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AX 2 E 1 molecules, such as SnCl 2, have only one lone pair and the central angle about 120° (the centre and two vertices of an equilateral triangle). They have three sp 2 orbitals. There exist also sd-hybridised AX 2 compounds of transition metals without lone pairs: they have the central angle about 90° and are also classified as bent.
The difference between lone pairs and bonding pairs may also be used to rationalize deviations from idealized geometries. For example, the H 2 O molecule has four electron pairs in its valence shell: two lone pairs and two bond pairs. The four electron pairs are spread so as to point roughly towards the apices of a tetrahedron.
Angular: Angular molecules (also called bent or V-shaped) have a non-linear shape. For example, water (H 2 O), which has an angle of about 105°. A water molecule has two pairs of bonded electrons and two unshared lone pairs. Tetrahedral: Tetra-signifies four, and -hedral relates to a face of a solid, so "tetrahedral" literally means "having ...
However, further down in the group (silicon, germanium, and tin), formal triple bonds have an effective bond order 2 with one lone pair (figure B [19]) and trans-bent geometries. In lead, the effective bond order is reduced even further to a single bond, with two lone pairs for each lead atom (figure C [19]).
In the gas phase, a single water molecule has an oxygen atom surrounded by two hydrogens and two lone pairs, and the H 2 O geometry is simply described as bent without considering the nonbonding lone pairs. [citation needed] However, in liquid water or in ice, the lone pairs form hydrogen bonds with neighboring water molecules. The most common ...
Bent's rule can be extended to rationalize the hybridization of nonbonding orbitals as well. On the one hand, a lone pair (an occupied nonbonding orbital) can be thought of as the limiting case of an electropositive substituent, with electron density completely polarized towards the central atom.
For the hydrogen fluoride molecule, for example, two F lone pairs are essentially unhybridized p orbitals of π symmetry, while the other is an sp x hydrid orbital of σ symmetry. An analogous consideration applies to water (one O lone pair is in a pure p orbital, another is in an sp x hybrid orbital).
The T-shaped geometry is related to the trigonal bipyramidal molecular geometry for AX 5 molecules with three equatorial and two axial ligands. In an AX 3 E 2 molecule, the two lone pairs occupy two equatorial positions, and the three ligand atoms occupy the two axial positions as well as one equatorial position. The three atoms bond at 90 ...