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 (sometimes known as the steric number), which determines the type of hybridisation undergone in the central atom (2 = sp, 3 = sp², 4 = sp³, 5 = sp³d, 6 = sp³d², 7 = ?). Once the AXE formula has been found, the following table will predict the geometric configuration around the central atom:

**Caution:** the notation in this diagram differs from the article. Here E represents the central atom (called A in the article); X represents outside atoms (same as the article); and **two dots** represents a lone pair (called E in the article). The last two entries on the last rwo (AX₃E₃, AX₂E₄) are not found in the article, and steric number 7 is not listed in the table. Entries with only one outside atom are also not listed in the table.

Type	Shape	Examples
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, CO₃^2-, NO₃^-, SO₃
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