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Differences between organic and inorganic compounds

By definition, organic chemistry is the study that includes all branches of carbon chemistry; therefore, it is logical to think that their skeletons are made up of carbon atoms. In contrast, inorganic skeletons (without entering polymers) are usually made up of any other element in the periodic table other than carbon.

Living things, in all their scales and expressions, are practically made of carbon and other heteroatoms (H, O, N, P, S, etc.). So all the greenery that covers the earth’s crust, as well as the creatures that walk on it, are living examples of complex and dynamically intermingled organic compounds.

On the other hand, drilling the earth and in the mountains we find mineral bodies rich in composition and geometric shapes, the vast majority of which are inorganic compounds . The latter also define almost entirely the atmosphere we breathe, and the oceans, rivers and lakes.

Organic compounds

Inorganic compounds

Atoms that compose it

They contain carbon atoms.

They are made up of elements other than carbon.

They are part of …

They are part of living beings.

They are part of inert beings.

Sources in which they are found

They are less abundant in natural sources.

They are more abundant in natural sources.

Types of compounds

They are usually molecular.

They are usually ionic.

Types of links

Covalent bonds.

Ionic bonds.

Molar masses

Larger molar masses.

Lower molar masses.

Diversity

They are less diverse.

They are more diverse elements.

Melting and boiling points

Lower melting and boiling points.

Higher melting and boiling points.

Main differences between organic and inorganic compounds

Inorganic compounds are obtained from more abundant natural sources than inorganic compounds

Crystals of sugar (right) and salt (left) seen under a microscope. Source: Oleg Panichev [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Although there may be exceptions, inorganic compounds are generally obtained from more abundant natural sources than those for organic compounds. This first difference leads to an indirect statement: inorganic compounds are more abundant (on Earth and in the Cosmos) than organic compounds.

Of course, in an oil field, hydrocarbons and the like, which are organic compounds, will predominate.

Returning to the section, the sugar-salt pair can be mentioned as an example. Shown above are the sugar crystals (more robust and faceted) and salt (smaller and rounded).

Sugar is obtained, after a series of processes, from sugar cane plantations (in sunny or tropical regions) and from sugar beets (in cold regions or at the beginning of winters or autumn). Both are natural and renewable raw materials, which are cultivated until their due harvest.

Meanwhile, salt comes from a much more abundant source: the sea, or lakes and deposits of salts such as the mineral halite (NaCl). If all the fields of sugarcane and sugar beets were brought together, they could never be equaled with the natural reserves of salt.

Inorganic crystals are usually ionic while organic crystals tend to be molecular

Taking again the sugar-salt pair as an example, we know that sugar consists of a disaccharide called sucrose, which in turn breaks down into a glucose unit and a fructose unit. Sugar crystals are therefore molecular, since they are defined by sucrose and its intermolecular hydrogen bonds.

The main point is that inorganic compounds usually form ionic crystals (or at least, possessing a high ionic character). However, there are several exceptions, such as crystals of CO 2 , H 2 S, SO 2 and other inorganic gases, which solidify at low temperatures and high pressures, and are also molecular.

Water represents the most important exception to this point: ice is an inorganic and molecular crystal.

The few snow or ice are water crystals, excellent examples of inorganic molecular crystals. Source: Sieverschar from Pixabay.

Minerals are essentially inorganic compounds, and their crystals are therefore predominantly ionic in nature. That is why this second point is considered valid for a wide spectrum of inorganic compounds, including salts, sulfides, oxides, tellides, etc.

The type of bond that governs organic compounds is covalent

The same sugar and salt crystals leave something in doubt: the former contain covalent (directional) bonds, while the latter exhibit ionic (non-directional) bonds.

This point is directly correlated with the second: a molecular crystal must necessarily have multiple covalent bonds (sharing of a pair of electrons between two atoms).

Again, organic salts establish certain exceptions, as they also have a strongly ionic character; for example, sodium benzoate (C 6 H 5 COONa) is an organic salt, but within the benzoate and its aromatic ring there are covalent bonds. Even so, its crystals are said to be ionic given the electrostatic interaction: C 6 H 5 COO  Na + .

In organic compounds, covalent bonds between carbon atoms predominate

Or what is the same to say: organic compounds consist of carbon skeletons. In them there is more than one CC or CH bond, and this backbone can be linear, ring, or branched, varying in the degree of its unsaturations and the type of substituent (heteroatoms or functional groups). In sugar, CC, CH and C-OH bonds are abundant.

Let’s take as an example the set CO, CH 2 OCH 2  and H 2 C 2 O 4 . Which of these three compounds are inorganic?

In CH 2 OCH 2 (ethylene dioxide) there are four CH bonds and two CO bonds, while in H 2 C 2 O 4 (oxalic acid) there are one CC, two C-OH, and two C = O. The structure of H 2 C 2 O 4 can be written as HOOC-COOH (two linked carboxyl groups). Meanwhile, CO consists of a molecule usually represented with a hybrid bond between C = O and C≡O.

