Is Tetrahedral Polar: Why, When and Detailed Facts


Is tetrahedral polar always or it can be nonpolar as well , all this facts and explanation are discussed in the article.

Tetrahedral is polar depending on geometry and can also be nonpolar. The three factors governing polarity are shape, electronegativity and dipole moment . All this concepts have been explained in detail in the sections followed .

What type of bond is a tetrahedral?

In a tetrahedral geometry/bond, the central atom will be attached with four groups/substituents. The four substituents may or may not be the same.

Consider the example of methane (CH4) where carbon is the central atom and the substituents attached to it are hydrogen (all four groups). So the methane molecule becomes symmetrical. Consider the molecule of H3PO4 (phosphoric acid), it is a tetrahedral molecule but it is an asymmetrical molecule.

is tetrahedral polar
is tetrahedral polar

Image credit : Wikipedia

So, a tetrahedral bond can have both symmetrical as well as asymmetrical geometry depending upon the type of substituents attached to it. The bond angle in the tetrahedral molecule is about 109.5 degrees. In symmetrical tetrahedral molecules e.g. (CH4) the bond angle can be calculated by the dot product of two vectors. The hybridization in tetrahedral molecule is sp3.

Why the angle of bond is 109.5 degrees in tetrahedral, let’s seek answer to this question. As we know valence shell electrons pair repulsion theory (or in short VSEPR theory) is very helpful in predicting the geometry of a molecule. So according to this theory, the atoms in the molecule will try to achieve the geometry which will minimize repulsion existing between the electrons in the valence shell of the atom (the atom under consideration).

So, in the case with tetrahedral molecule, the atoms will try to arrange in such a way that the repulsion between electrons in valence shell of atoms is minimized. And this causes the bond angle to be 109.5 degrees, meaning gives it that shape/geometry.

A tetrahedral molecule can be polar or nonpolar. It all depends on symmetry and electronegativity concept. A molecule that is symmetrical and the atoms attached to the central atom have almost same electronegativity, then the molecule will be nonpolar.

Whereas a molecule is unsymmetrical and the atoms attached to the central atom have difference in their electronegativity then this will lead to the formation of dipole, thus making the molecule polar.

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When is tetrahedral molecule polar?

A tetrahedral molecule will be polar when there are lone pairs present or we can also say when the molecule is asymmetrical and the electronegativity of the atoms surrounding the central atom are different. What will happen is, it will lead to the formation of dipole moment.

The reason that for a molecule to be polar there should be difference in electronegativity is, the atom which has greater electronegativity will try to pull the electron density towards itself. A negative charge is developed on side and a positive charge is developed on the other side. And why a dipole moment arises, making the molecule polar.

Let’s understand this concept by examining some tetrahedral molecules that are polar:

Fluoromethane (CH3F):

Its synonym is methyl fluoride. The central atom over here is the carbon atom to which three hydrogen atoms and one fluorine atom is attached. In appearance it is colorless (gas). Its odour I quite pleasant similar to ether (at high concentration). The observed density is 1.439g/L. The melting point is said to be -137.8 degrees Celsius and boils at -78.4 degrees Celsius. The observed solubility (in water) is 1.66L/kg. The gas is considered to be nontoxic.

Image credit : Quora

The polarity in fluoromethane is due to the difference electro negativities of the atoms. Among the atoms of CH3F fluorine has higher electronegativity, so it will gain partial negative charge and the other atoms will be seen to gain partial positive charge (there will be dipole moment which will not be zero).

Hence the molecule will be polar. (The electronegativity of carbon, hydrogen and fluorine is 2.55, 2.22, and 3.98 respectively). We can see that there exists a difference in the electronegativities of atoms which is a very important criteria for a molecule to be polar and thus CH3F molecule is polar.

Chloromethane (CH3Cl):

Its synonym is methyl Chloride. CH3Cl is an organic compound. In appearance it is a gas (colorless) with a sweet kind of odor. The observed density is about 1.003 g/ml (at a temperature of -23.8 degrees Celsius). The observed melting point is -97.4 degrees Celsius and boils at around -23.8 degrees Celsius. Its solubility in water is around 5.32 g/L-1.

Image credit : Wikipedia

The shape of the molecule is tetrahedral. The central atom is carbon and three hydrogen and one Chlorine atom is attached to it. The molecule of Chloromethane is seen to be asymmetrical. The hybridization in the molecule is observed to be sp3.

