- Main differences between organic and inorganic compounds
- Inorganic compounds are obtained from more abundant natural sources than inorganic compounds
- Inorganic crystals are usually ionic while organic crystals tend to be molecular
- The type of bond that governs organic compounds is covalent
- In organic compounds, covalent bonds between carbon atoms predominate
- Organic compounds tend to have larger molar masses
- Organic compounds are more abundant in number
- Inorganic compounds are elementally more diverse
- Inorganic compounds have higher melting and boiling points
- Organic compounds are rarer in the Universe
- Organic compounds support life to a much greater degree than inorganic ones
- References
The differences between organic and inorganic compounds are not always simple, nor do they obey an immutable rule, since when it comes to chemistry there are countless exceptions that contradict or question previous knowledge. However, there are characteristics that make it possible to discern among many compounds which ones are inorganic or not.
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. On the other hand, inorganic skeletons (without going into 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 lines 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.
Main differences between organic and inorganic compounds
| Organic compounds | Inorganic compounds |
|---|---|
| They contain carbon atoms | They are made up of elements other than carbon |
| They are part of living beings | They are part of inert beings |
| They are less abundant in natural sources | They are more abundant in natural sources |
| They are usually molecular | They are usually ionic |
| Covalent bonds | Ionic bonds |
| Larger molar masses | Lower molar masses |
| They are less diverse | They are more diverse elements |
| Lower melting and boiling points | Higher melting and boiling points |
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
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 sugar crystals (more robust and faceted) and salt (smaller and rounded).
Sugar is obtained, after a series of processes, from sugarcane 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 grown until their due harvest.
Meanwhile, salt comes from a much more abundant source: the sea, or lakes and salt deposits 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.
Meanwhile, salt crystals are made up of a network of Na + and Cl - ions, which define a face-centered cubic structure (fcc).
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 crystals of water, 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, since 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
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 the 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 up 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 3 2- (carbonates), Cl - (chlorides), P 3- (phosphides), O 2- (oxides), OH - (hydroxides), SO 4 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 4 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
The organic chemistry of carbon, applied in the understanding of metabolic processes, is transformed into biochemistry (and from the point of view of metal cations, into bioinorganics).
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 it is not the same with the sources of salt: neither the seas nor the saline deposits are alive (in a physiological sense).
Plants and animals synthesize a myriad of organic compounds, which make up 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); and neither that oxygen is essential for cellular respiration (not to mention the metallic cofactors, which are not inorganic compounds but cations). Therefore, the inorganic also plays a crucial role in defining life.
References
- Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
- Whitten, Davis, Peck & Stanley. (2008). Chemistry (8th ed.). CENGAGE Learning.
- Graham Solomons TW, Craig B. Fryhle. (2011). Organic Chemistry. Amines. (10th edition.). Wiley Plus.
- Helmenstine, Anne Marie, Ph.D. (July 03, 2019). The Difference Between Organic and Inorganic. Recovered from: thoughtco.com
- Texas Education Agency. (2019). Organic or Inorganic? Recovered from: texasgateway.org
- Sucrose. (sf). How Sugar is Made: an Introduction. Recovered from: sucrose.com
- Wikipedia. (2019). List of inorganic compounds. Recovered from: en.wikipedia.org