Since in CO (carbon monoxide) there is only one carbon atom bonded to one of oxygen, this gas is inorganic; the other compounds are organic.

Organic compounds tend to have larger molar masses

Structure represented with lines for palmitic acid. It can be noted how large it is compared to smaller inorganic compounds, or to the formula weight of its salts. Source: Wolfgang Schaefer [Public domain]

Again, there are numerous exceptions to these rules, but in general organic compounds tend to have larger molar masses due to their carbon skeleton.

For example, the molars of the above compounds are: 28 g / mol (CO), 90 g / mol (H 2 C 2 O 4 ) and 60 g / mol (CH 2 OCH 2 ). Of course, CS 2 (carbon disulfide), an inorganic compound whose molar mass is 76 g / mol, “weighs” more than CH 2 OCH 2 .

But what about fats or fatty acids? From biomolecules like DNA or proteins? Or hydrocarbons with long linear chains? Or asphaltenes? Their molar masses easily exceed 100 g / mol. Palmitic acid (top image), for example, has a molar mass of about 256 g / mol.

Organic compounds are more abundant in number

Some inorganic compounds, called coordination complexes, do exhibit isomerism. However, it is less diverse compared to organic isomerism.

Even if we add all the salts, oxides (metallic and non-metallic), sulfides, tellurides, carbides, hydrides, nitrides, etc., we would not gather perhaps even half of the organic compounds that can exist in nature. Therefore, organic compounds are more abundant in number and richer in structures.

Inorganic compounds are elementally more diverse

However, according to elemental diversity, inorganic compounds are more diverse. Why? Because with the periodic table in hand you can build any type of inorganic compound; while an organic compound, it is limited only to the elements: C, H, O, P, S, N, and X (halogens).

We have many metals (alkali, alkaline earth, transition, lanthanides, actinides, those of the p block), and infinite options to combine them with various anions (usually inorganic); such as: CO 2- (carbonates), Cl  (chlorides), P 3- (phosphides), O 2- (oxides), OH  (hydroxides), SO 2- (sulfates), CN  (cyanides) , SCN  (thiocyanates), and many more.

Note that the CN  and SCN  anions appear to be organic, but are actually inorganic. Another confusion is marked by the oxalate anion, C 2 O 2- , which is organic and not inorganic.

Inorganic compounds have higher melting and boiling points

Again, there are several exceptions to this rule, as it all depends on which pair of compounds is being compared. However, sticking to inorganic and organic salts, the former tend to have higher melting and boiling points than the latter.

Here we find another implicit point: organic salts are susceptible to decomposition, as heat breaks their covalent bonds. Even so, we compared the pair calcium tartrate (CaC 4 H 4 O 6 ) and calcium carbonate (CaCO 3 ). CaC 4 H 4 O 6 decomposes at 600ºC, while CaCO 3 melts at 825ºC.

And that CaCO 3 is far from being one of the salts with the highest melting points, as in the cases of CaC 2 (2160 ºC) and CaS 2 (2525 ºC): calcium carbide and sulfide, respectively.

Organic compounds are rarer in the Universe

The simplest and most primitive organic compounds, such as methane, CH 4 , urea, CO (NH 2 ) 2 , or the amino acid glycine, NH 2 CH 2 COOH, are very rare species in the Cosmos compared to ammonia, carbon dioxide. carbon, titanium oxides, carbon, etc. In the Universe even the precursor materials of life are not frequently detected.

Organic compounds support life to a much greater degree than inorganic ones

The shell of a morrocoy consists of a mixture of bones covered by keratin, which are in turn composed of an inorganic matrix (hydroxyapatite and related minerals) and an organic matrix (collagen, cartilage and nerves). Source: Morrocoy_ (Geochelone_carbonaria) .jpg: The Photographerderivative work: The Photographer [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

The organic chemistry of carbon, applied to the understanding of metabolic processes, is transformed into biochemistry (and from the point of view of metal cations, into bioinorganic).

Organic compounds are the cornerstone of life (like the morrocoy in the image above), thanks to the CC bonds and the huge conglomerate of structures resulting from these bonds, and their interaction with inorganic salt crystals.

Returning to the sugar-salt pair, the natural sources of sugar are alive: they are crops that grow and die; But the same is not the case with the sources of salt: neither the seas nor the saline deposits are alive (in a physiological sense).

The plants and animals synthesize endless organic compounds, which integrate an extensive range of natural products (vitamins, enzymes, hormones, fats, dyes, etc.).

However, we cannot leave out the fact that water is the solvent of life (and it is inorganic); nor that oxygen is essential for cellular respiration (not to mention metallic cofactors, which are not inorganic compounds but cations). Therefore, the inorganic also plays a crucial role in defining life.

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