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# Tetrahedral Shape

## What is Tetrahedral Shape?

Last updated date: 22nd Mar 2023
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The tetrahedral shape is formed when four atoms in their elemental form covalently bond together. The word "tetra" means "four," and the word "hedral" represents a solid face. When we combine the definitions of these two terms, we learn that tetrahedral refers to a solid with four faces.

The study of different atoms that combine with one primary atom at the centre by bonding and forming a specific physical structure is known as molecular geometry. A three-dimensional molecule's molecular structure does not change rapidly and is found in nature in the same orientations. Tetrahedral geometry is common in molecules, and it has different bond angles. This article will explain what the tetrahedral shape of a molecule is and what compounds exist in the tetrahedral shape.

Tetrahedral Shape

## Tetrahedral Molecular Geometry

A central atom is located in the centre of a tetrahedral molecular geometry, with four substituents located at the corners of the tetrahedron. ${{109.5}^{o}{cos}^{-1}{}{(-⅓)}}$, are the bond angles. When all four substituents are the same and the tetrahedron is complete, it belongs to the point group ${{T}_{d}}$. Saturated carbon and silicon compounds exhibit this chemical geometry. Other molecules and ions with this geometry include the xenon tetroxide molecule ${{Xe}{O}_{4}}$, the perchlorate ion ${{Cl}{O}^{4-}}$, the sulphate ion ${{S}{O}_{4}^{2-}}$, the phosphate ion ${{P}{O}_{4}^{3-}}$, and tetrakis (triphenylphosphine) palladium.

## Possible Shapes of Tetrahedron

### 0 Lone Pairs

This molecule is composed of four evenly spaced ${{sp}^{3}}$ hybrid orbitals with bond angles of ${{109.5}^{o}}$. The orbitals have a tetrahedral pattern. Since each orbital has an atom at the end, the molecule has a tetrahedral structure.

### 1 Lone Pairs

These have trigonal pyramidal molecular geometries and are of the form ${{A}{X}_{3}{E}}$. A trigonal pyramidal structure is formed when three bonds and one lone pair occur on the central atom of the molecule. ${{sp}^{3}}$ hybridisation occurs at the centre atom in molecules with tetrahedral electron pair geometries. Ammonia $\left( NH_3 \right)$ is a pyramidal trigonal molecule.

### 2 Lone Pairs

These have the shape ${{A}{X}_{2}{E}_{2}}$ and curved angles, as seen in the case of water. This molecule is composed of four uniformly spaced ${{sp}^{3}}$ hybrid orbitals that produce bond angles of approximately ${{109.5}^{o}}$, which is close to ${{104.5}^{o}}$. The orbitals have a tetrahedral pattern. In two of the orbitals, lone electron pairs exist. The formula for compounds with this molecular shape will be ${{A}{X}_{4}}$.

## Tetrahedral Structure

The VSEPR theory heavily influences tetrahedral molecular geometry. VSEPR stands for valence-shell electron-pair repulsion; a theory that predicts molecule shape based on electron interactions in atoms' outer, or valence, shells. When the four substituent atoms are transition metals rather than the typical elements studied in organic chemistry (for example, hydrogen, oxygen, or nitrogen), the molecule takes on a square planar shape rather than the traditional tetrahedral molecular geometry. The central atom and four substituents are located on the same plane in the square planar shape, with the substituents representing each corner of the square.

## Examples of Tetrahedral Molecular Geometry

Tetrahedral molecular structures can be found in a wide range of molecules, the most common of which are methane ${{(}{C}{H}_{4}{)}}$, silane ${{(}{Si}{H}_{4}{)}}$, and thiazyl trifluoride ${{(}{NS}{F}_{3}{)}}$. Tetrahedral structures are shared by the phosphate ion ${{(}{P}{O}_{4}{)}^{3-}}$, the sulphate ion ${{(}{S}{O}_{4}{)}^{2-}}$, and the perchlorate ion ${{(}{Cl}{O}_{4}{)}^{-}}$.

## Important Questions

1. What is the symmetry of a tetrahedral molecule?

Ans. A regular tetrahedron has 12 rotational (or orientation-preserving) symmetries and a symmetry order of 24 when transformations that combine a reflection and a rotation are considered. Since there is exactly one such symmetry for each permutation of the vertices of the tetrahedron, the group of all (not necessarily orientation preserving) symmetries is isomorphic to the group ${{S}_{4}}$, the symmetric group of permutations of four objects. The set of orientation-preserving symmetries is known as the alternating subgroup ${{A}_{4}}$ of ${{S}_{4}}$.

2. Are tetrahedral and linear shaped molecules always nonpolar?

Ans. No. Polarity is caused by a difference in electronegativity between the ends/sides/points of a molecule. It may not be very polar in some cases, but it will be polar nonetheless. Consider the linear case, such as HCN or CO. Consider the tetrahedral case of ${{C}{H}_{3}{Cl}}$. Of course, there are many more examples in each category; in fact, there are far fewer cases of purely non-polar substances in each of these categories than polar substances.

## Key Features

• The tetrahedral shape is formed when four atoms in their elemental form covalently bond together.

• The word "tetrahedral" gives us a good idea of what this term means. The word "tetra" means "four," and the word "hedral" represents a solid face.

• A central atom is located in the centre of a tetrahedral molecular geometry, with four substituents located at the corners of the tetrahedron.

## Multiple Choice Questions

1. Which of the following molecules has tetrahedral geometry?

(a) ${{Si}{H}_{2}{Br}_{2}}$

(b) ${{Kr}{Cl}_{2}{F}_{2}}$

(c) ${{P}{Cl}_{5}}$

(d) ${{S}{F}_{4}}$

2. The atoms in a molecule of water adopt what kind of geometry?

(a) Trigonal Planar

(b) Linear shape

(c) Tetrahedral

(d) Octahedral

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## FAQs on Tetrahedral Shape

1. Why are tetrahedral complexes generally more intense in colour than octahedral complexes?

Tetrahedral complexes have a more intense colour than octahedral complexes due to the absorption of different wavelengths of light. The central atoms of the tetrahedral compound form bonds with four ligands. In contrast, octahedral complexes bind to 5 ligands via their central atom. Tetrahedral complexes absorb light at a lower wavelength than octahedral complexes. As a result, they have a brighter colour than octahedral compounds.

2. Why are different colours observed in octahedral and tetrahedral complexes for the same metal and same ligands?

The extent of d-orbital splitting varies between the octahedral and tetrahedral fields. The splitting of energy in the octahedral and tetrahedral fields is closely related. In tetrahedral fields, the wavelength of light and the Crystal Field Splitting Energy are related. As a result, for the same metal and ligands, octahedral complexes absorb more light than tetrahedral complexes. As a result, various colours are observed.

3. What are tetrahedral voids in FCC?

Closest packing produces two types of voids. A tetrahedral void is formed when a triangular void in a closest-packed layer is surrounded by four spheres. A tetrahedral void has a CN of four.

The number of tetrahedral voids per sphere (anion)=(number of tetrahedral voids around a sphere (anion)/no. of tetrahedral voids (no. of spheres around a void).

As a result, in a tightly packed arrangement, the number of tetrahedral voids is double the number of spheres (anions).

For fcc => Z effective(rank)=(1/8)x8 + (1/2)x6=4

If Z effective =n, no. of tetrahedral voids =2n

Thus no. of tetrahedral voids in fcc=2x4=8