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Chapter 3 The Second Step On The Path To Matter: Molecules What is it that makes the objects you see in your surroundings different from each other? What is it that discriminates their colours, shapes, smells, and tastes? Why is one substance soft, another hard, and yet another fluid? From what you have read so far, you may answer these questions saying, "The differences between their atoms do this". Yet, this answer is not sufficient, because if the atoms were the cause for these differences, then there would have to be billions of atoms bearing different properties from each other. In practice, this is not so. Many materials look different and bear different properties although they contain the same atoms. The reason for this is the different chemical bonds the atoms form among them to become molecules. On the way to matter, molecules are the second
step after atoms. Molecules are the smallest units determining the
chemical properties of matter. These small bodies are made up of
two or more atoms and some, of thousands of groups of atoms. Atoms
are held together inside molecules by chemical bonds determined
by the electromagnetic force of attraction, which means that these
bonds are formed on the basis of the electrical charges of the atoms.
The electrical charges of atoms, in turn, are determined by the
electrons on their outermost shell. The arrangement of molecules
in different combinations give rise to the diversity of matter we
see around us. The importance of the chemical bonds that lie at
the heart of the diversity of matter come forward at this very point.
ChemIcal Bonds This driving force, that is, the objective of the atoms to raise the number of electrons in their outermost shells to maximum, causes an atom to form three types of bonds with other atoms. These are the ionic bond, covalent bond and metallic bond. Commonly, special bonds categorised under the general title of "weak bonds" act between molecules. These bonds are weaker than the bonds formed by atoms to constitute molecules because molecules need more flexible structures to form matter. Let us now, in brief, see the properties of these bonds
and how they are formed. IonIc Bonds Covalent Bonds Let us give a simple example to explain covalent bonds
better. As we mentioned previously on the subject of electron shells,
atoms can carry a maximum of two electrons in their innermost electron
shells. The hydrogen atom has a single electron and it has the tendency
to increase the number of its electrons to two to become a stable
atom. Therefore, the hydrogen atom forms a covalent bond with a
second hydrogen atom. That is, the two hydrogen atoms share each
other's single electron as a second electron. Thus, the H2
molecule is formed. MetallIc Bonds Scientists are not able to answer the question as to
why electrons in the electron shells of the atoms have such a tendency.
Living organisms, most interestingly, owe their existence to this
tendency. The Next Step:Compounds In laboratories, new compounds are
produced everyday. Currently, it is possible to talk about almost
two million compounds. The simplest chemical compound can be as
small as the hydrogen molecule, while there are also compounds made
up of millions of atoms.1
The BuIldIng Block of LIfe: the
"Carbon" Atom Structures as diverse as the cell membrane, the horns of an elk, the trunk of a redwood, the lens of the eye, and the venom of a spider are composed of carbon compounds. Carbon, combined with hydrogen, oxygen, and nitrogen in many different quantities and geometric arrangements, results in a vast assortment of materials with vastly different properties. So, what is the reason for carbon's ability to form approximately 1.7 million compounds? One of the most significant properties
of carbon is its ability to form chains very easily by lining carbon
atoms up one after another. The shortest carbon chain is made up
of two carbon atoms. Despite the unavailability of an exact figure
on the number of carbons that make up the longest carbon chain,
we can talk about a chain with seventy links. If we consider that
the atom that can form the longest chain after the carbon atom is
the silicon atom forming six links, the exceptional position of
the carbon atom will be better understood.2
At this point, the form of the chain plays a very important role. In two carbon compounds, for example, if the carbon atoms are the same in number yet combined in different forms of chains, two different substances are formed. The abovementioned characteristics of the carbon atom produce molecules that are critical for life. Some carbon compounds' molecules consist of just a few atoms; others contain thousands or even millions. Also, no other element is as versatile as carbon in forming molecules with such durability and stability. To quote David Burnie in his book Life: Carbon is a very unusual element.
