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In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron.The bond angles are arccos(− 1 / 3 ) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane (CH 4) [1] [2] as well as its heavier analogues.
For example, methane (CH 4) is a tetrahedral molecule. Octahedral: Octa-signifies eight, and -hedral relates to a face of a solid, so "octahedral" means "having eight faces". The bond angle is 90 degrees. For example, sulfur hexafluoride (SF 6) is an octahedral molecule.
Most commonly, four bonds to a central atom result in tetrahedral or, less commonly, square planar geometry. The seesaw geometry occurs when a molecule has a steric number of 5, with the central atom being bonded to 4 other atoms and 1 lone pair (AX 4 E 1 in AXE notation).
The methane molecule (CH 4) is tetrahedral because there are four pairs of electrons. The four hydrogen atoms are positioned at the vertices of a tetrahedron, and the bond angle is cos −1 (− 1 ⁄ 3) ≈ 109° 28′. [16] [17] This is referred to as an AX 4 type of molecule. As mentioned above, A represents the central atom and X represents ...
where: α and β are the two greatest valence angles of coordination center; θ = cos −1 (− 1 ⁄ 3) ≈ 109.5° is a tetrahedral angle. When τ 4 is close to 0 the geometry is similar to square planar, while if τ 4 is close to 1 then the geometry is similar to tetrahedral.
Tetrahedrane is a hypothetical platonic hydrocarbon with chemical formula C 4 H 4 and a tetrahedral structure. The molecule would be subject to considerable angle strain and has not been synthesized as of 2023. However, a number of derivatives have been prepared.
Notably, white phosphorus, the most stable allotrope of phosphorus, is tetrahedral with the molecular formula P 4. [7] Arsenic can also exist as a metastable tetrahedral allotrope, As 4, known as yellow arsenic. Furthermore, mixed tetrahedral pnictogen molecules have been synthesized, such as AsP 3 [8] and, more recently, (PbBi 3)-. [9]
All sp 3-hybridized atoms are surrounded by atoms (or lone electron pairs) at the four corners of a tetrahedron. For instance in a methane molecule (CH 4) or an ammonium ion (NH + 4), four hydrogen atoms surround a central carbon or nitrogen atom with tetrahedral symmetry.