.g., NF5) do not form.

Electronegativity and Steric Considerations

Electronegativity and steric factors play a crucial role in determining whether a molecule can stably accommodate additional bonds. Highly electronegative or small central atoms may not effectively disperse the increased electron density or spatial demands of multiple substituents, thereby limiting the formation of species with high coordination numbers.

Hybridization

Hybridization describes the mixing of atomic orbitals to create new hybrid orbitals that explain the observed bonding geometries in molecules. The type of hybridization (such as sp3, sp3d, or sp3d2) correlates with the electron-domain geometry predicted by VSEPR theory, providing insight into bond angles and molecular structure.

VSEPR Theory

The Valence Shell Electron Pair Repulsion theory is used to predict the shape of a molecule by considering that electron pairs (bonding and nonbonding) around a central atom repel each other and adopt arrangements that minimize these repulsions. This theory allows us to deduce the three?dimensional molecular geometry from the number and types of electron pairs.

Lewis Structures

Lewis structures are diagrams that depict the arrangement of valence electrons among atoms in a molecule. They show how atoms share electrons through bonds and account for lone electron pairs, which helps in understanding connectivity and reactivity in molecules.

Transcript

00:01 So let's take a look at how to do this problem.

00:03 So for the first one, we're going to have this is the structure.

00:07 So we're just going to have the tribunal grammatical structure.

00:15 There's one lone pair on the nitrogen and three months to the hydrogen.

00:19 Then we're going to just predict the hybridization.

00:27 So the hybridization will be s.

00:30 P.

00:30 Three because the lone pair contributes the same amount of organization.

00:34 At the box.

00:34 We go s.

00:35 P one p two, p three and therefore will be sp three, that's ammonia and then we'll move on to the next one.

00:43 So this is tribunal five by pure amital.

00:49 Because basically what this is, it's two of these combined, it has that shape to it.

00:55 This is what it's going to look like.

00:56 So we'll have is in the center who have some quarries and we're going to have three of them bonded to the center like that.

01:18 And you can see we call this tribunal bip aram inal because we have a triangle or a pyramid with a triangular bottom and then we have another one on the bottom.

01:34 That's why this tribunal by pure.

01:37 And then the bonding hybridization will be 123.

01:41 So it s...

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