There is difference in the electronegativities of the atoms of CH3Cl which will lead to the formation of dipole moment (one end will have negative and the other end will have a positive charge). This makes the molecule to be polar.

Chloroform (CHCl3)

Also called as trichloromethane (an organic compound). In appearance it is a gas (colorless). The odor is somewhat pleasant kind. The observed density is 1.489 g/cm3 at a temperature of 25 degrees Celsius. The melting point is said to -63.5 degrees Celsius and boils at a temperature of 61.15 degrees Celsius. The solubility in water is observed to be 10.62 g/L at a temperature of zero degrees Celsius.

Image credit : Wikipedia

It is tetrahedral molecule (observed to have C3v symmetry). The central atom is carbon where one hydrogen and three Chlorine atoms are attached to it. The electronegativities of carbon, hydrogen and chlorine are unequal among which chlorine is more electronegative then the other atoms. So, the difference in electronegativities will give rise to dipole moment and thus making it to be polar.

Ammonia (NH3)

It is a very important compound in industrial field. In appearance it is a gas (colorless).The odor is pungent (quite strong). The density is seen to be 0.86 kg/m3. The melting point is observed to be -77.73 degrees Celsius and boils at around -33.34 degrees Celsius. NH3 is a tetrahedral molecule but its shape is trigonal pyramidal.

Image credit : Wikipedia

Here nitrogen is the central atom where three hydrogen atoms are attached. The molecule is seen to be asymmetrical. There is a difference in the electronegativity of the atoms which is an important criteria for a molecule to be polar. The electronegativities of nitrogen and hydrogen are 3.04 and 2.2 respectively. This electronegativity difference gives rise to dipole moment making the molecule polar.

How do you know if a structure is polar?

Structure helps us in determining the polarity of a molecule. Most of the times a symmetrical molecule is nonpolar and asymmetrical molecule is polar. As we know a dipole moment arises due to the unequal distribution of electrons between atoms.

Due to inequality in charges, they cannot cancel each other, thus making a molecule polar. So, important point to be noted, asymmetrical molecule with dipole moment having different electronegativities making a molecule to be polar.

Read more about : Triple Bond Examples: Detailed Insights And Facts

Does tetrahedral have a dipole moment?

For a tetrahedral to have a dipole moment, a molecule should be first polar. As we know tetrahedral molecule can be polar as well as nonpolar. For a tetrahedral or any molecule to be polar it should have difference in its electronegativities, only then a molecule can be polar.

The difference in electronegativity causes the atom with higher electronegativity to pull the electron density towards itself. One side of the molecule will acquire positive charge and the other will have negative charge. Thus giving rise to dipole moment. So a tetrahedral polar molecule with different electronegativities will give rise to dipole moment.

Tetrahedral Geometry is polar.

As discussed in the earlier sections a tetrahedral geometry which is symmetric will give rise to nonpolar molecule and the one with asymmetric geometry will give polar molecule as it will give rise to dipole moment. (The electronegativities of the molecule should be compulsorily different as if they are same, the charges can cancel each other and give rise to nonpolar molecules).

Is tetrahedral always polar?

No, it can be sometimes nonpolar as well as polar depending on factors like shape and electronegativity. If symmetric atoms have equal/same electronegativity it will lead to the formation of a polar molecule. Consider the molecule of methane (CH4).

The molecule has symmetrical geometry (it is tetrahedral). The electronegativity of carbon, hydrogen is 2.55, 2.22 respectively. The difference in electronegativity is not much. There will be no dipole moment or we can say dipole moment is zero.

Image credit : Wikipedia

Thus the molecule will be nonpolar. So, we can see that tetrahedral can be polar and nonpolar depending on factors like geometry and difference in electronegativity.

Sania Jakati

This is Sania Jakati from Goa. I am an aspiring chemist pursuing my post graduation in organic chemistry. I believe education is the key element that moulds you into a great human being both mentally and physically. I'm glad to be a member of scintillating branch of chemistry and will try my best to contribute whatever I can from my side and Lambdageeks is the best platform where I can share as well as gain knowledge at the same time. LinkedIn-https://www.linkedin.com/in/sania-jakati-0954101bb

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