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There are two general classes of chemical compounds in nature. Some are derived from the different biochemical processes that give rise to life, and are called organic compounds. The others are chemical substances generated anywhere in the universe without the intervention of living beings, forming what we know as inorganic matter. In both cases, the compounds can be both ionic and covalent.
In this article, we will explore some examples of covalent compounds, classified according to their origin and according to their polarity.
What are covalent compounds?
A compound is a substance formed by the union of two or more chemical elements, such as water (H 2 O), which is made up of hydrogen and oxygen, or carbon dioxide (CO 2 ), which is made up of carbon and oxygen. .
Whether organic or inorganic, depending on the type of chemical bond by which the atoms are joined in a compound, this can be an ionic or covalent compound. Covalent compounds are those in which all the constituent atoms are linked together by covalent bonds, that is, bonds in which the valence electrons are shared between the linked atoms.
This type of bond occurs when the bonded atoms have similar electronegativities that do not differ from each other by more than 1.7 units (on the Pauling scale).
Types of Covalent Compounds
Covalent compounds can be of organic or inorganic origin. Furthermore, depending on whether the covalent bonds are polar or nonpolar, and depending on the molecular geometry, molecules can be both polar and nonpolar. This gives rise to a total of four classes of covalent chemical compounds which are:
- Nonpolar Organic Covalent Compounds
- Polar Organic Covalent Compounds
- Nonpolar Inorganic Covalent Compounds
- Polar Inorganic Covalent Compounds
What elements combine to form covalent compounds?
Covalent compounds are formed almost exclusively between elements that are very close on the periodic table, mainly between non-metallic elements (although there are some exceptions). An example of this are organic compounds, which are made up of carbon and one or several of the following elements: H, N, O, S, P and/or some halogen. The difference in electronegativities between these elements is always low enough to give rise to covalent bonds (either polar or nonpolar), so almost all organic compounds are covalent.
The same happens with many of the inorganic compounds formed by nonmetals. For example, acid oxides (formed between oxygen and another nonmetal) are covalent oxides that retain the OX covalent bond even when reacting with water or a metal.
Compounds formed by the union between metals are not considered covalent compounds, since in that case metallic, non-covalent bonds are formed. Finally, most compounds formed between metals and nonmetals are ionic (ionic oxides, binary or halide salts, and oxysalts, for example) rather than covalent. However, there are some exceptions, since acid oxides of transition metals such as chromium, manganese, tungsten (and others) are known to be covalent compounds.
Hereinafter, we will see 20 specific examples of each of these types of covalent compounds.
Examples of Nonpolar Organic Covalent Compounds
1.- Methane (CH 4 )
It is the simplest organic compound. This hydrocarbon is a completely nonpolar covalent compound due to the symmetry of the molecule in which all the small dipole moments of the CH covalent bonds cancel.
2.- Cyclopropane (C 3 H 6 )
Another example of a nonpolar hydrocarbon, in this case the simplest possible cyclic alkane.
3.- Benzene (C 6 H 6 )
Benzene is an aromatic hydrocarbon. It is a perfectly symmetrical and completely nonpolar planar molecule.
4.- Anthracene (C 10 H 8 )
Like benzene, anthracene is also a nonpolar covalent aromatic compound. It is the simplest polycyclic aromatic hydrocarbon of all.
5.- p-Benzoquinone (C 6 H 4 O 2 )
p-benzoquinone is a planar cyclic diketone in which the dipole moments of the two C=O bonds cancel each other out because they point in opposite directions. This makes it an example of a covalent compound, despite possessing polar bonds.
Examples of Polar Organic Covalent Compounds
6.- o-Benzoquinone (C 6 H 4 O 2 )
Unlike the example above, the ortho isomer of benzoquinone does not have the carbonyl (C=O) groups pointing in opposite directions, but instead both point in roughly the same direction. The dipole moments of these two bonds add together to give rise to a polar organic molecule.
7.- Ethanol (CH 3 CH 2 OH)
Ethanol is one of the most widely used alcohols in industry. It is the second simplest alcohol there is and is a polar organic covalent compound thanks to the polarity of the CO and OH bonds.
8.- Methylamine (CH 3 NH 2 )
This is the simplest member of the amines, a family of organic compounds derived from ammonia. The NH and CN bonds are polar. Furthermore, the fact that nitrogen has a trigonal pyramidal geometry makes the entire molecule polar.
9.- Acetone (CH 3 COCH 3 )
As in the benzoquinone example, acetone possesses a carbonyl group containing a polar C=O bond that is not counteracted by any other dipole moment, making the ketone a polar organic covalent compound.
10.- 1,1,1-trifluoroethane (CF 3 CH 3 )
Fluorine is the most electronegative element on the periodic table, making the CF bond a strongly polar covalent bond. Due to the tetrahedral arrangement of atoms around each carbon, the three fluorine atoms in 1,1,1-trifluoroethane produce a net dipole moment that makes this molecule a polar covalent compound.
Examples of Nonpolar Inorganic Covalent Compounds
11.- Carbon dioxide (CO 2 )
Despite being a product of cellular respiration, carbon dioxide is considered an inorganic compound. This gas has two identical polar covalent bonds pointing in opposite directions, so the molecule as a whole is nonpolar.
12.- Borane (BH 3 )
Borane is a planar compound with trigonal planar geometry in which the hydrogens point to the corners of an equilateral triangle. This cancels all the dipole moments of the three BH bonds, giving rise to a nonpolar covalent compound.
13.- Dinitrogen tetroxide (N 2 O 4 )
The NO bond is a slightly polar covalent bond, and the NN bond is a fully nonpolar covalent bond, making N 2 O 4 an example of a covalent compound. Additionally, as in other cases, the symmetry of the molecule cancels the dipole moments, turning it into a nonpolar compound. Like all nitrogen oxides, dinitrogen tetroxide is an inorganic compound.
14.- Sulfur hexafluoride (SF 6 )
This is another example of a covalent compound that has polar covalent bonds but, due to its great symmetry (octahedral, in this case), results in a nonpolar molecule.
15.- Carbon disulfide (CS 2 )
This is a compound very similar to carbon dioxide and shares the same characteristics, thus being another example of a nonpolar covalent inorganic compound.
Examples of Polar Inorganic Covalent Compounds
16.- Water (H 2 O)
Water is one of the most abundant chemical compounds on planet earth. It covers two thirds of the earth’s surface and is the basis of life. However, water is considered an inorganic compound. The OH bond is a strongly polar covalent bond, and the molecule has angular geometry, making water a polar molecule.
17.- Carbon monoxide (CO)
This poisonous gas that is produced as a by-product of the incomplete combustion of organic compounds has a polar covalent triple bond between carbon and oxygen. It is one of the simplest examples of polar inorganic covalent compounds.
18.- Hydrogen sulfide (H 2 S)
This is a compound with structural characteristics very similar to water by virtue of the fact that sulfur is part of the oxygen group in the periodic table. It is, therefore, a polar covalent compound.
19.- Nitrogen monoxide (NO)
For the same reasons that carbon monoxide is a polar covalent compound, nitrogen monoxide is too. It is also a dangerously reactive substance because it is a free radical.
20.- Ammonia (NH 3 )
Ammonia forms the basis of amines, but it is considered an inorganic compound. As in the methylamine example, the nitrogen in ammonia has a trigonal pyramidal geometry, so all dipole moments have a component pointing in the same direction, giving the molecule a net dipole moment.
References
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