The capital A is the central atom, but I couldn't find any lower case 'a' in the VSEPR.
The Valence shell electron pair repulsion, or VSEPR is a simple technique for predicting the shape or geometry of atomic centers. The VSEPR formula is used in small molecules and molecular ions.
The formula ab3 corresponds to a trigonal planar shape in VSEPR theory. This means that the central atom is surrounded by three bonded atoms and has a bond angle of 120 degrees between them.
The VSEPR formula for water (H2O) is AX2E2, where A represents the central atom and X represents the bonding pairs of electrons, while E represents the lone pairs of electrons.
Electron pairs
VSEPR only shows the geometric shape of the element
Ax3e
The Valence shell electron pair repulsion, or VSEPR is a simple technique for predicting the shape or geometry of atomic centers. The VSEPR formula is used in small molecules and molecular ions.
Ax5
The formula ab3 corresponds to a trigonal planar shape in VSEPR theory. This means that the central atom is surrounded by three bonded atoms and has a bond angle of 120 degrees between them.
The VSEPR formula for a nitrogen atom as the central atom in glycine is AX3E, which corresponds to trigonal pyramidal geometry. Nitrogen has three bonded atoms (A) and one lone pair of electrons (E), resulting in a total of four electron groups around the central nitrogen atom.
Ozone is a molecule with formula O3. It is bent in shape and has sp and sp2 hybridised oxygen atoms.
The VSEPR formula for water (H2O) is AX2E2, where A represents the central atom and X represents the bonding pairs of electrons, while E represents the lone pairs of electrons.
D. FCl3 has a VSEPR formula of AXËÄ. This notation indicates the molecular geometry and electron pair arrangement around the central atom. In this case, FCl3 has a trigonal bipyramidal shape with 3 bonding pairs and 2 lone pairs around the central atom.
The VSEPR model is used mainly to determine molecular shape.
VSEPR is a conceptual model, as it has not been directly observed.
The molecular geometry of CHCl3, according to VSEPR theory, is tetrahedral.
The molecular geometry of SO2 according to the VSEPR theory is bent.