Octahedral Molecules vs. Trigonal Planar Molecules

Attribute	Octahedral Molecules	Trigonal Planar Molecules
Number of atoms	8	3
Geometry	Octahedral	Trigonal planar
Bond angles	90 degrees	120 degrees
Number of lone pairs	0	0
Examples	SF6, [Co(NH3)6]3+	BH3, BF3

Structure

Octahedral molecules have a central atom surrounded by six other atoms or groups of atoms, arranged in a symmetrical octahedral shape. This results in a total of eight electron pairs around the central atom, with six bonding pairs and two lone pairs. On the other hand, trigonal planar molecules have a central atom surrounded by three other atoms or groups of atoms, arranged in a flat, triangular shape. This results in a total of four electron pairs around the central atom, with three bonding pairs and one lone pair.

Bond Angles

In octahedral molecules, the bond angles between the central atom and the surrounding atoms are all equal at 90 degrees. This is due to the symmetrical arrangement of the atoms around the central atom. In contrast, trigonal planar molecules have bond angles of 120 degrees between the central atom and the surrounding atoms. This is because the three atoms are arranged in a flat, triangular shape, resulting in equal bond angles.

Geometry

The geometry of octahedral molecules is described as having six electron pairs arranged in an octahedral shape around the central atom. This results in a geometry that is symmetrical and three-dimensional. On the other hand, trigonal planar molecules have a geometry that is described as having three electron pairs arranged in a flat, triangular shape around the central atom. This results in a geometry that is planar and two-dimensional.

Examples

• Examples of octahedral molecules include SF6 (sulfur hexafluoride) and Ni(CO)4 (nickel tetracarbonyl).
• Examples of trigonal planar molecules include BF3 (boron trifluoride) and SO3 (sulfur trioxide).

Hybridization

Octahedral molecules typically exhibit sp3d2 hybridization, where the central atom's s and p orbitals combine with five d orbitals to form six equivalent sp3d2 hybrid orbitals. This allows for the formation of six sigma bonds with the surrounding atoms. Trigonal planar molecules, on the other hand, exhibit sp2 hybridization, where the central atom's s and p orbitals combine to form three equivalent sp2 hybrid orbitals. This allows for the formation of three sigma bonds with the surrounding atoms.

Stability

Octahedral molecules are generally more stable than trigonal planar molecules due to the symmetrical arrangement of atoms around the central atom. This symmetrical arrangement minimizes repulsion between electron pairs, resulting in a more stable molecule. Trigonal planar molecules, on the other hand, may experience more repulsion between electron pairs due to the flat, triangular arrangement of atoms, leading to slightly lower stability compared to octahedral molecules.

Reactivity

Octahedral molecules tend to be less reactive than trigonal planar molecules due to the higher stability of the octahedral geometry. The symmetrical arrangement of atoms in octahedral molecules results in less strain on the central atom, making it less likely to undergo chemical reactions. Trigonal planar molecules, on the other hand, may exhibit higher reactivity due to the slightly lower stability of the trigonal planar geometry, making them more prone to chemical reactions.