定义Definition
四面体形是中心原子与四个原子相连、四个原子位于四面体顶点的分子构型。当四个原子相同时为正四面体，键角为 109.5°（精确值 109°28′），如 CH₄、CCl₄、NH₄⁺。
Tetrahedral geometry is the molecular shape in which a central atom is bonded to four atoms at the corners of a tetrahedron. When all four are identical it is a regular tetrahedron with bond angles of 109.5° (exactly 109°28′), as in CH₄, CCl₄ and NH₄⁺.
成因Why the shape forms
中心原子周围有四个成键电子对、没有孤对电子时，四对电子相互排斥，在三维空间中距离最远的排列就是四面体，键角 109.5°，而不是平面正方形的 90°。用杂化轨道理论描述，中心原子为 sp³ 杂化。
With four bonding pairs and no lone pairs on the central atom, the arrangement that keeps the four pairs furthest apart in three dimensions is a tetrahedron, at 109.5°, not a square plane at 90°. In hybridisation terms the central atom is sp³.
例子Examples
分子：CH₄、CCl₄、SiH₄、SiCl₄。离子：NH₄⁺、BF₄⁻、SO₄²⁻、PO₄³⁻、MnO₄⁻、[CoCl₄]²⁻、[CuCl₄]²⁻（在许多盐中略有变形）。巨型结构：金刚石和二氧化硅中每个 C 或 Si 都处于四面体中心。
Molecules: CH₄, CCl₄, SiH₄, SiCl₄. Ions: NH₄⁺, BF₄⁻, SO₄²⁻, PO₄³⁻, MnO₄⁻, [CoCl₄]²⁻ and [CuCl₄]²⁻ (slightly distorted in many salts). Giant structures: each C in diamond and each Si in silicon dioxide sits at the centre of a tetrahedron.
与相关构型的比较Related shapes
四个电子对区域中有孤对电子时，电子对仍呈四面体排布，但分子构型改变：一对孤对为三角锥形（NH₃，107°），两对孤对为 V 形（H₂O，104.5°）。四个取代基不同的四面体碳原子没有对称面，是手性中心，存在对映异构体。
When some of the four regions are lone pairs, the electron pairs are still tetrahedral but the molecular shape changes: one lone pair gives trigonal pyramidal (NH₃, 107°), two give bent (H₂O, 104.5°). A tetrahedral carbon with four different groups has no mirror plane, is a chiral centre and has enantiomers.
年表Timeline
- 1874
范特霍夫与勒贝尔各自提出碳原子的四面体结构，解释旋光异构
van 't Hoff and Le Bel independently propose the tetrahedral carbon atom to explain optical isomerism
- 1913
布拉格父子用 X 射线衍射证实金刚石中的四面体碳
The Braggs confirm tetrahedral carbon in diamond by X-ray diffraction