Without the presence of carbon and its unusual properties, it is
unlikely that there would be life on Earth.3 As the chemist Sidgwick stated above, the human mind
is insufficient to fully understand the potential of this atom that
has only six protons, six neutrons and six electrons. It is impossible
for even a single property of this atom, which is vital for life,
to form by chance. The carbon atom, like everything else, has been
created by Allah perfectly adapted for the bodies of living beings,
which Allah encompasses down to their very atoms. Intermolecular Bonds: Weak Bonds Well, how do molecules combine to form matter? Since molecules become stable after their formation, they no longer swap atoms. So, what holds them together? In an effort to answer this question, chemists produced different theories. Research showed that molecules are able to combine in different ways depending on the properties of the atoms in their composition. These bonds are very important for organic chemistry, which is the chemistry of living beings, because the most important molecules constituting life are formed due to their ability to form these bonds. Let us take the example of proteins. The complex three-dimensional shapes of proteins, which are the building blocks of living things, are formed thanks to these bonds. This means that the weak chemical bond between molecules is at least as necessary as the strong chemical bond between atoms for the formation of life. Certainly, the strength of these bonds must be of a certain measure. We can continue with the protein example. Molecules
called amino acids combine to form proteins, which are much larger
molecules. The atoms forming amino acids are combined by covalent
bonds. Weak bonds combine these amino acids in such a way as to
produce three-dimensional patterns. Proteins can function in living
organisms only if they have these three dimensional patterns. Therefore,
if these bonds did not exist, neither would the proteins, or, therefore,
life exist. How would the earth look if there were no water? Certainly, everywhere there would be desert. There would be abysses and horrific pits, in place of seas. The sky would seem cloudless and have a strange colour. In fact, it is extremely difficult for water, the basis of life on earth, to form. First, let us imagine that hydrogen and oxygen molecules, which are the components of water, are put in a glass bowl. Let us leave them in the bowl for a very long time. These gases may still not form water even if they remain in the bowl for hundreds of years. Even if they do, it would not be more than a very small amount at the very bottom of the bowl and that would happen in a very slow fashion, maybe over thousands of years. The reason why water forms so slowly under these circumstances is temperature. At room temperature, oxygen and hydrogen react very slowly.
Oxygen and hydrogen, when free, are found as H2
and O2 molecules. To combine to form the water molecule,
they must collide. As a result of this collision, the bonds forming
the hydrogen and oxygen molecules weaken, leaving no hindrance for
the combination of oxygen and hydrogen atoms. Temperature raises
the energy and therefore, the speed of these molecules, resulting
in an increase in the number of collisions. Thus, it accelerates
the course of the reaction. However, currently, no temperature high
enough to form water exists on earth. The heat required for the
formation of water was supplied during the formation of the earth,
which resulted in the emergence of so much water as to cover three
quarters of the earth's urface. At present, water evaporates and
rises to the atmosphere where it cools and returns to the earth
in the form of rain. That is, there is no increase in the quantity;
only a perpetual cycle. The MIraculous PropertIes of
Water Now, let us briefly see how water is formed chemically. The electrical charge of water is zero, that is, it is neutral. Yet, due to the sizes of the oxygen and hydrogen atoms, the oxygen component of the water molecule has a slightly negative charge and its hydrogen component has a slightly positive charge. When more than one water molecule come together, positive and negative charges attract each other to form a very special bond called "the hydrogen bond". The hydrogen bond is a very weak bond and it is incomprehensibly short-lived. The duration of a hydrogen bond is approximately one hundred billionth of a second. But as soon as a bond breaks, another one forms. Thus, water molecules adhere tightly to each other while also retaining their liquid form because they are combined with a weak bond. Hydrogen bonds also enable water to resist temperature
changes. Even if air temperature increases suddenly, water temperature
increases slowly and, similarly, if air temperature falls suddenly,
water temperature drops slowly. Large temperature changes are needed
to cause considerable changes in water temperature. The significantly
high thermal energy of water has major benefits for life. To give
a simple example, there is a great amount of water in our bodies.
If water adapted to the sudden vicissitudes of temperature in the
air at the same rate, we would suddenly develop fevers or freeze.
Let us answer this question with the example of a river:
When the weather is very cold, it is not the whole river, but only
the surface of it that freezes. Water reaches its heaviest state
at + 40° C, and as soon as it reaches this temperature, it immediately
sinks to the bottom. Ice is formed on top of water as a layer. Under
this layer, water continues to flow, and since + 40°C is a temperature
at which living organisms can survive, life in water continues.
1. L. Vlasov, D. Trifonov, 107 Stories About Chemistry, 1977, p. 117  2. L. Vlasov, D. Trifonov, 107 Stories About Chemistry, 1977, p. 118 3. David Burnie, Life, Eyewitness Science, London: Dorling Kindersley, 1996, p.8 4. Nevil V. Sidgwick, The Chemical Elements and Their Compounds, vol.1, Oxford: Oxford University Press, 1950, p.490 |
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