Axial position

Definition

Axial position refers to the positions along the axis of a trigonal bipyramidal molecular geometry, typically occupied by atoms or groups. These positions are aligned perpendicular to the plane containing the equatorial positions.

5 Must Know Facts For Your Next Test

1. In a trigonal bipyramidal molecular geometry, there are two axial positions and three equatorial positions.
2. Atoms in axial positions experience more repulsion compared to those in equatorial positions due to 90° bond angles with three other atoms.
3. Axial bonds are generally longer than equatorial bonds due to increased repulsion forces.
4. Substituents prefer equatorial positions over axial when possible because of lower steric hindrance and electron repulsion.
5. An example of a molecule with distinct axial and equatorial positions is phosphorus pentachloride (PCl$_5$).

Review Questions

• How many axial and equatorial positions are present in a trigonal bipyramidal structure?
• Why do atoms in axial positions experience more repulsion compared to those in equatorial positions?
• Provide an example of a molecule that exhibits both axial and equatorial positions.

Related terms

Equatorial Position: Positions in a trigonal bipyramidal structure that lie in the same plane, usually associated with lower steric hindrance.

Trigonal Bipyramidal: $AX_5$ molecular geometry with three atoms forming an equilateral triangle (equatorial) and two atoms positioned axially.

$PCl_5$: $Phosphorus pentachloride$, a compound that adopts a trigonal bipyramidal structure at room temperature.