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Difference Between Tetrahedral and Trigonal Pyramid

Tetrahedral vs Trigonal Pyramid

If we are talking about geometry, a tetrahedron is a kind of pyramid that has four “equal” triangular sides or faces. Its base can be any of those faces and is often referred to as a triangular pyramid. It can also refer to a molecule which contains an atom with four pairs of electrons. These paisr of electrons bond with each other which gives it a perfect equal structure.

If the bonding pairs of those electrons are changed, then we will have a trigonal pyramid (one non-bonding and three bonding pairs). Simply put, a molecule that has one lone pair of atoms and three outer atoms are called a trigonal pyramid. This changes the pyramidal shape of the structure of the molecule because of the influence of the lone atom. Unlike the tetrahedral that have four “equal” sides, the trigonal pyramid has one atom as the apex and three identical atoms at the corners which makes a pyramidal base.

In molecular geometry, the bonding and non-bonding pairs of electrons and atoms affect the shape of a molecule. While the tetrahedral and trigonal pyramid both have pyramidal shape, their structures are different, and that is what sets these two apart.

In tetrahedral molecular geometry, a tetrahedral can only be achieved when all four substituent atoms are the same and all of them are placed at the corners of the tetrahedron. There are also cases when tetrahedral molecules are also considered as chiral. A chiral is used to describe an object that doesn’t have an internal plane of symmetry.

In molecular geometry, bonding and non-bonding atoms can greatly determine the shape of a molecule. Bonding atoms don’t have any general impact on the shape of a molecule while a lone or the non-bonding atom will greatly affect how the molecules will take its shape.

The shape of a trigonal pyramid is influenced by the lone atom in its apex. Since lone pairs push themselves away from the bonded pairs, they go further away from the three bonded atoms causing a bend in its structure and give the trigonal pyramid its unique shape.

The shape of the molecule also determines whether they are polar or non-polar as well. Tetrahedral molecules are non-polar because the similarities of the four atoms located at the corners of the pyramid will cancel each other out. Since all these atoms are similar to each other, the electric attraction between them is nullified.

A trigonal pyramid, on the other hand, have polar molecules because of the lone atom within its structure. This lone atom makes the electric attraction between the three atoms in the corner of the pyramidal structure possible.

Electronegativity values can only be obtained when opposite atoms attract each other. Even though symmetry is an important factor in determining a molecule’s polarity, there are also things that must be considered, such as bond polarity and molecular polarity. Bond polarity is determined through the bonds of the atoms in the molecule. Molecular polarity, on the other hand, is determined by the shape of the molecule.


1.A tetrahedral is a kind of pyramidal structure that has four “equal” triangular sides or faces (four identical atoms). A trigonal pyramid, on the other hand, has one lone atom and three identical atoms at its corners.
2.Tetrahedral molecules are non-polar while trigonal pyramids are polar.
3.The structure of a tetrahedral molecule will always be equal in length to each other while a trigonal pyramid’s structure will be influenced by the lone atom at its apex.

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  1. This isn’t technically correct—I came across this issue today and sorted it out even further. What you call a “tetrahedral” is more accurately described as a “regular tetrahedral” What is called a “tetrahedral” in my chemistry textbook has bond angles (at the central atom) of 109.5 degrees—not the 60 degrees needed to form a regular tetrahedral. So the textbook should more accurately call the shape a “trigonal pyramidal” or an “irregular tetrahedral”. Most often, an irregular tetrahedral aka trigonal pyramidal shape is what you’re going to see. The only way a perfectly regular tetrahedral will form is if we’re talking about 4 atoms of the same element self-binding without binding to anybody else…(e.g. maybe tetranitrogen?) in which case no atom would be a true center.

  2. this is correct

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