chem: finish vsepr

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eggy 2020-11-10 14:25:52 -05:00
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@ -666,6 +666,7 @@ A **3D diagram** of a molecule is drawn similarly to three-dimensional Lewis str
- 90° angles are only present in molecules with five electron domains, and should be avoided in all other scenarios.
- The angle between the peripheral atoms should be labelled once for each distinct angle.
- for $\text{AX}_n\text{E}_m$ structures, where $n+m=4$, the angle between peripheral atoms is equal to $109.5° - 2.5m$.
- for $\text{AX}_n\text{E}_m$ structures, where $n+m=3$, the angle between peripheral atom is equal to $120°-3m$.
!!! example
The below 3D diagrams are for $\text{CH}_4$, $\text{NH}_3$, and $\text{H}_2\text{O}$, respectively. Note that the angle on $\text{NH}_3$ is supposed to be $107°$.
@ -679,16 +680,16 @@ Because of the addition of d orbitals beginning from $n=3$, elements in period 3
In molecules with 5 or 6 electron domains, their electron distribution is as follows, respectively:
<img src="/resources/images/56-domains.png" width=700>(Source: Kognity)</img>
In a trigonal bipyramid, the **equatorial** positions of domains refer to the position of the domains on the x- and z-dimensions (a trigonal plane). The domains along the y-dimension are have **axial** positions. The angle between the two is known as the **equatorial-axial** angle. Lone pairs are always placed in equatorial positions.
In a trigonal bipyramidal, the **equatorial** positions of domains refer to the position of the domains on the x- and z-dimensions (a trigonal plane). The domains along the y-dimension are have **axial** positions. The angle between the two is known as the **equatorial-axial** angle. Lone pairs are always placed in equatorial positions.
| AXE | Electron distribution | Molecular shape | Bond angle |
| --- | --- | --- | --- |
| $\text{AX}_5$ | trigonal bipyramidal | trigonal bipyramidal | equatorial=120°, equatorial-axial=90° |
| $\text{AX}_4\text{E}$ | trigonal bipyramidal | see-saw | |
| $\text{AX}_3\text{E}_2$ | trigonal bipyramidal | t-shaped | |
| $\text{AX}_4\text{E}$ | trigonal bipyramidal | see-saw | equatorial=117°, equatorial-axial=90° |
| $\text{AX}_3\text{E}_2$ | trigonal bipyramidal | t-shaped | equatorial-axial=90° |
| $\text{AX}_2\text{E}_3$ | trigonal bipyramidal | linear | 180° |
| $\text{AX}_6$ | octahedral | octahedral | 90° |
| $\text{AX}_5\text{E}_6$ | octahedral | square pyramidal | |
| $\text{AX}_5\text{E}_6$ | octahedral | square-based pyramidal | 88.5° |
| $\text{AX}_4\text{E}_2$ | octahedral | square planar | 90° |
!!! example