Difference Between Tetrahedral and Trigonal Pyramid (With Table)

A tetrahedron comes under the type of pyramid which has four “equal” triangular sides or faces if we’re talking about geometry. It is sometimes referred to as a triangular pyramid since its base can be any of those faces. It can also refer to a molecule containing a four-electrons-per-atom atom. These two electrons are bonded together, resulting in a perfect equal structure. 

Tetrahedral vs Trigonal Pyramid 

The main difference between a tetrahedral and trigonal pyramid is a tetrahedral structure is a type of pyramid which has four equal sides which are triangular in shape or faces that has 4 identical atoms. A trigonal pyramid has one atom at each corner and the other three same atoms.  

Although most tetrahedral elements have lesser symmetry, the points group Td includes carbon and other perfectly symmetric tetrahedral compounds. It’s feasible to make chiral tetrahedral substances. The core element of a tetrahedral object is surrounded by four additional atoms. Each of the surrounding atoms has a bond angle of 109.5 degrees because of the central element. 

The tetrahedral electron pair geometry that results in the trigonal pyramid molecular geometry of NH3 is a common example used of tetrahedral electron pair geometry that results in trigonal pyramid molecular geometry. Due to its five valence electrons, nitrogen requires three more electrons which are obtained by the other three hydrogen atoms to fulfil its octet. It results in a lone electron pair with no other atom with which to form a bond. 

Comparison Table Between Tetrahedral and Trigonal Pyramid 

Parameters of Comparison Tetrahedral PyramidTrigonal Pyramid 
Structure The tetrahedral structure is a type of pyramid which has four equal sides which are triangular in shape. A trigonal pyramid has one atom at each corner and the other three same atoms. 
Polarity Tetrahedral structures are non-polar compounds. Trigonal Pyramid belongs to polar compounds.  
Length  The tetrahedral structure always is equal in length to each other.  A trigonal pyramid’s structure will be influenced by the lone atom at its apex. 
Electric attraction  There is no electric attraction in tetrahedral compounds. There is an electric attraction in trigonal pyramid compounds.  
Constitution of atoms All four substituent atoms are the same.  A lone atom can have an effect on the shape of a trigonal pyramid. 

What is Tetrahedral Pyramid? 

A central atom is positioned in the heart of a tetrahedral molecular geometry, with four substituents located just at corners of the tetrahedron. When all four substituents are the same, as in methane (CH4) [1][2] and its heavier counterparts, the bond angles are cos1(13) = 109.4712206…° 109.5°.  

Points group Td includes carbon and other totally symmetric tetrahedral compounds, although most tetrahedral atoms have lower symmetry. Chiral tetrahedral compounds are possible. A tetrahedral item is one in which the core element is surrounded by four other atoms.  

The centre element forms bond angles of 109.5 degrees for each of the surrounding atoms. Methane, CH4, ammonia, NH3, and water, H2O, all contain four electron groups surrounding their core atom, giving them a tetrahedral form with bond angles of approximately 109.5°. 

 Natural gas contains the simplest hydrocarbon molecule, methane. The tetrahedral geometries at each carbon in a hydrocarbon chain are based on this molecule. The Lewis diagram for NH4+ displays N at the centre, with no lone electron pairs. 

 In comparison, ammonia, NH3, does contain a single pair. The fourth hydrogen atom attaches to the ammonia molecule as a hydrogen ion (with no electrons) to the nitrogen’s lone pair. 

What is Trigonal Pyramid? 

The trigonal pyramid molecular geometry of NH3 is an example of tetrahedral electron pair geometry resulting in trigonal pyramid molecular geometry. Because nitrogen has five valence electrons, it requires three extra electrons from three hydrogen atoms to complete its octet.  

This leaves a lone electron pair with no other atom to bind with. At approximately 109o bond angle, the three hydrogen atoms and the lone electron pair are as far apart as feasible. This is the geometry of tetrahedral electron pairs. 

The three connecting hydrogen atoms experience a little more repulsion from the lone electron pairs, resulting in a small compression to a 107o bond angle. Because the lone electron pair, while still exerting its impact, is undetectable when looking at molecular geometry, the molecule has trigonal pyramid molecular geometry.  

The electron pair geometry is tetrahedral, while the molecular geometry is a trigonal pyramid. The hydrogen ion linked with acid characteristics of certain compounds in aqueous solution is shown using the hydronium ion, which is a more precise way. 

An octet of electrons exists in Sulphur atoms and all oxygen atoms. In wines, sulfite and bisulfite ions are utilized as preservatives. It’s also a component of acid rain, which is created when Sulphur dioxide and water molecules mix. 

Main Differences Between Tetrahedral and Trigonal Pyramid 

  1. Tetrahedral structure is a type of pyramid with four “equal” triangular sides or faces whereas A trigonal pyramid, on the other hand, has one single atom at every corner and three identical atoms. 
  2. Tetrahedral are non-polar compounds whereas Trigonal Pyramid are polar compounds. 
  3. The tetrahedral structure always be equal in length to each other whereas A trigonal pyramid’s structure will be influenced by the lone atom at its apex. 
  4. There is no electric attraction in tetrahedral compounds whereas There is electric attraction in trigonal pyramid compounds. 
  5. All four substituent atoms are same whereas Lone atom can have effect on the shape of trigonal pyramid. 

Conclusion 

In chemical terms, there is frequently a centre atom in addition to the four atoms at the vertices when these two forms are used as descriptors of molecular geometries. The central atom is inside the solid volume of the tetrahedron and equidistant from all four vertex atoms in the symmetrically-proper regular-tetrahedral geometry.

The electron pair geometry is tetrahedral, while the molecular geometry is a trigonal pyramid. The centre atom is trigonal pyramidal geometry can be inside the solid volume, confined inside a plane of the trigonal pyramid/tetrahedron, or even outside the tetrahedral volume. 

References 

  1. https://pubs.acs.org/doi/abs/10.1021/acs.accounts.8b00257
  2. https://pubs.rsc.org/en/content/articlelanding/2012/nr/c2nr31071f/unauth

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