AXE method
In chemistry, The AXE method is commonly used in formatting molecules to fit the VSEPR model that aims to explain molecular geometry.
The A represents the central atom and always has an implied subscript one. The X represents how many sigma bonds are formed between the central atoms and outside atoms. Multiple covalent bonds (double, triple, etc) count as one X. The E represents the number of lone electron pairs present outside of the central atom. The sum of X and E represents the total number of hybridised orbitals, which determines the type of hybridisation undergone in the central atom. Once the AXE formula has been found, the following table will predict the geometric configuration around the central atom:
| Type | Shape | Examples | Bond Angle |
|---|---|---|---|
| AX1E* | Linear (N/A) | HF, O2 | |
| AX2E0 | Linear | BeCl2, HgCl2, CO2 | |
| AX2E1 | Bent | SO2, O3 | |
| AX2E2 | Bent | H2O | |
| AX2E3 | Linear | XeF2, I3- | |
| AX3E0 | Trigonal planar | BF3, CO32-, NO3-, SO3 | 120° |
| AX3E1 | Trigonal Pyramidal | NH3 | |
| AX3E2 | T-shaped | ClF3, BrF3 | |
| AX4E0 | Tetrahedral | CH4 | |
| AX4E1 | Seesaw | SF4 | |
| AX4E2 | Square Planar | XeF4 | |
| AX5E0 | Trigonal Bipyramidal | PCl5 | |
| AX5E1 | Square Pyramidal | BrF5 | |
| AX6E0 | Octahedral | SF6 | |
| AX6E1 | Pentagonal pyramidal | XeF6 | |
| AX7E0 | Pentagonal bipyramidal | IF7 |